bluuebunny/crossref_metadata_2025_split huggingface dataset:
Freshwater Bacteria Can Methylate Selenium through the Thiopurine Methyltransferase Pathway
Authors: Ranjard Lionel , Nazaret Sylvie , Cournoyer Benoit 
Published: July 2003

ABSTRACT

Involvement of the bacterial thiopurine methyltransferase (bTPMT) in natural selenium methylation by freshwater was investigated. A freshwater environment that had no known selenium contamination but exhibited reproducible emission of dimethyl selenide (DMSe) or dimethyl diselenide (DMDSe) when it was supplemented with an organic form of selenium [(methyl)selenocysteine] or an inorganic form of selenium (sodium selenite) was used. The distribution of the bTPMT gene (
tpm
) in the microflora was studied. Freshwater bacteria growing on 10 μM sodium selenite and 10 μM sodium selenate were isolated, and 4.5 and 10% of the strains, respectively, were shown by colony blot hybridization to hybridize with a
Pseudomonas syringae tpm
DNA probe. Ribotyping showed that these strains are closely related. The complete
rrs
sequence of one of the strains, designated Hsa.28, was obtained and analyzed. Its closest phyletic neighbor was found to be the
Pseudomonas anguilliseptica rrs
sequence. The Hsa.28 strain grown with sodium selenite or (methyl)selenocysteine produced significant amounts of DMSe and DMDSe. The Hsa.28
tpm
gene was isolated by genomic DNA library screening and sequencing. BLASTP comparisons of the deduced Hsa.28 bTPMT sequence with
P. syringae
,
Pseudomonas aeruginosa
,
Vibrio cholerae
, rat, and human thiopurine methyltransferase sequences revealed that the levels of similarity were 52 to 71%. PCR-generated
Escherichia coli
subclones containing the Hsa.28
tpm
open reading frame were constructed.
E. coli
cells harboring the constructs and grown with sodium selenite or (methyl)selenocysteine produced significant levels of DMSe and DMDSe, confirming that the gene plays a role in selenium methylation. The effect of strain Hsa.28 population levels on freshwater DMSe and DMDSe emission was investigated. An increase in the size of the Hsa.28 population was found to enhance significantly the emission of methyl selenides by freshwater samples supplemented with sodium selenite or (methyl)selenocysteine. These data suggest that bTPMT can play a role in natural freshwater selenium methylation processes.
Determination of In Situ Bacterial Growth Rates in Aquifers and Aquifer Sediments
Authors: Mailloux Brian J. , Fuller Mark E. 
Published: July 2003

ABSTRACTLaboratory and field-scale studies with stained cells were performed to monitor cell growth in groundwater systems. During cell division, the fluorescence intensity of the protein stain 5-(and 6-)-carboxyfluorescein diacetate succinimidyl ester (CFDA/SE) for each cell is halved, and the intensity can be tracked with a flow cytometer. Two strains of bacteria,Comamonassp. strain DA001 andAcidovoraxsp. strain OY-107, both isolated from a shallow aquifer, were utilized in this study. The change in the average generation or the average fluorescence intensity of the CFDA/SE-stained cells could be used to obtain estimates of doubling times. In microcosm experiments, the CFDA/SE-based doubling times were similar to the values calculated by total cell counting and were independent of cell concentration. Intact and repacked sediment core experiments with the same bacteria indicated that changes in groundwater chemistry were just as important as growth rates in determining planktonic cell concentrations. The growth rates within the sediment cores were similar to those calculated in microcosm experiments, and preferential transport of the daughter cells was not observed. The experiments indicated that the growth rates could be determined in systems with cell losses due to other phenomena, such as attachment to sediment or predation. Application of this growth rate estimation method to data from a field-scale bacterial transport experiment indicated that the doubling time was approximately 15 days, which is the first known direct determination of an in situ growth rate for bacteria in an aquifer.
Susceptibility and Adaptive Response to Bile Salts in
Propionibacterium freudenreichii
: Physiological and Proteomic Analysis
Authors: Leverrier Pauline , Dimova Diliana , Pichereau Vianney , Auffray Yanick , Boyaval Patrick , Jan Gwénaël 
Published: July 2003

