bluuebunny/crossref_metadata_2025 huggingface dataset:
Two hundred years of a diverse Daphnia community in Lake Naivasha (Kenya): effects of natural and human‐induced environmental changes
Authors: Mergeay Joachim , Verschuren Dirk , Kerckhoven Liesbeth Van , Meester Luc De
Published: July 2004

1. We used fossil diapausing eggs extracted from 210Pb‐dated sediment cores to reconstruct historical changes in the Daphnia community of Lake Naivasha, a climate‐sensitive lake in Kenya which over the past 200 years has experienced a series of well‐documented natural and anthropogenic environmental changes.

2. Contiguous sampling and analysis of four cores yielded ephippial capsules of eight Daphnia species. Only two of these had been recorded previously in live collections from Lake Naivasha, and one species is new to science. The four more common species (Daphnia barbata, D. laevis, D. magna, and D. pulex) show striking differences in abundance patterns and population dynamics through time. Four other species (D. lumholtzi, D. curvirostris, D. longispina s.l., and Daphnia sp. nov. type Limuru.) appear to have been present only occasionally. Nevertheless, between 1895 and 1915 seven species of Daphnia inhabited Lake Naivasha simultaneously.

3. Despite considerable natural environmental change associated with climate‐driven lake‐level fluctuations, the Daphnia community of Lake Naivasha has been severely affected by human activities over the past century, especially the introduction of exotic fishes and water‐quality changes because of agricultural soil erosion. The recent reappearance of large‐bodied Daphnia species (D. magna, D. barbata, D. lumholtzi, Daphnia sp. nov. type Limuru) after 20–110 years of absence can be explained by their release from fish predation, following a dramatic increase in turbidity caused by excess clastic sediment input from eroded catchment soils. The small‐bodied species D. laevis has fared less well recently, presumably because the benefit of lowered predation pressure is counteracted by more pronounced negative effects of increased turbidity on this species and loss of submerged macrophyte beds which formerly served as predation refuge.

4. Our results suggest that, despite considerable environmental instability and the absence of specialised zooplanktivores, top‐down control of fish on large zooplankton is important in Lake Naivasha. Predation pressure from fish has led to clear‐cut shifts in local Daphnia species composition, but failed to drive the larger taxa to extinction.
The influence of crevice size on the protection of epilithic algae from grazers
Authors: Bergey Elizabeth A. , Weaver Jennifer E.
Published: July 2004

1. This study investigated how the size of crevices might affect their effectiveness as refuges for diatom‐dominated algal assemblages from the grazing minnow Campostoma anomalum.

2. Crevice size was manipulated by making fired‐clay substrates, using moulds to produce eight substrates with pits from 1.17 to 22.0 mm diameter. Non‐pitted clay‐stones and limestone were also tested. Cages were used to control the access of Campostoma to arrays of the 10 different algal‐colonised substrates. The grazing treatments were: open and grazed, caged and ungrazed, and a grazed cage control. The experiment was replicated in eight large outdoor tanks. After 3 weeks, substrates were brushed and chlorophyll a concentrations of the removed algae and the algae remaining in pits were measured.

3. The experiment was field‐validated by exposing arrays of substrates to grazing Campostoma in five pools of a limestone stream.

4. The clay‐stone and limestone substrates accrued similar algal biomass and assemblages.

5. Smaller crevices provided more protection against grazing than larger crevices. Specifically, pits with openings smaller than 2 mm protected the enclosed algal assemblages in both the tank and field experiments. Larger pits provided less protection and pits over 7 mm in diameter were heavily grazed and may even be preferentially grazed by Campostoma.

6. None of the tested pit sizes were protective against larval chironomid grazers in the tank experiment, demonstrating that differences in the grazer size influence the effectiveness of crevice refuges.
Predictive modelling and spatial mapping of freshwater fish and decapod assemblages using GIS and neural networks
Authors: Joy Michael K. , Death Russell G.
Published: July 2004

1. We used stream fish and decapod spatial occurrence data extracted from a national database and recent surveys with geospatial landuse data, geomorphologic, climatic, and spatial data in a geographical information system (GIS) to model fish and decapod occurrence in the Wellington Region, New Zealand.

2. To predict the occurrence of each species at a site from a common set of predictor variables we used a multi‐response, artificial neural network (ANN), to produce a single model that predicted the entire fish and decapod assemblage in one procedure.

3. The predictions from the ANN using this landscape scale data proved very accurate based on evaluation metrics that are independent of species abundance or probability thresholds. The important variables contributing to the predictions included the latitudinal and elevational position of the site reach, catchment area, average air temperature, the vegetation type, landuse proportions of the catchment, and catchment geology.

4. Geospatial data available for the entire regional river network were then used to create a habitat‐suitability map for all 14 species over the regional river network using a GIS. This prediction map has many potential uses including: monitoring and predicting temporal changes in fish communities caused by human activities and shifts in climate, identifying areas in need of protection, biodiversity hotspots, and areas suitable for the reintroduction of endangered or rare species.
Phylogeography of Trochodendron aralioides (Trochodendraceae) in Taiwan and its adjacent areas
Authors: Huang Shing‐Fan , Hwang Shih‐Ying , Wang Jenn‐Che , Lin Tsan‐Piao
Published: July 2004

Aim  This paper described current phylogeographical patterns of chloroplastic DNA variation of Trochodendron aralioides, a temperate tree species, and inferred its possible refugium in Taiwan. This information was compared with the known phylogeographical pattern of subtropical tree species.

