bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrodynamic model forecasts as a guide for process studies on plankton and larval fish
Authors: Pedersen Ole P. , Slagstad Dag , Tande Kurt S. 
Published: September 2003

AbstractThe interaction between hydrography, zooplankton and capelin larvae was studied during a 15‐day survey in May 2001 in the southern part of the Barents Sea within the strategic programme Capelin and Herring in the Barents Sea Coexistence or Exclusion (BASECOEX). The spawning ground of capelin is found on shallow grounds close to the coast and after hatching the fish larvae are being transported offshelf towards the central part of the Barents Sea. The objective of the field study was to provide estimates of mortality and growth during the duration of the survey. Estimating vital rates requires sampling upon the same population over time. Areas feasible for studying these processes for capelin larvae would have to fulfil several conditions, such as moderate advection, high population numbers of larvae together with appropriate sampling techniques. This paper describes how a model approach may be used as a guideline for planning and executing a survey which has to meet the above conditions. Initially, the biological field was nowcasted with an Individual Based Model (IBM) at the start of the survey. The hydrodynamic model used in conjunction with the IBM required realistic weather forcing. Because of collecting and processing of the data, they are always lagging 1–2 days behind the current date. In order to solve the problem of nowcasting and forecasting we applied real data as far as we could and continued with forecasted weather for the next 5 days. This map was then utilized at sea as part of the information needed to decide where to place the sampling grid, and in the design of the layout of the grid. The model approach further enabled us to estimate the retention of water masses and consequently the capelin larvae and zooplankton populations within the region of study. The retention analysis shows that the advection in the selected area is significant, and after 2 weeks only a small fraction of the initial population is present in the original grid.
Relative resistance of Pacific salmon to infectious salmon anaemia virus
Authors: Rolland J B , Winton J R 
Published: September 2003

AbstractInfectious salmon anaemia (ISA) is a major disease of Atlantic salmon, Salmo salar, caused by an orthomyxovirus (ISAV). Increases in global aquaculture and the international movement of fish made it important to determine if Pacific salmon are at risk. Steelhead trout, Oncorhynchus mykiss, and chum, O. keta, Chinook, O. tshawytscha, coho, O. kisutch, and Atlantic salmon were injected intraperitoneally with a high, medium, or low dose of a Norwegian strain of ISAV. In a second challenge, the same species, except chum salmon, were injected with a high dose of either a Canadian or the Norwegian strain. Average cumulative mortality of Atlantic salmon in trial 1 was 12% in the high dose group, 20% in the medium dose group and 16% in the low dose group. The average cumulative mortality of Atlantic salmon in trial 2 was 98%. No signs typical of ISA and no ISAV‐related mortality occurred among any of the groups of Oncorhynchus spp. in either experiment, although ISAV was reisolated from some fish sampled at intervals post‐challenge. The results indicate that while Oncorhynchus spp. are quite resistant to ISAV relative to Atlantic salmon, the potential for ISAV to adapt to Oncorhynchus spp. should not be ignored.
Melano‐macrophage centres and their role in fish pathology
Authors: Agius C , Roberts R J 
Published: September 2003

AbstractMelano‐macrophage centres, also known as macrophage aggregates, are distinctive groupings of pigment‐containing cells within the tissues of heterothermic vertebrates. In fish they are normally located in the stroma of the haemopoietic tissue of the spleen and the kidney, although in amphibians and reptiles, and some fish, they are also found in the liver. They may also develop in association with chronic inflammatory lesions elsewhere in the body and during ovarian atresia. In higher teleosts, they often exist as complex discrete centres, containing lymphocytes and macrophages, and may be primitive analogues of the germinal centres of lymph nodes. Melano‐macrophage centres usually contain a variety of pigments, including melanins, and these increase in range and volume in older fish or in the presence of cachectic disease. Melano‐macrophage centres act as focal depositories for resistant intracellular bacteria, from which chronic infections may develop. Iron capture and storage in haemolytic diseases appears to be a primary function, but antigen trapping and presentation to lymphocytes, sequestration of products of cellular degradation and potentially toxic tissue materials, such as melanins, free radicals and catabolic breakdown products are among other functions that have been ascribed. Recent work suggests that they are a site of primary melanogenesis rather than mere storage. Melano‐macrophage centres increase in size or frequency in conditions of environmental stress and have been suggested as reliable biomarkers for water quality in terms of both deoxygenation and iatragenic chemical pollution.
Extra small virus‐like particles (XSV) and nodavirus associated with whitish muscle disease in the giant freshwater prawn,Macrobrachium rosenbergii
Authors: Qian D , Shi Z , Zhang S , Cao Z , Liu W , Li L , Xie Y , Cambournac I , Bonami J‐R 
Published: September 2003