ABSTRACT

Tolerance to digestive stresses is one of the main factors limiting the use of microorganisms as live probiotic agents. Susceptibility to bile salts and tolerance acquisition in the probiotic strain
Propionibacterium freudenreichii
SI41 were characterized. We showed that pretreatment with a moderate concentration of bile salts (0.2 g/liter) greatly increased its survival during a subsequent lethal challenge (1.0 g/liter, 60 s). Bile salts challenge led to drastic morphological changes, consistent with intracellular material leakage, for nonadapted cells but not for preexposed ones. Moreover, the physiological state of the cells during lethal treatment played an important role in the response to bile salts, as stationary-phase bacteria appeared much less sensitive than exponentially growing cells. Either thermal or detergent pretreatment conferred significantly increased protection toward bile salts challenge. In contrast, some other heterologous pretreatments (hypothermic and hyperosmotic) had no effect on tolerance to bile salts, while acid pretreatment even might have sensitized the cells. Two-dimensional electrophoresis experiments revealed that at least 24 proteins were induced during bile salts adaptation. Identification of these polypeptides suggested that the bile salts stress response involves signal sensing and transduction, a general stress response (also triggered by thermal denaturation, oxidative toxicity, and DNA damage), and an alternative sigma factor. Taken together, our results provide new insights into the tolerance of
P. freudenreichii
to bile salts, which must be taken into consideration for the use of probiotic strains and the improvement of technological processes.
Influence of Surface Characteristics on the Stability of
Cryptosporidium parvum
Oocysts
Authors: Butkus Michael A. , Bays J. Timothy , Labare Michael P. 
Published: July 2003

ABSTRACT

Microelectrophoresis is a common technique for probing the surface chemistry of the
Cryptosporidium parvum
oocyst. Results of previous studies of the electrophoretic mobility of
C. parvum
oocysts in which microelectrophoresis was used are incongruent. In this work we demonstrated that capillary electrophoresis may also be used to probe the surface characteristics of
C. parvum
oocysts, and we related the surface chemistry of
C. parvum
oocysts to their stability in water. Capillary electrophoresis results indicated that oocysts which were washed in a phosphate buffer solution had neutrally charged surfaces. Inactivation of oocysts with formalin did not influence their electrophoretic mobility, while oocyst populations that were washed in distilled water consisted of cells with both neutral and negative surface charges. These results indicate that washing oocysts in low-ionic-strength distilled water can impart a negative charge to a fraction of the oocysts in the sample. Rapid coagulation experiments indicated that oocysts did not aggregate in a 0.5 M NaCl solution; oocyst stability in the salt solution may have been the result of Lewis acid-base forces, steric stabilization, or some other factor. The presence of sucrose and Percoll could not be readily identified on the surface of
C. parvum
oocysts by attenuated total reflectance-Fourier transform infrared spectroscopy, suggesting that these purification reagents may not be responsible for the stability of the uncharged oocysts. These findings imply that precipitate enmeshment may be the optimal mechanism of coagulation for removal of oocysts in water treatment systems. The results of this work may help elucidate the causes of variation in oocyst surface characteristics, may ultimately lead to improved removal efficiencies in full-scale water treatment systems, and may improve fate and transport predictions for oocysts in natural systems.
Production of Novel Tetrahydroxyfuranyl Fatty Acids from α-Linolenic Acid by
Clavibacter
sp. Strain ALA2
Authors: Hosokawa Masashi , Hou Ching T. , Weisleder David 
Published: July 2003