Location  A total of 24 populations were sampled including 20 from Taiwan, two each from the Ryukyus and Japan.

Methods  A haplotype network was constructed by computer program TCS, various parameters of genetic diversity were calculated and neutrality was tested by computer program DnaSP. To examine the similarity of genetic structure among populations, a maximum parsimony tree was reconstructed by computer program PAUP*. The results of isozyme of T. aralioides from a previous publication were incorporated into this study to infer the phylogeographical history.

Results  Nine haplotypes according to six substitutions, two indels and one inversion of the two cpDNA intergenic spacer fragments (petG‐trnP and petA‐psbJ) of T. aralioides were recognized. Genetic structure of the population of Japan is totally different from those of Taiwan and the Ryukyus. In Taiwan, the genetic structure was differentiated among populations revealed by Gst = 0.700 and Nst = 0.542, and the population genetics was clearly spatially structured. Two population groups were recognized. The first group was distributed islandwide and extended to the Ryukyus. The second group contained five of the seven known haplotypes, and was restricted to the area between latitude 24°46′ and 24°06′ N.

Conclusions  In Taiwan, north‐central area between latitude 24°46′ and 24°06′ N is potentially a refugium during the last glaciations. This finding is contradicted to subtropical species as Cyclobalanopsis glauca.
Austro‐boreal disjunctions: a remarkable biogeographical pattern illustrated by Nan Ao Island, Guangdong, China
Authors: Lazell James
Published: July 2004

Aim  To document disjunct, insular populations of animals separated from similar conspecifics distributed to the north, inland and upland, and compare this pattern with that historically described for northern Florida and the Florida Keys islands.

Location  Nan Ao Island is on the Tropic of Cancer 117° E in the South China Sea, eastern Guangdong Province, China. There are archipelagos of islets extending south‐east, and several coastal islets around Nan Ao.

Methods  Five field surveys were made in 1999–2001. Voucher specimens were tagged, catalogued, and deposited in major museum collections. The comparable Floridian disjunct pattern was researched and described in overview.

Results  Five species – a toad, two lizards and two snakes – collected on Nan Ao and three satellite islands were added to the two previously documented species – a lizard and a snake – that fit the austro‐boreal disjunct pattern. One lizard and one snake are minor range extensions of a hundred or few km. One snake's Nan Ao population is disjunct by about 450 km and one lizard's by about 550 km. The small, semi‐fossorial, short‐legged toad is the most notable, separated from the main area of its range by about 800 km. This is similar to the greatest distance between north Floridian and Keys disjunct populations.

Main conclusions  (1) Seven Nan Ao species of terrestrial vertebrates are isolated and disjunct from conspecifics found to the north, upland and inland; this compares to five species showing a similar north Florida to Florida Keys pattern. (2) The Nan Ao species have no conspecifics known from the intervening area whereas four of the five Floridian species have conspecific, but dissimilar, populations in the gap. (3) Nan Ao and its satellite islets were high points on a large coastal plain at glacial maximum. (4) Holocene sea level rise and concomitant global warming may have isolated the Nan Ao relicts that had continuous distributions at glacial maximum. (5) The intervening mainland conspecific populations may have been replaced by tropical species that moved north along the mainland but failed to colonize the islands. (6) If so, significant adaptation to a warmer climate must have occurred to enable survival of the Nan Ao relicts to the present.
Should we use proportional sampling for species–area studies?
Authors: Schoereder José H. , Galbiati Carla , Ribas Carla R. , Sobrinho Tathiana G. , Sperber Carlos F. , DeSouza Og , Lopes‐Andrade Cristiano
Published: July 2004

Aim  In this paper we aim to show that proportional sampling can detect species–area relationships (SARs) more effectively than uniform sampling. We tested the contribution of alpha and beta diversity in ant communities as explanations for the SAR.

Location  Tropical forest remnants in Viçosa, Minas Gerais, Brazil (20 °45′ S, 42 °50′ W).

Methods  We sampled 17 forest remnants with proportional sampling. To disentangle sampling effects from other mechanisms, species richness was fitted in a model with remnant size, number of samples (sampling effects) and an interaction term.

Results  A SAR was observed independent of the number of samples, discarding sampling effects. Alpha diversity was not influenced by remnant size, and beta diversity increased with remnant size; evidence to the fact that habitat diversity within remnants could be the dominant cause of the SAR. Such a relationship between beta diversity and remnant area may have also arisen due to the combined effects of territoriality and aggregation of ant species.

Main conclusions  The proposed model, together with proportional sampling, allowed the distinction between sampling effects and other mechanisms.
Relative effects of climate change, isolation and competition on body‐size evolution in the Japanese field mouse, Apodemus argenteus
Authors: Millien Virginie
Published: July 2004

Aim  This paper examines body size variation in both recent and Quaternary populations of the Japanese field mouse Apodemus argenteus in order to assess the relative effects on body size of climate change, isolation and competitive interactions with its congeneric A. speciosus. Both temporal (since the Last Glacial Maximum, LGM) and spatial (over the Japanese archipelago) scales are considered.

Location  The small field mouse is widespread in Japan, and the specimens examined were collected from 10 localities on islands of widely differing area (from 4 km2 to 230,510 km2) and at latitudes ranging from 30.3° N to 45.1° N.