AbstractA disease ofMacrobrachium rosenbergii, the giant freshwater prawn, farmed in China was recently recorded in Zhejiang, Jiangsu, Shanghai, Guangxi and Guangdong provinces. The clinical sign of the disease, which develops in post‐larvae (PL), is a whitish appearance of the muscles, particularly noticeable in the abdomen. Mortalities may reach 100% in some hatcheries. Investigations by transmission electron microscopy after negative staining of diseased PL homogenates showed the presence of two types of viral particles: one, unenveloped, icosahedral in shape, 26–27 nm in diameter, the second, much smaller, about 14–16 nm in diameter, designated extra small virus particle (XSV). The large virus has a genome with two pieces of ssRNA (RNA‐1 and RNA‐2), of 3 and 1.2 kb, respectively. Hybridization tests confirmed that this large virus is closely related toM. rosenbergiinodavirus (MrNV) which was isolated from diseased prawns in a hatchery in the French West Indies. Its very small size and hypothesized biochemical and biological characteristics suggest XSV is a new type of crustacean virus. As XSV has always been found associated with the larger virus (nodavirus) and is located in muscle and connective cells of diseased animals, it could be an autonomous virus, a helper‐type virus or a satellite‐like virus.
Pathology and immunohistochemistry in three species of salmonids after experimental infection with Flavobacterium psychrophilum
Authors: Ekman E , Norrgren L 
Published: September 2003

AbstractRainbow trout, Oncorhynchus mykiss (Walbaum), sea trout, Salmo trutta L., and Atlantic salmon, Salmo salar L., were experimentally infected with Flavobacterium psychrophilum in order to evaluate any species differences in susceptibility to the bacterium. Furthermore, differences in pathological changes and distribution of the bacteria in internal organs were studied. The bacteria were injected intraperitoneally in two doses, high dose (Hd) 1 × 107 colony forming units (CFU) fish−1 and low dose (Ld) 1 × 106 CFU fish−1. The mortalities in the Ld groups varied between 0 and 7.5% and in the Hd groups between 55–70%. No significant differences in mortality between the species were recorded. Clinical signs and pathological findings were similar in the three species and in accordance with those of rainbow trout fry syndrome. Rainbow trout showed more pronounced lesions in the spleen compared with the other species. Necrosis of renal tubular epithelium and haematopoietic tissue was most prominent in rainbow trout and Atlantic salmon. Intracellular eosinophilic droplets in the kidney tubular epithelium were a prominent finding in rainbow trout and sea trout surviving the infection. The distribution of the bacteria in internal organs was similar in the three species, as studied with immunohistochemistry.
Feed deprivation of channel catfish, Ictalurus punctatus (Rafinesque), influences organosomatic indices, chemical composition and susceptibility to Flavobacterium columnare
Authors: Shoemaker C A , Klesius P H , Lim C , Yildirim M 
Published: September 2003