ABSTRACT

Previously, it was reported that a newly isolated microbial culture,
Clavibacter
sp. strain ALA2, produced trihydroxy unsaturated fatty acids, diepxoy bicyclic fatty acids, and tetrahydroxyfuranyl fatty acids (THFAs) from linoleic acid (C. T. Hou, J. Am. Oil Chem. Soc. 73:1359-1362, 1996; C. T. Hou and R. J. Forman III, J. Ind. Microbiol. Biotechnol. 24:275-276, 2000; C. T. Hou, H. Gardner, and W. Brown, J. Am. Oil Chem. Soc. 75:1483-1487, 1998; C. T. Hou, H. W. Gardner, and W. Brown, J. Am. Oil Chem. Soc. 78:1167-1169, 2001). In this study, we found that
Clavibacter
sp. strain ALA2 produced novel THFAs, including 13,16-dihydroxy-12-THFA, 15-epoxy-9(
Z
)-octadecenoic acid (13,16-dihydroxy-THFA), and 7,13,16-trihydroxy-12, 15-epoxy-9(
Z
)-octadecenoic acid (7,13,16-trihydroxy-THFA), from α-linolenic acid (9,12,15-octadecatrienoic acid). The chemical structures of these products were determined by gas chromatography-mass spectrometry and proton and
13
C nuclear magnetic resonance analyses. The optimum incubation temperature was 30°C for production of both hydroxy-THFAs. 13,16-Dihydroxy-THFA was detected after 2 days of incubation, and the concentration reached 45 mg/50 ml after 7 days of incubation; 7,13,16-trihydroxy-THFA was not detected after 2 days of incubation, but the concentration reached 9 mg/50 ml after 7 days of incubation. The total yield of both 13,16-dihydroxy-THFA and 7,13,16-trihydroxy-THFA was 67% (wt/wt) after 7 days of incubation at 30°C and 200 rpm. In previous studies, it was reported that
Clavibacter
sp. strain ALA2 oxidized the C-7, C-12, C-13, C-16, and C-17 positions of linoleic acid (n-6) into hydroxy groups. In this case, the bond between the C-16 and C-17 carbon atoms is saturated. In α-linolenic acid (n-3), however, the bond between the C-16 and C-17 carbon atoms is unsaturated. It seems that enzymes of strain ALA2 oxidized the C-12-C-13 and C-16-C-17 double bonds into dihydroxy groups first and then converted them to hydroxy-THFAs.
Isolation of Tetracycline-Resistant
Megasphaera elsdenii
Strains with Novel Mosaic Gene Combinations of
tet
(O) and
tet
(W) from Swine
Authors: Stanton Thaddeus B. , Humphrey Samuel B. 
Published: July 2003

ABSTRACT

Anaerobic bacteria insensitive to chlortetracycline (64 to 256 μg/ml) were isolated from cecal contents and cecal tissues of swine fed or not fed chlortetracycline. A nutritionally complex, rumen fluid-based medium was used for culturing the bacteria. Eight of 84 isolates from seven different animals were identified as
Megasphaera elsdenii
strains based on their large-coccus morphology, rapid growth on lactate, and 16S ribosomal DNA sequence similarities with
M. elsdenii
LC-1
T
. All eight strains had tetracycline MICs of between 128 and 256 μg/ml. Based on PCR assays differentiating 14
tet
classes, the strains gave a positive reaction for the
tet
(O) gene. By contrast, three ruminant
M. elsdenii
strains recovered from 30-year-old culture stocks had tetracycline MICs of 4 μg/ml and did not contain
tet
genes. The
tet
genes of two tetracycline-resistant
M. elsdenii
strains were amplified and cloned. Both genes bestowed tetracycline resistance (MIC = 32 to 64 μg/ml) on recombinant
Escherichia coli
strains. Sequence analysis revealed that the
M. elsdenii
genes represent two different mosaic genes formed by interclass (double-crossover) recombination events involving
tet
(O) and
tet
(W). One or the other genotype was present in each of the eight tetracycline-resistant
M. elsdenii
strains isolated in these studies. These findings suggest a role for commensal bacteria not only in the preservation and dissemination of antibiotic resistance in the intestinal tract but also in the evolution of resistance.
Anaerobic Transformation of Alkanes to Fatty Acids by a Sulfate-Reducing Bacterium, Strain Hxd3
Authors: So Chi Ming , Phelps Craig D. , Young L. Y. 
Published: July 2003

ABSTRACT

Strain Hxd3, an alkane-degrading sulfate reducer previously isolated and described by Aeckersberg et al. (F. Aeckersberg, F. Bak, and F. Widdel, Arch. Microbiol. 156:5-14, 1991), was studied for its alkane degradation mechanism by using deuterium and
13
C-labeled compounds. Deuterated fatty acids with even numbers of C atoms (C-even) and
13
C-labeled fatty acids with odd numbers of C atoms (C-odd) were recovered from cultures of Hxd3 grown on perdeuterated pentadecane and [1,2-
13
C
2
]hexadecane, respectively, underscoring evidence that C-odd alkanes are transformed to C-even fatty acids and vice versa. When Hxd3 was grown on unlabeled hexadecane in the presence of [
13
C]bicarbonate, the resulting 15:0 fatty acid, which was one carbon shorter than the alkane, incorporated a
13
C label to form its carboxyl group. The same results were observed when tetradecane, pentadecane, and perdeuterated pentadecane were used as the substrates. These observations indicate that the initial attack of alkanes includes both carboxylation with inorganic bicarbonate and the removal of two carbon atoms from the alkane chain terminus, resulting in a fatty acid one carbon shorter than the original alkane. The removal of two terminal carbon atoms is further evidenced by the observation that the [1,2-
13
C
2
]hexadecane-derived fatty acids contained either two
13
C labels located exclusively at their acyl chain termini or none at all. Furthermore, when perdeuterated pentadecane was used as the substrate, the 14:0 and 16:0 fatty acids formed both carried the same numbers of deuterium labels, while the latter was not deuterated at its carboxyl end. These observations provide further evidence that the 14:0 fatty acid was initially formed from perdeuterated pentadecane, while the 16:0 fatty acid was produced after chain elongation of the former fatty acid with nondeuterated carbon atoms. We propose that strain Hxd3 anaerobically transforms an alkane to a fatty acid through a mechanism which includes subterminal carboxylation at the C-3 position of the alkane and elimination of the two adjacent terminal carbon atoms.
Degradation of Benzo[
a
]pyrene by the Litter-Decomposing Basidiomycete
Stropharia coronilla
: Role of Manganese Peroxidase
Authors: Steffen Kari T. , Hatakka Annele , Hofrichter Martin 
Published: July 2003