Methods  The effects of geographical factors such as latitude and island area on the size variation of A. argenteus were investigated, using the lower incisor size. In addition, the size of some specimens from two Quaternary localities was compared with the size of the extant specimens. Evolutionary rates of size change since the LGM were calculated in darwins. Hutchinson size ratios were used to examine the pattern of variation of the size segregation between the two Japanese field mice, A. argenteus and A. speciosus, in relation to time and space.

Results  There was a negative relationship between size and latitude among living A. argenteus populations. In addition, there was no effect of island area on body size, especially at higher latitudes. At lower latitudes, A. argenteus were larger on smaller islands, although this trend was not statistically significant. Quaternary specimens of A. argenteus were smaller in size than their living representatives. The interspecific size ratio between the two Japanese Apodemus was larger on smaller islands and at higher latitudes, and there has been a decrease in the size ratio between the two Apodemus since the LGM. Lastly, in accordance with the theory of character displacement, the small A. argenteus was larger in allopatry than in sympatry, whereas the large A. speciosus was smaller in allopatry than in sympatry.

Main conclusions  These results indicate that A. argenteus does not conform to Bergmann's rule or to the island rule. The variation in size for the small Japanese field mouse at both spatial and temporal scales may be related to climate change, with an additional effect of competition with the large field mouse, especially on smaller islands. The size convergence between the two Japanese Apodemus observed over the last 21,000 years may be explained by the diminution of available food resources due to the reduction of land mass areas following the LGM. It may also be the result of an evolution towards an optimal body size; a hypothesis previously proposed to explain the evolution of body size in island mammals. Lastly, the evolutionary rates of body size calculated for A. argenteus since the LGM are typical of rates calculated for other Quaternary mainland mammals, thus suggesting that the evolution in this species was not particularly rapid, as is often thought for island mammals.
Shear bond strength of microwaveable acrylic resin for denture repair
Authors: Ng E. T. L. , Tan L. H. H. , Chew B. S. H. , Thean H. P. Y.
Published: July 2004

summary  Microwaveable acrylic denture resins are believed to provide an effective means of repairing fractured dentures. This in vitro investigation compared the bond strength of a microwaveable acrylic resin as a denture repair material to two established auto‐polymerized resins. Fifty‐one specimens were made using Lucitone 199 as a simulated denture base, and were then divided into three groups of 17 samples each. Each test group was bonded with the following acrylic resins: Acron Mc, Rapid Repair and Palapress. A shear bond strength test was carried out 24 h after the samples were bonded. Fracture analysis showed that bond failure was adhesive for all groups. Shear bond values showed a statistically significant difference at P < 0·05 level between Acron Mc and Rapid Repair; Palapress and Rapid Repair, and indicated that Acron Mc and Palapress were superior to Rapid Repair as a repair material. However, there was no statistical difference found between Acron Mc and Palapress. Microwaveable acrylic resins produce repaired junctions of adequate strength.
Translucency of glass‐fibre‐reinforced composite materials
Authors: Nakamura T. , Tanaka H. , Kawamura Y. , Wakabayashi K.
Published: July 2004

summary  The purpose of this study was to examine the translucency of glass‐fibre‐reinforced composite framework materials. Vectris and FibreKor, as well as an experimental material, were the glass‐fibre‐reinforced framework materials used. Targis, Sculpture and Estenia were the types of particulate filler composites veneered onto frameworks. Specimens were fabricated from each material, 0·5 and 1·0 mm thick. In addition, laminate specimens, 1·5 mm thick, were fabricated. The translucency of each specimen was evaluated by determining its contrast ratio. The laminate specimens were examined for colour differences. The experimental framework material was more translucent than the enamel composite when it was not coloured, and was nearly as translucent as the dentine composite when coloured. The commercial tooth‐coloured framework materials were nearly as translucent as the dentine composite. It was found that it was possible to reproduce the same colour as the veneering dentine composite, when the framework thickness was 0·5 mm, except in the case of FibreKor. Within the limitations of this study, tooth‐coloured, glass‐fibre‐reinforced framework materials are nearly as translucent as the veneering dentine composite, but these materials affect the colour of the prosthesis if the thickness of the framework material is increased beyond a certain point.
Effect of traditional and alternative intracoronal bleaching agents on microhardness of human dentine
Authors: Chng H. K. , Yap A. U. J. , Wattanapayungkul P. , Sim C. P. C.
Published: July 2004

summary  The purpose of this study was to compare the effect of traditional and alternative bleaching agents on microhardness of human dentine when used intracoronally. Thirty‐six premolars were divided into six groups and bleaching agents were sealed into the pulp chambers as follows: group 1 – distilled water (control), group 2–30% hydrogen peroxide solution, group 3 – sodium perborate mixed with distilled water, group 4 – sodium perborate mixed with 30% hydrogen peroxide solution, group 5–35% carbamide peroxide gel, group 6–35% hydrogen peroxide gel. Access cavities were sealed and the teeth were stored in distilled water at 37°C. After 7 days, each tooth was sectioned at the cemento‐enamel junction level and microhardness testing was carried out on dentine. The results showed that treatment with 35% hydrogen peroxide gel, 30% hydrogen peroxide solution and 35% carbamide peroxide gel reduced the microhardness of outer dentine to a small extent while treatment with sodium perborate mixed with water and sodium perborate mixed with 30% hydrogen peroxide solution did not significantly alter the microhardness of dentine.
Effectiveness of wet and dry mercury vapour suppressant systems in a faculty of dentistry clinic
Authors: Sutow E. J. , Hall G. C. , MacLean C. A.
Published: July 2004