AbstractWithholding feed has been suggested as a strategy to manage infectious disease of channel catfish, Ictalurus punctatus (Rafinesque). In a previous study, we demonstrated that deprivation of feed for as little as 7 days reduced innate resistance of catfish to Flavobacterium columnare. This study was conducted to evaluate the effect of feeding regimens [no feeding (NF), fed once every other day to satiation (FEOD) and fed once daily to satiation (FD)] on organosomatic indices, physiological changes and susceptibility of channel catfish to F. columnare. Fish that were not fed for 2 and 4 weeks had a significant increase (P < 0.05) in gutted weight:wet weight ratio and decrease in other organosomatic indices [gut index (GI), mesenteric fat index (MFI) and hepatosomatic index (HSI)]. Haematology was not effected by feeding regimen except at week 4, when a significantly higher haemoglobin level was observed in the NF fish. Serum protein did not differ at week 2, but the level at week 4 of the NF fish (35.91 mg mL−1) was significantly lower than that of the FD fish (41.77 mg mL−1). Significantly lower (P < 0.05) blood glucose (39.5 and 40.3 mg dL−1) and liver glycogen (1.7 and 1.8 mg g−1) were seen in the NF fish at weeks 2 and 4, respectively, as compared with blood glucose and liver glycogen levels of FD fish (67.5 and 92.8 mg dL−1 and 46.5 and 52.6 mg g−1 at weeks 2 and 4, respectively) and FEOD (82.8 and 85.5 mg dL−1 and 45.1 and 51.4 mg g−1 at weeks 2 and 4, respectively). Mortality in the NF fish caused by F. columnare (78%) was significantly higher (P < 0.05) than mortality in the FD and FEOD treatments (0.0 and 1.7%, respectively). Blood glucose and liver glycogen showed the same trend of low values for NF fish following challenge (week 6). Blood glucose, liver glycogen, GI and HSI are sensitive indicators for channel catfish deprived of feed (NF) for 4 weeks. Blood glucose and liver glycogen levels around 40 mg dL−1 and 2 mg g−1, respectively, are indicative of starvation in juvenile channel catfish. Moreover, NF fish were susceptible to F. columnare infection. Thus, it is suggested that in the absence of natural food, juvenile channel catfish should be fed at least once every other day to apparent satiation to maintain normal physiological function and improve resistance to F. columnare.
A comparison of epidemiological patterns of salmon lice, Lepeophtheirus salmonis, infections on farmed Atlantic salmon, Salmo salar L., in Norway and Scotland
Authors: Heuch P A , Revie C W , Gettinby G 
Published: September 2003

AbstractThis paper examines two large national data sets collected over several years and contrasts the patterns of sea lice, Lepeophtheirus salmonis (Krøyer, 1837), infections, the use of treatments and the occurrence of chalimus peaks between Norwegian and Scottish farms. Infection levels in Scotland were significantly higher in general over the period under study. For the chalimus stage group in the first quarter of the year, Norwegian mean abundance stayed below 10 lice per m2 while Scottish means reached 45 lice per m2 of fish skin per m3 of water. Both countries had more chalimus in summer than at other times of year, but in the last 3 months of the year Scottish fish had, on average, two to four times as many chalimus as Norwegian fish. Peaks of chalimus abundance were more frequent in Scotland, particularly in winter, but the most prominent peaks occurred in summer in both countries. In Scotland a marked mid‐year build‐up of mobile pre‐adult and adult stages was seen, and both countries showed a tendency for mobile counts on the second year fish to increase towards the end of the year. Scottish fish carried, on average, three times as many mobile lice per m2 of skin as Norwegian fish in the last 3 months of the year. The difference in lice loads was reflected in the greater use of veterinary medicines on Scottish farms. The higher infection levels in Scotland may be due to shallower and more enclosed water bodies used for farming, smaller and shallower pens, differences in sea water temperatures or in access to appropriate medication. The results highlight the importance of ensuring that effective veterinary medicines are available in the UK for the control of infection.
Lethality of bypass polymerases in Escherichia coli cells with a defective clamp loader complex of DNA polymerase III
Authors: Viguera Enrique , Petranovic Mirjana , Zahradka Davor , Germain Karine , Ehrlich Dusko S. , Michel Bénédicte 
Published: September 2003

Summary Escherichia coli DNA polymerase III (Pol III) is one of the best studied replicative DNA polymerases. Here we report the properties of an E. coli mutant that lacks one of the subunits of the Pol III clamp loader complex, Psi (ψ), as a result of the complete inactivation of the holD gene. We show that, in this mutant, chronic induction of the SOS response in a RecFOR‐dependent way leads to lethality at high temperature. The SOS‐induced proteins that are lethal in the holD mutant are the specialized DNA polymerases Pol II and Pol IV, combined with the division inhibitor SfiA. Prevention of SOS induction or inactivation of Pol II, Pol IV and SfiA encoding genes allows growth of the holD mutant, although at a reduced rate compared to a wild‐type cell. In contrast, the SOS‐induced Pol V DNA polymerase does not participate to the lethality of the holD mutant. We conclude that: (i) Psi is essential for efficient replication of the E. coli chromosome; (ii) SOS‐induction of specialized DNA polymerases can be lethal in cells in which the replicative polymerase is defective, and (iii) specialized DNA polymerases differ in respect to their access to inactivated replication forks.
Biofilm formation at the air–liquid interface by the Pseudomonas fluorescens SBW25 wrinkly spreader requires an acetylated form of cellulose
Authors: Spiers Andrew J. , Bohannon John , Gehrig Stefanie M. , Rainey Paul B. 
Published: September 2003