ABSTRACT

The litter-decomposing basidiomycete
Stropharia coronilla
, which preferably colonizes grasslands, was found to be capable of metabolizing and mineralizing benzo[
a
]pyrene (BaP) in liquid culture. Manganese(II) ions (Mn
2+
) supplied at a concentration of 200 μM stimulated considerably both the conversion and the mineralization of BaP; the fungus metabolized and mineralized about four and twelve times, respectively, more of the BaP in the presence of supplemental Mn
2+
than in the basal medium. This stimulating effect could be attributed to the ligninolytic enzyme manganese peroxidase (MnP), whose activity increased after the addition of Mn
2+
. Crude and purified MnP from
S. coronilla
oxidized BaP efficiently in a cell-free reaction mixture (in vitro), a process which was enhanced by the surfactant Tween 80. Thus, 100 mg of BaP liter
−1
was converted in an in vitro reaction solution containing 1 U of MnP ml
−1
within 24 h. A clear indication was found that BaP-1,6-quinone was formed as a transient metabolite, which disappeared over the further course of the reaction. The treatment of a mixture of 16 different polycyclic aromatic hydrocarbons (PAHs) selected by the U.S. Environmental Protection Agency as model standards for PAH analysis (total concentration, 320 mg liter
−1
) with MnP resulted in concentration decreases of 10 to 100% for the individual compounds, and again the stimulating effect of Tween 80 was observed. Probably due to their lower ionization potentials, poorly bioavailable, high-molecular-mass PAHs such as BaP, benzo(
g
,
h
,
i
)perylene, and indeno(1,2,3-
c
,
d
)pyrene were converted to larger extents than low-molecular-mass ones (e.g., phenanthrene and fluoranthene).
Quantifying Mold Biomass on Gypsum Board: Comparison of Ergosterol and Beta-
N
-Acetylhexosaminidase as Mold Biomass Parameters
Authors: Reeslev M. , Miller M. , Nielsen K. F. 
Published: July 2003

ABSTRACT

Two mold species,
Stachybotrys chartarum
and
Aspergillus versicolor
, were inoculated onto agar overlaid with cellophane, allowing determination of a direct measurement of biomass density by weighing. Biomass density, ergosterol content, and beta-
N
-acetylhexosaminidase (3.2.1.52) activity were monitored from inoculation to stationary phase. Regression analysis showed a good linear correlation to biomass density for both ergosterol content and beta-
N
-acetylhexosaminidase activity. The same two mold species were inoculated onto wallpapered gypsum board, from which a direct biomass measurement was not possible. Growth was measured as an increase in ergosterol content and beta-
N
-acetylhexosaminidase activity. A good linear correlation was seen between ergosterol content and beta-
N
-acetylhexosaminidase activity. From the experiments performed on agar medium, conversion factors (CFs) for estimating biomass density from ergosterol content and beta-
N
-acetylhexosaminidase activity were determined. The CFs were used to estimate the biomass density of the molds grown on gypsum board. The biomass densities estimated from ergosterol content and beta-
N
-acetylhexosaminidase activity data gave similar results, showing significantly slower growth and lower stationary-phase biomass density on gypsum board than on agar.
Temporal Stability and Biodiversity of Two Complex Antilisterial Cheese-Ripening Microbial Consortia
Authors: Maoz Ariel , Mayr Ralf , Scherer Siegfried 
Published: July 2003