summary  The objective of this study was to determine the effectiveness of a liquid and a dry commercial mercury vapour suppressant system. Measurements were made in a student dental clinic, using a mercury vapour detector for periods up to 76 weeks. The two products examined were MerconTMvap liquid in a stock jar and the MerconTMtainer dry jar system. Amalgam scrap jars were removed from the study when the mercury vapour concentration in the jars exceeded the arbitrary cut‐off criterion of 0·05 mg Hg m−3. Results showed that the mercury vapour concentration in the liquid system exceeded the cut‐off criterion in 44 weeks or less, whereas the dry system remained below the detection limit (0·01 mg Hg m−3) for the maximum measurement period of 76 weeks. It was concluded that the dry system is more effective and reliable than the liquid system. The reliability of the liquid system may be influenced by contact of amalgam scrap with the portion of the inner wall of the jar that is not covered by liquid. It is proposed that amalgam scrap contaminates the wall with mercury during its insertion.
Effectiveness of two‐liquid silane primers on bonding sintered feldspathic porcelain with a dual‐cured composite luting agent
Authors: Nogami T. , Tanoue N. , Atsuta M. , Matsumura H.
Published: July 2004

summary  The purpose of the current study was to evaluate the effect of two‐component ceramic primers on the bond strength of a composite material joined to a sintered porcelain material. Two sizes of porcelain discs (VMK 68; 10 and 8 mm in diameter by 2·5 mm thick) were ground (No. 1000 SiC), and surface‐conditioned using one of the following systems: (i) unprimed, (ii) Liquid A of the Porcelain Liner M material (PLM‐A), (iii) Liquid B of Porcelain Liner M (PLM‐B), (iv) Liquids A and B of Porcelain Liner M (PLM‐AB), (v) Liquid A of the Tokuso Ceramics Primer material (TCP‐A), (vi) Liquid B of Tokuso Ceramics Primer (TCP‐B) and (vii) Liquids A and B of Tokuso Ceramics Primer (TCP‐AB). All specimens were bonded with the Bistite II dual‐cured composite luting agent, and shear bond strengths were determined both after 24 h immersion in water and after subsequent thermocycling (4–60 °C, 1 min each, 20 000 cycles). Of the seven groups assessed, two groups (PLM‐AB and TCP‐AB) showed the greatest bond strength both before (30·7 MPa for PLM‐AB and 29·7 MPa for TCP‐AB) and after (19·7 MPa for PLM‐AB and 22·4 MPa for TCP‐AB) thermocycling (P < 0·05). No significant differences were found between the PLM‐AB and TCP‐AB groups regardless of the application of thermocycling (P > 0·05). It can be concluded that both of the acid‐catalysed two‐liquid ceramic primers showed superior bonding to the unhydrolysed single‐liquid silane agents (PLM‐B and TCP‐A) when the feldspathic porcelain was bonded with the Bistite II luting composite.
Bonding between resin luting cement and glass infiltrated alumina‐reinforced ceramics with silane coupling agent
Authors: Nakamura S. , Yoshida K. , Kamada K. , Atsuta M.
Published: July 2004

summary  The purpose of this study was to evaluate the shear bond strengths of three dual‐cured resin luting cements (Linkmax HV, Panavia Fluoro Cement, and RelyX ARC) to glass‐infiltrated alumina‐reinforced ceramic material and the effect of four silane coupling agents (Clearfil Porcelain Bond, GC Ceramic Primer, Porcelain LinerM, and Tokuso Ceramic Primer) on the bond strength. The two type‐shaped of In‐Ceram alumina ceramic glass‐infiltrated specimens were untreated or treated with one of the four ceramic primers and then cemented together with one of the three dual‐cured resin luting cements. Half of the specimens were stored in water at 37°C for 24 h and the other half thermocycled 20 000 times before shear bond strength testing. Surface treatment by all silane coupling agents improved the shear bond strength compared with non‐treatment. The specimens treated with Clearfil Porcelain Bond showed significantly greater shear bond strength than any of the other three silane coupling agents regardless of resin luting cements and thermocycling except for the use of Panavia Fluoro Cement at 20 000 thermocycles. When the alumina‐reinforced ceramic material was treated with any silane coupling agent except GC Ceramic Primer and cemented with Linkmax HV, no significant differences in bond strength were noted between after water storage and after 20 000 thermocycles. After 20 000 thermocycles, all specimens except for the combined use of Clearfil Porcelain Bond or GC Ceramic Primer and Linkmax HV and GC Ceramic Primer and Panavia Fluoro Cement showed adhesive failures at the ceramic–resin luting cement interface.
Effect of various surface treatment methods on the bond strength of the heat‐pressed ceramic samples
Authors: Saraçoğlu A. , Cura C. , Çötert H. S.
Published: July 2004