SummaryThe wrinkly spreader (WS) genotype of Pseudomonas fluorescens SBW25 colonizes the air–liquid interface of spatially structured microcosms resulting in formation of a thick biofilm. Its ability to colonize this niche is largely due to overproduction of a cellulosic polymer, the product of the wss operon. Chemical analysis of the biofilm matrix shows that the cellulosic polymer is partially acetylated cellulose, which is consistent with predictions of gene function based on in silico analysis of wss. Both polar and non‐polar mutations in the sixth gene of the wss operon (wssF ) or adjacent downstream genes (wssGHIJ ) generated mutants that overproduce non‐acetylated cellulose, thus implicating WssFGHIJ in acetylation of cellulose. WssGHI are homologues of AlgFIJ from P. aeruginosa, which together are necessary and sufficient to acetylate alginate polymer. WssF belongs to a newly established Pfam family and is predicted to provide acyl groups to WssGHI. The role of WssJ is unclear, but its similarity to MinD‐like proteins suggests a role in polar localization of the acetylation complex. Fluorescent microscopy of Calcofluor‐stained biofilms revealed a matrix structure composed of networks of cellulose fibres, sheets and clumped material. Quantitative analyses of biofilm structure showed that acetylation of cellulose is important for effective colonization of the air–liquid interface: mutants identical to WS, but defective in enzymes required for acetylation produced biofilms with altered physical properties. In addition, mutants producing non‐acetylated cellulose were unable to spread rapidly across solid surfaces. Inclusion in these assays of a WS mutant with a defect in the GGDEF regulator (WspR) confirmed the requirement for this protein in expression of both acetylated cellulose polymer and bacterial attachment. These results suggest a model in which WspR regulation of cellulose expression and attachment plays a role in the co‐ordination of surface colonization.
The Pseudomonas aeruginosa quinolone signal molecule overcomes the cell density‐dependency of the quorum sensing hierarchy, regulates rhl‐dependent genes at the onset of stationary phase and can be produced in the absence of LasR
Authors: Diggle Stephen P. , Winzer Klaus , Chhabra Siri Ram , Worrall Kathryn E. , Cámara Miguel , Williams Paul 
Published: September 2003

SummaryIn Pseudomonas aeruginosa, diverse exoproduct virulence determinants are regulated via N‐acylhomoserine lactone‐dependent quorum sensing. Here we show that 2‐heptyl‐3‐hydroxy‐4(1H)‐quinolone (PQS) is also an integral component of the quorum sensing circuitry and is required for the production of rhl‐dependent exoproducts at the onset of stationary phase. Analysis of spent P. aeruginosa culture supernatants revealed that PQS is produced at the end of exponential phase in the parent strain and in the late stationary phase of a lasR mutant. Mutants defective in both PQS production (pqsR‐) and response (pqsE‐) produced substantially reduced levels of exoproducts but retained wild‐type N‐butanoyl homoserine lactone (C4‐HSL) levels. In the wild type, provision of exogenous PQS at the time of inoculation significantly increased PA‐IL lectin, pyocyanin and elastase production during early stationary phase and promoted biofilm formation. Exogenous PQS but not PQS derivatives lacking the 3‐hydroxy group overcame the cell density but not growth phase‐dependent production of exoproducts. PQS also overcame the transcriptional and post‐transcriptional repression of lecA (which codes for the PA‐IL lectin) mediated via the negative regulators MvaT and RsmA respectively. Increased expression of lecA in the presence of exogenous PQS can be explained partially by increases in RhlR, RpoS and C4‐HSL levels. A refined model for quorum sensing in P. aeruginosa is presented.
Cationic antimicrobial peptides activate a two‐component regulatory system, PmrA‐PmrB, that regulates resistance to polymyxin B and cationic antimicrobial peptides in Pseudomonas aeruginosa
Authors: McPhee Joseph B. , Lewenza Shawn , Hancock Robert E. W. 
Published: September 2003