ABSTRACT

The temporal stability and diversity of bacterial species composition as well as the antilisterial potential of two different, complex, and undefined microbial consortia from red-smear soft cheeses were investigated. Samples were collected twice, at 6-month intervals, from each of two food producers, and a total of 400 bacterial isolates were identified by Fourier-transform infrared spectroscopy and 16S ribosomal DNA sequence analysis. Coryneform bacteria represented the majority of the isolates, with certain species being predominant. In addition,
Marinolactobacillus psychrotolerans
,
Halomonas venusta
,
Halomonas variabilis
,
Halomonas
sp. (10
6
to 10
7
CFU per g of smear), and an unknown, gram-positive bacterium (10
7
to 10
8
CFU per g of smear) are described for the first time in such a consortium. The species composition of one consortium was quite stable over 6 months, but the other consortium revealed less diversity of coryneform species as well as less stability. While the first consortium had a stable, extraordinarily high antilisterial potential in situ, the antilisterial activity of the second consortium was lower and decreased with time. The cause for the antilisterial activity of the two consortia remained unknown but is not due to the secretion of soluble, inhibitory substances by the individual components of the consortium. Our data indicate that the stability over time and a potential antilisterial activity are individual characteristics of the ripening consortia which can be monitored and used for safe food production without artificial preservatives.
Mutants and Intersexual Heterokaryons of
Blakeslea trispora
for Production of β-Carotene and Lycopene
Authors: Mehta Bina J. , Obraztsova Irina N. , Cerdá-Olmedo Enrique 
Published: July 2003

ABSTRACT

The industrial production of β-carotene with the zygomycete
Blakeslea trispora
involves the joint cultivation of mycelia of opposite sex in the presence of β-ionone and other chemical activators. We have obtained improved strains by mutation and heterokaryosis. We chose wild strains on the basis of their growth and carotene content in single and mated cultures. Following exposure of their spores to
N
-methyl-
N
′-nitro-
N
-nitrosoguanidine, we obtained high-carotene mutants, which were more productive than their parents but similar to them in having β-carotene as the main product. Further increases in carotene content were obtained after a new round of mutagenesis in one of the mutants. The production was shifted to lycopene in cultures incubated in the presence of nicotine and in lycopene-rich mutants derived from the wild strains. The highest production levels were achieved in intersexual heterokaryons, which contained mutant nuclei of opposite sex. These contained up to 39 mg of β-carotene or 15 mg of lycopene per g (dry mass) under standard laboratory conditions in which the original wild strains contained about 0.3 mg of β-carotene per g (dry mass). β-Ionone did not increase the carotene content of these strains. Not all wild strains lent themselves to these improvements, either because they produced few mutants or because they did not increase their carotene production in mated cultures.
Toxicity of Al to
Desulfovibrio desulfuricans
Authors: Amonette J. E. , Russell C. K. , Carosino K. A. , Robinson N. L. , Ho J. T. 
Published: July 2003

ABSTRACT

The toxicity of Al to
Desulfovibrio desulfuricans
G20 was assessed over a period of 8 weeks in a modified lactate C medium buffered at four initial pHs (5.0, 6.5, 7.2, and 8.3) and treated with five levels of added Al (0, 0.01, 0.1, 1.0, and 10 mM). At pH 5, cell population densities decreased significantly and any effect of Al was negligible compared to that of the pH. At pHs 6.5 and 7.2, the cell population densities increased by 30-fold during the first few days and then remained stable for soluble-Al concentrations of <5 × 10
−5
M. In treatments having total-Al concentrations of ≥1 mM, soluble-Al concentrations exceeded 5 × 10
−5
M and limited cell population growth substantially and proportionally. At pH 8.3, soluble-Al concentrations were below the 5 × 10
−5
M toxicity threshold and cell population density increases of 20- to 40-fold were observed. An apparent cell population response to added Al at pH 8.3 was attributed to the presence of large, spirilloidal bacteria (accounting for as much as 80% of the cells at the 10 mM added Al level). Calculations of soluble-Al speciation for the pH 6.5 and 7.2 treatments that showed Al toxicity suggested the possible presence of the Al
13
O
4
(OH)
24
(H
2
O)
12
7+
“tridecamer” cation and an inverse correlation of the tridecamer concentration and the cell population density. Analysis by
27
Al nuclear magnetic resonance spectroscopy, however, yielded no evidence of this species in freshly prepared samples or those taken 800 days after inoculation. Exclusion of the tridecamer species from the aqueous speciation calculations at pHs 6.5 and 7.2 yielded inverse correlations of the neutral Al(OH)
3
and anionic Al(OH)
4
−
monomeric species with cell population density, suggesting that one or both of these ions bear primary responsibility for the toxicity observed.