summary  This in vitro study was conducted to evaluate the interaction between the shear bond strength and the surface treatment method for a commercial dental ceramic. Ninety bonded ceramic units were manufactured for this study. Each unit was made by luting two cylinder‐shaped ceramic samples to each other with a resin‐composite luting agent. The units were then divided into nine groups, containing 10 units in each group. Samples from each group were treated with one of the following: etching with 4·9% hydrofluoric acid for 10, 20 and 40 s, 9·5% hydrofluoric acid for 10, 20 and 40 s, 40% orthophosphoric acid for 40 s, air abrasion with alumina in 50‐μm particles, and grinding with a high‐speed diamond bur. The treated samples were then silanated and luted with a resin‐composite luting agent. The luted units were then loaded to failure. Two samples from each group were neither silanated nor luted after the surface treatment procedure, and morphological changes obtained by various surface treatment regimens were investigated by scanning electron microscopy. A statistically significant difference was observed among the mean shear bond strengths of the groups prepared with different surface treatment techniques (P = 0·00). Hydrofluoric acid appeared to be the most suitable chemical medium to produce a reliable ceramic bond. Etching time and concentration of the acidic medium were also observed as important prognostic variates. Orthophosphoric acid treatment was observed to be the least effective surface treatment method on the heat‐pressed ceramic samples. Physical applications such as bur grinding and air blasting maintained stronger bonds than the orthophosphoric acid, while producing weaker bonds than surfaces treated with hydrofluoric acid in all concentrations and etching periods. The effect of the silane priming agent was not considered in this study.
The effect of GoldbonderTM on the adhesion between porcelain and pure titanium
Authors: Yamada K. , Onizuka T. , Sumii T. , Swain M. V.
Published: July 2004

summary  The present study examines the effect of a GoldbonderTM on the adhesion between titanium and porcelain as measured by the strain energy release rate (G) associated with the interfacial fracture of porcelain and titanium. The influence of surface treatment of titanium prior to GoldbonderTM application was also examined. The porcelain side of the specimens was notched to the interface with a thin diamond saw, and then a pre‐crack was made at the metal–porcelain interface by a special jig. The samples were subjected to a four‐point bending test resulting in stable crack extension from which G was calculated. Both the cracked cross‐section of interface and peeled fracture surface were examined with scanning electron microscope (SEM). The mean G values were 81·57 ± 10·34, 46·01 ± 14·83, and 15·98 ± 1·76 J m−2 for the sandblasted surface with the GoldbonderTM, polished surface with the GoldbonderTM, and sandblasted surface with the PastebonderTM, respectively. The G values revealed significant differences (P < 0·01) between GoldbonderTM and PastebonderTM, and between the sandblasted and polished surfaces with GoldbonderTM. The SEM photographs and elemental analysis showed that GoldbonderTM developed both chemical and mechanical bonding to titanium and porcelain.
Perceived stress, pain and work performance among non‐patient working personnel with clinical signs of temporomandibular or neck pain
Authors: Suvinen T. I. , Ahlberg J. , Rantala M. , Nissinen M. , Lindholm H. , Könönen M. , Savolainen A.
Published: July 2004

summary  The aim of the present study was to assess the associations between different types of perceived stress, pain and work performance among non‐patients with clinical signs of muscle pain in the head/neck region. One‐fifth (n=241) of the 1339 media employees who had participated in a previous survey (Ahlberg J. et al., J Psychosom Res 2002; 53: 1077–1081) were randomly selected for standardized clinical examinations. Altogether 49% (n=118) of these subjects had clinical signs of temporomandibular and/or neck muscle pain and were enrolled in the present study. The mean age of the study sample was 46·9 years (s.d. 6·6) and the female to male distribution 2:1. Of the 118 employees 46·5% reported that the pain problem interfered with their ability to work. Perceived ability to work was not significantly associated with age, gender or work positions. According to logistic regression, reduced work performance was significantly positively associated with continuous pain [odds ratio (OR) 4·38; 95% CI 1·21–15·7], level of perceived pain severity (OR 1·30; 95% CI 1·04–1·63), and health stress (OR 2·08; 95% CI 1·22–3·54). The results of this study indicated an association between specific self‐reported stress regarding health and work issues, pain and work performance. From a preventive perspective this indicates a need for increased awareness about these associations on not only individual level but also at the organizational level and in health care.
Association of dietary habits with symptoms of temporomandibular disorders in Bangladeshi adolescents
Authors: Akhter R. , Hassan N. M. M. , Nameki H. , Nakamura K. , Honda O. , Morita M.
Published: July 2004

summary  The prevalences of signs and symptoms of temporomandibular disorder (TMD) in Bangladeshi adolescents and their associations with intake of various hard food items were investigated. A group of 1200 randomly selected high school students aged 12–17 years from three communities (rural, semi‐urban and urban) completed a questionnaire on dietary habits and presence of TMD symptoms and were examined clinically. In bivariate analysis, no significant relationship was observed between TMD symptoms and eating of hard foods. However, in logistic regression analysis, clicking showed a significant correlation with consumption of hard vegetable and fruits more than three times per week (P < 0·05). A statistically significant correlation was also observed between consumption of all hard food items (at least one item in each of the four categories of hard food) more than 12 times per week and pain in the temporomandibular joint (TMJ) (P < 0·05). A positive association was found between pain in the TMJ and older age (15–17 years) (P < 0·001). The prevalence of pain in the TMJ was significantly higher in males (P < 0·01). Prevalences of clicking and pain in the TMJ were significantly higher in subjects living in a rural area than in subjects living in an urban area (P < 0·01 and P < 0·01, respectively). Subjects having one or more decayed, missing and filled teeth (DMFT) showed significantly higher prevalences of clicking (P < 0·01) and restricted mouth opening (P < 0·01). The results suggest that prevalence of TMD symptoms are related to prolonged consumption of hard food items.
Impact of posterior occlusal support on the condylar position
Authors: Seedorf H. , Seetzen F. , Scholz A. , Sadat‐Khonsari M. R. , Kirsch I. , Jüde H. D.
Published: July 2004