SummaryThe two‐component regulatory system PhoP‐PhoQ of Pseudomonas aeruginosa regulates resistance to cationic antimicrobial peptides, polymyxin B and aminoglycosides in response to low Mg2+ conditions. We have identified a second two‐component regulatory system, PmrA‐PmrB, that regulates resistance to polymyxin B and cationic antimicrobial peptides. This system responds to limiting Mg2+, and is affected by a phoQ, but not a phoP mutation. Inactivation of the pmrB sensor kinase and pmrA response regulator greatly decreased the expression of the operon encoding pmrA‐pmrB while expression of the response regulator pmrA in trans resulted in increased activation suggesting that the pmrA‐pmrB operon is autoregulated. Interposon mutants in pmrB, pmrA, or in an intergenic region upstream of pmrA‐pmrB exhibited two to 16‐fold increased susceptibility to polymyxin B and cationic antimicrobial peptides. The pmrA‐pmrB operon was also found to be activated by a number of cationic peptides including polymyxins B and E, cattle indolicidin and synthetic variants as well as LL‐37, a component of human innate immunity, whereas peptides with the lowest minimum inhibitory concentrations tended to be the weakest inducers. Additionally, we showed that the putative LPS modification operon, PA3552‐PA3559, was also induced by cationic peptides, but its expression was only partially dependent on the PmrA‐PmrB system. The discovery that the PmrA‐PmrB two‐component system regulates resistance to cationic peptides and that both it and the putative LPS modification system are induced by cationic antimicrobial peptides has major implications for the development of these antibiotics as a therapy for P. aeruginosa infections.
IcsA, a polarly localized autotransporter with an atypical signal peptide, uses the Sec apparatus for secretion, although the Sec apparatus is circumferentially distributed
Authors: Brandon Lauren D. , Goehring Nathan , Janakiraman Anuradha , Yan Arthur W. , Wu Tong , Beckwith Jon , Goldberg Marcia B. 
Published: September 2003

SummaryAsymmetric localization of proteins is essential to many biological functions of bacteria. Shigella IcsA, an outer membrane protein, is localized to the old pole of the bacillus, where it mediates assembly of a polarized actin tail during infection of mammalian cells. Actin tail assembly provides the propulsive force for intracellular movement and intercellular dissemination. Localization of IcsA to the pole is independent of the amino‐terminal signal peptide (Charles, M., Perez, M., Kobil, J.H., and Goldberg, M.B., 2001, Proc Natl Acad Sci USA 98: 9871–9876) suggesting that IcsA targeting occurs in the bacterial cytoplasm and that its secretion across the cytoplasmic membrane occurs only at the pole. Here, we characterize the mechanism by which IcsA is secreted across the cytoplasmic membrane. We present evidence that IcsA requires the SecA ATPase and the SecYEG membrane channel (translocon) for secretion. Our data suggest that YidC is not required for IcsA secretion. Furthermore, we show that polar localization of IcsA is independent of SecA. Finally, we demonstrate that while IcsA requires the SecYEG translocon for secretion, components of this apparatus are uniformly distributed within the membrane. Based on these data, we propose a model for coordinate polar targeting and secretion of IcsA at the bacterial pole.
Regulation of Salmonella typhimurium virulence gene expression by cationic antimicrobial peptides
Authors: Bader Martin W. , Navarre William Wiley , Shiau Whitney , Nikaido Hiroshi , Frye Jonathan G. , McClelland Michael , Fang Ferric C. , Miller Samuel I. 
Published: September 2003

SummaryCationic antimicrobial peptides (CAMP) represent a conserved and highly effective component of innate immunity. During infection, the Gram‐negative pathogen Salmonella typhimurium induces different mechanisms of CAMP resistance that promote pathogenesis in animals. This study shows that exposure of S. typhimurium to sublethal concentrations of CAMP activates the PhoP/PhoQ and RpoS virulence regulons, while repressing the transcription of genes required for flagella synthesis and the invasion‐associated type III secretion system. We further demonstrate that growth of S. typhimurium in low doses of the α‐helical peptide C18G induces resistance to CAMP of different structural classes. Inducible resistance depends on the presence of PhoP, indicating that the PhoP/PhoQ system can sense sublethal concentrations of cationic antimicrobial peptides. Growth of S. typhimurium in the presence of CAMP also leads to RpoS‐dependent protection against hydrogen peroxide. Because bacterial resistance to oxidative stress and CAMP are induced during infection of animals, CAMP may be an important signal recognized by bacteria on colonization of animal tissues.