summary  The purpose of this study was to investigate condylar displacement related to the loss of posterior occlusal support. Each of 23 subjects received one occlusal adjusted splint that covered all teeth from the right to the left second mandibular molar. None of the subjects had a third molar and none of them had a missing tooth or showed tooth mobility. The splint was inserted and vertical and horizontal condylar position was measured by an ultrasonic motion analyser. The splint was then unilateraly shortened tooth‐by‐tooth up to the canine tooth and the measurement was repeated after each shortening. Cutting off the splint's second molar on one side lead to a slight ipsilateral cranial motion of the condyle if subjects clenched with maximum voluntary force. If the second and first molar were cut off, a noticeable cranial condylar movement of about 0·3 mm was observed even when teeth occluded with low force. These results suggest that loss of posterior occlusal support as it happens in routine oral rehabilitation leads to a noticeable cranial condyle movement during registration, even if the clenching force is low.
Investigating the role of secA2 in secretion and glycosylation of a fimbrial adhesin in Streptococcus parasanguis FW213
Authors: Chen Qiang , Wu Hui , Fives‐Taylor Paula M.
Published: July 2004

Adhesion of Streptococcus parasanguis FW213, a primary colonizer, to the tooth surface is mediated mainly by peritrichous long fimbriae. The fimbrial structural unit, Fap1, is indispensable for fimbriae biogenesis, adhesion to an in vitro tooth model and biofilm formation. Mature Fap1 is a glycoprotein with an apparent molecular mass of 200 kDa. Glycosylated Fap1 is not present in some mutants screened from a transposon mutant library. Localization of the transposition sites revealed a gene determined to be secA2, which is distinct from the canonical secA gene. In FW213, glycosylated Fap1 was present in all the subcellular fractions including the cytoplasm. In VT1574, a non‐polar mutant of secA2 generated by in frame deletion, Fap1 was not secreted. Glycosylated Fap1 was present in the membrane and cytoplasm of the mutant, although in greatly reduced amounts. Fap1 secretion and abundance were restored when VT1574 was complemented by a plasmid‐borne secA2. The secretion defect of the secA2 mutation appears to be limited to a small group of proteins such as Fap1 and FimA. These data suggested that Fap1 secretion rather than glycosylation was the major effect of the deletion of secA2; however, this deletion also had an impact on Fap1 abundance. Two more secA2 mutants with different regions deleted were tested for their ability to secrete Fap1. One mutant was completely unable to secrete Fap1 while the other was able to secrete, but in a decreased amount. These data suggest that the region deleted in the latter mutant (nucleotides 2032–2337) is dispensable for Fap1 secretion.
Cyclic diguanylate (c‐di‐GMP) regulates Vibrio cholerae biofilm formation
Authors: Tischler Anna D. , Camilli Andrew
Published: July 2004

While studying virulence gene regulation in Vibrio cholerae during infection of the host small intestine, we identified VieA as a two‐component response regulator that contributes to activating expression of cholera toxin. Here we report that VieA represses transcription of Vibrio exopolysaccharide synthesis (vps) genes involved in biofilm formation by a mechanism independent of its phosphorelay and DNA‐binding activities. VieA controls the intracellular concentration of the cyclic nucleotide second messenger cyclic diguanylate (c‐di‐GMP) using an EAL domain that functions as a c‐di‐GMP phosphodiesterase. Two‐dimensional thin layer chromatography of nucleotide extracts confirmed that VieA reduces the concentration of c‐di‐GMP, opposing the action of  c‐di‐GMP synthetase proteins. Expression of unrelated V. cholerae c‐di‐GMP synthetase or phosphodiesterae proteins also modulated c‐di‐GMP concentration and vps gene expression. We propose that c‐di‐GMP synthetase and phosphodiesterase domain‐containing proteins contribute to regulating biofilm formation by controlling c‐di‐GMP concentration.
Light matters: phototaxis and signal transduction in unicellular cyanobacteria
Authors: Bhaya Devaki
Published: July 2004

Many photosynthetic microorganisms have evolved the ability to sense light quality and/or quantity and can steer themselves into optimal conditions within the environment. Phototaxis and gliding motility in unicellular cyanobacteria require type IV pili, which are multifunctional cell surface appendages. Screens for cells exhibiting aberrant motility uncovered several non‐motile mutants as well as some that had lost positive phototaxis (consequently, they were negatively phototactic). Several negatively phototactic mutants mapped to the tax1 locus, which contains five chemotaxis‐like genes. This locus includes a gene that encodes a putative photoreceptor (TaxD1) for positive phototaxis. A second chemotaxis‐like cluster (tax3 locus) appears to be involved in pilus biogenesis. The biosynthesis and regulation of type IV pilus‐based motility as well as the communication between the pilus motor and photosensory molecules appear to be complex and tightly regulated. Furthermore, the discovery that cyclic AMP and novel gene products are necessary for phototaxis/motility suggests that there might be additional levels of communication and signal processing.
Identification of activating region (AR) of Escherichia coli LysR‐type transcription factor CysB and CysB contact site on RNA polymerase alpha subunit at the cysP promoter
Authors: Lochowska Anna , Iwanicka‐Nowicka Roksana , Zaim Jolanta , Witkowska‐Zimny Malgorzata , Bolewska Krystyna , Hryniewicz Monika M.
Published: July 2004

CysB is a LysR‐type transcriptional regulator (LTTR) controlling the expression of numerous genes involved in bacterial sulphur assimilation via cysteine biosynthesis. Our previous mutational analysis of CysB identified several residues within the N‐terminal domain crucial for DNA‐binding function. Here, we focus on the functional significance of CysB residues localized in the turn between the α2 and α3 helices forming an N‐terminal helix–turn–helix motif. On the basis of the characteristics of alanine‐substituted mutants, we propose that CysB residues Y27, T28 and S29, lying in this turn region, comprise an ‘activating region’ (AR) that is crucial for positive control of the cysP promoter, but not for DNA binding and inducer response activities of CysB. Using a library of alanine substitutions in the C‐terminal domain of the RNAP α subunit (α‐CTD), we identify several residues in α‐CTD that are important for CysB‐dependent transcription from the cysP promoter. After probing potential protein–protein contacts in vivo with a LexA‐based two‐hybrid system, we propose that the ‘273 determinant’ on α‐CTD, including residues K271 and E273, represents a target for interaction with CysB at the cysP promoter.
Molecular analysis of the psa permease complex of Streptococcus pneumoniae
Authors: McAllister Lauren J. , Tseng Hsing‐Ju , Ogunniyi A. David , Jennings Michael P. , McEwan Alastair G. , Paton James C.
Published: July 2004

The psaBCA locus of Streptococcus pneumoniae encodes a putative ABC Mn2+‐permease complex. Downstream of the operon is psaD, which may be co‐transcribed and encodes a thiol peroxidase. Previously, there has been discordance concerning the phenotypic impact of mutations in the psa locus, resolution of which has been complicated by differences in mutant construction and the possibility of polar effects. Here, we constructed unmarked, in frame deletion mutants ΔpsaB, ΔpsaC, ΔpsaA, ΔpsaD, ΔpsaBC, ΔpsaBCA and ΔpsaBCAD in S. pneumoniae D39 to examine the role of each gene within the locus in Mn2+ uptake, susceptibility to oxidative stress, virulence, nasopharyngeal colonization and chain morphology. The requirement for Mn2+ for growth and transformation was also investigated for all mutants. Inductively coupled plasma mass spectrometry (ICP‐MS) analysis provided the first direct evidence that PsaBCA is indeed a Mn2+ transporter. However, this study did not substantiate previous reports that the locus plays a role in choline‐binding protein pro‐duction or chain morphology. We also confirmed the importance of the Psa permease in systemic virulence and resistance to superoxide and hydrogen peroxide, as well as demonstrating a role in nasopharyngeal colonization for the first time. Further evi‐dence is provided to support the requirement for Mn2+ supplementation for growth and transformation of ΔpsaB, ΔpsaC, ΔpsaA, ΔpsaBC, ΔpsaBCA and ΔpsaBCAD mutants. However, transformation, as well as growth, of the ΔpsaD mutant was not dependent upon Mn2+ supplementation. We also show that, apart from sensitivity to hydrogen peroxide, the ΔpsaD mutant exhibited essentially similar phenotypes to those of the wild type. Western blot analysis with a PsaD antiserum showed that deleting any of the genes upstream of psaD did not affect its expression. However, we found that deleting psaB resulted in decreased expression of PsaA relative to that in D39, whereas deleting both psaB and psaC resulted in at least wild‐type levels of PsaA.
Analysis in vitro and in vivo of the transcriptional regulator CrgA of Neisseria meningitidis upon contact with target cells
Authors: Deghmane Ala‐Eddine , Giorgini Dario , Maigre Laure , Taha Muhamed‐Kheir
Published: July 2004

Contact between CrgA, a LysR‐like regulatory protein in Neisseria meningitidis, and DNA is involved in the repression of several bacterial genes upon contact with epithelial cells. We used a defined in vitro system containing crgA promoter, purified RNA polymerase (RNAP) and purified CrgA protein to demonstrate that CrgA was directly responsible for this transcriptional repression. Interaction between the C‐terminal domain of CrgA and the RNAP led to the production of short abortive transcripts, suggesting that CrgA may act by preventing RNAP from clearing the promoter. We probed the regulation by CrgA of its own production by analysing CrgA–DNA contacts during cell–bacteria interaction by assaying in vivo protection against dimethyl sulphate (DMS) methylation. Comparison of DMS footprints in vitro and in vivo suggested that CrgA repressed transcription through specific base contacts, probably in the major groove of the DNA double helix, resulting in DNA looping. Upon contact with target cells, CrgA was released from the DNA, allowing transcription of the target gene to proceed to elongation and facilitating tight control of the expression of genes regulated by CrgA.
Neisseria meningitidis accelerates ferritin degradation in host epithelial cells to yield an essential iron source
Authors: Larson Jason A. , Howie Heather L. , So Magdalene
Published: July 2004

In order to colonize humans and cause disease, pathogenic bacteria must assimilate iron from their host. The vast majority of non‐haem iron in humans is localized intracellularly, within the storage molecule ferritin. Despite the vast reserves of iron within ferritin, no pathogen has been demonstrated previously to exploit this molecule as an iron source. Here, we show that the Gram‐negative diplococcus Neisseria meningitidis can trigger rapid redistribution and degradation of cytosolic ferritin within infected epithelial cells. Indirect immunofluorescence microscopy revealed that cytosolic ferritin is aggregated and recruited to intracellular meningococci (MC). The half‐life of ferritin within cultured epithelial cells was found to decrease from 20.1 to 5.3 h upon infection with MC. Supplementation of infected epithelial cells with ascorbic acid abolished ferritin redistribution and degradation and prevented intracellular MC from replicating. The lysosomal protease inhibitor leupeptin slowed ferritin turnover and also retarded MC replication. Our laboratory has shown recently that MC can interfere with transferrin uptake by infected cells (Bonnah R.A., et al., 2000, Cell Microbiol 2: 207–218) and that, perhaps as a result, the infected cells have a transcriptional profile indicative of iron starvation (Bonnah, R.A., et al., 2004, Cell Microbiol 6: 473–484). In view of these findings, we suggest that accelerated ferritin degradation occurs as a response to an iron starvation state induced by MC infection and that ferritin degradation provides intracellular MC with a critical source of iron.
Translation repression by an RNA polymerase elongation complex
Authors: Wilson Helen R. , Zhou Jian‐guang , Yu Daiguan , Court Donald L.
Published: July 2004

Bacteriophage λ N and bacterial Nus proteins together with a unique site NUT in the leader of the early viral N gene transcript bind RNA polymerase (RNAP) and form a highly processive antitermination complex; N bound at NUT also represses N translation. In this study, we investigate whether N and NUT cause N translation repression as part of the antitermination complex by testing conditions that inhibit the formation of the N‐modified transcription complex for their effect on N‐mediated translation repression. We show that nus and nut mutations that in combination destabilize multiple interactions in the antitermination complex prevent N‐mediated translation repression. Likewise, transcription of the nut‐N region by T7 RNAP, which does not lead to the assembly of an effective antitermination complex when N is supplied, eliminates translation repression. We also demonstrate that a unique mutant β subunit of RNAP reduces N‐mediated translation repression, and that overexpression of transcription factor NusA suppresses this defect. We conclude that the N‐modified RNAP transcription complex is necessary to repress N translation.
The bromodomain‐containing protein Bdf1p acts as a phenotypic and transcriptional multicopy suppressor of YAF9 deletion in yeast
Authors: Bianchi Michele M. , Costanzo Giovanna , Chelstowska Anna , Grabowska Dorota , Mazzoni Cristina , Piccinni Eugenia , Cavalli Antonella , Ciceroni Francesca , Rytka Joanna , Slonimski Piotr P. , Frontali Laura , Negri Rodolfo
Published: July 2004

It was observed previously that the deletion of the open reading frame YNL107w (YAF9) was highly pleiotropic in yeast and caused defective growth phenotypes in the presence of several unrelated inhibitors, including caesium chloride. We have selected multicopy extragenic suppressor genes, revealing that this phenotype can be suppressed by overdosing the transcription factors BDF1 and GAT1 in the yaf9Δ strain. We focused our analysis on suppression by BDF1 and performed a genome‐wide transcript analysis on a yaf9Δ strain, compared with the wild‐type and BDF1‐suppressed strains. YAF9 deletion has a clear effect on transcription and leads to modulation of the level of expression of several genes. Transcription of a considerable portion of the underexpressed genes is restored to wild‐type levels in the BDF1‐suppressed strain. We show by chromatin immunoprecipitation that both Yaf9p and Bdf1p bind to promoters of some of these genes and that the level of H3 and H4 acetylation at one of these promoters is significantly lowered in the yaf9 deleted strain, compared with the wild‐type and the BDF1‐suppressed strains.
Glycosomes: parasites and the divergence of peroxisomal purpose
Authors: Parsons Marilyn
Published: July 2004

Peroxisomes are membrane‐bounded organelles that compartmentalize a variety of metabolic functions. Perhaps the most divergent peroxisomes known are the glycosomes of trypanosomes and their relatives. The glycolytic pathway of these organisms resides within the glycosome. The development of robust molecular genetic and proteomic approaches coupled with the completion of the genome sequence of the pathogens Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major provides an opportunity to determine the complement of proteins within the glycosome and the function of compartmentation. Studies now suggest that regulation of glycolysis is a strong driving force for maintenance of the glycosome.
Chemical communication in proteobacteria: biochemical and structural studies of signal synthases and receptors required for intercellular signalling
Authors: Pappas Katherine M. , Weingart Christine L. , Winans Stephen C.
Published: July 2004

Cell–cell communication via the production and detection of chemical signal molecules has been the focus of a great deal of research over the past decade. One class of chemical signals widely used by proteobacteria consists of N‐acyl‐homoserine lactones, which are synthesized by proteins related to LuxI of Vibrio fischeri and are detected by proteins related to the V. fischeri LuxR protein. A related marine bacterium, Vibrio harveyi, communicates using two chemical signals, one of which, autoinducer‐2 (AI‐2), is a furanone borate diester that is synthesized by the LuxS protein and detected by a periplasmic protein called LuxP. Evidence from a number of laboratories suggests that AI‐2 may be used as a signal by diverse groups of bacteria, and might permit intergeneric signalling. These two families of signalling systems have been studied from the perspectives of physiology, ecology, biochemistry, and more recently, structural biology. Here, we review the biochemistry and structural biology of both acyl‐homoserine‐lactone‐dependent and AI‐2‐dependent signalling systems.