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New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
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Archives of Microbiology (v.192, #12)
Effects of the antibiotic growth promoters flavomycin and florfenicol on the autochthonous intestinal microbiota of hybrid tilapia (Oreochromis niloticus ♀ × O. aureus ♂) by Suxu He; Zhigang Zhou; Yuchun Liu; Yanan Cao; Kun Meng; Pengjun Shi; Bin Yao; Einar Ringø (pp. 985-994).
The 16S rDNA PCR-DGGE and rpoB quantitative PCR (RQ-PCR) techniques were used to evaluate the effects of dietary flavomycin and florfenicol on the autochthonous intestinal microbiota of hybrid tilapia. The fish were fed four diets: control, dietary flavomycin, florfenicol and their combination. After 8 weeks of feeding, 6 fish from each cage were randomly chosen for the analysis. The total number of intestinal bacteria was determined by RQ-PCR. The results showed that dietary antibiotics significantly influenced the intestinal microbiota and dramatically reduced the intensity of total intestinal bacterial counts. The intensity of some phylotypes (EU563257, EU563262 and EU563255) were reduced to non-detectable levels by both dietary antibiotics, while supplementation of florfenicol to the diet also reduced the intensity of the phylotypes EU563242 and EU563262, uncultured Mycobacterium sp.-like, uncultured Cyanobacterium-like and uncultured Cyanobacterium (EU563246). Dietary flavomycin only reduced the OTU intensity of one phylotype, identified as a member of the phylum Fusobacteria. The antibiotic combination only reduced the phylotypes EU563242 and EU563262. Based on our results, we conclude that the reduced effect of florfenicol on intestinal microbiota was stronger than that of flavomycin, and when flavomycin and florfenicol were added in combination, the effect of florfenicol overshadowed that of flavomycin.
Keywords: Hybrid tilapia; Dietary flavomycin; Florfenicol; RQ-PCR; DGGE; Intestinal bacteria
Evaluation of in vitro antagonism and of in vivo immune modulation and protection against pathogenic experimental challenge of two probiotic strains of Bifidobacterium animalis var. lactis by Ariane K. S. Martins; Flaviano S. Martins; Danielle A. Gomes; Samir D. A. Elian; Angélica T. Vieira; Mauro M. Teixeira; Denise C. Cara; Regina M. D. Nardi; Jacques R. Nicoli (pp. 995-1003).
The aim of the present study was to compare the effect of intragastric administration with two strains of Bifidobacterium animalis subsp. lactis (Bifido A and Bifido B), in gnotobiotic and conventional mice, challenged with Salmonella Typhimurium. In vitro antagonism test showed that the two strains were able to produce antagonistic substances against various pathogenic microorganisms. In an ex vivo antagonism test the production of antagonistic substances was observed only against three out ten pathogens tested. Both Bifidobacterium strains were able to colonize and to maintain high population levels in the digestive tract of gnotobiotic mice. In addition, the two strains had low and limited translocation ability and did not cause any histological lesion in any of the organs analyzed. Both strains were able to reduce the fecal number of Salmonella in gnotobiotic mice challenged with the pathogen, but only Bifido B was able to confer a protection as demonstrated by a lower mortality. Higher levels of sIgA and IL-10 were observed only in Bifido B mono-associated mice when compared to germ free group. We could conclude that, among the parameters analyzed, the strain Bifido B exhibited the more desirable characteristics to be used as a probiotic.
Keywords: Probiotics; Bifidobacterium animalis subsp. lactis ; Salmonella enterica serovar Typhimurium; Translocation; sIgA; IL-10
Membrane fluidity and fatty acid comparisons in psychrotrophic and mesophilic strains of Acidithiobacillus ferrooxidans under cold growth temperatures by Nadia C. S. Mykytczuk; Jack T. Trevors; Susan M. Twine; Garry D. Ferroni; Leo G. Leduc (pp. 1005-1018).
Psychrotrophic strains of Acidithiobacillus ferrooxidans have an important role in metal leaching and acid mine drainage (AMD) production in colder mining environments. We investigated cytoplasmic membrane fluidity and fatty acid alterations in response to low temperatures (5 and 15°C). Significant differences in membrane fluidity, measured by polarization (P) of 1,6-diphenyl-1,3,5-hexatriene (DPH), were found where the psychrotrophic strains had a significantly more rigid membrane (P range = 0.41–0.45) and lower transition temperature midpoints (T m = 2.0°C) and broader transition range than the mesophilic strains (P range = 0.38–0.39; T m = 2.0–18°C) at cold temperatures. Membrane remodeling was evident in all strains with a common trend of increased unsaturated fatty acid component in response to lower growth temperatures. In psychrotrophic strains, decreases in 12:0 fatty acids distinguished the 5°C fatty acid profiles from those of the mesophilic strains that showed decreases in 16:0, 17:0, and cyclo-19:0 fatty acids. These changes were also correlated with the observed changes in membrane fluidity (R 2 = 63–97%). Psychrotrophic strains employ distinctive modulation of cytoplasmic membrane fluidity with uncommon membrane phase changes as part of their adaptation to the extreme AMD environment in colder climates.
Keywords: Acid mine drainage; Acidithiobacillus ferrooxidans ; Adaptation; Cold stress; Membrane fluidity
Inhibition of Vibrio cholerae biofilm by AiiA enzyme produced from Bacillus spp. by Nimmy Augustine; Praveen Kumar; Sabu Thomas (pp. 1019-1022).
Vibrio cholerae is the causative agent of water-borne diarrheal disease, cholera. The formation of biofilm favors survival and persistence of V. cholerae in the aquatic environment and also inside the host. AHL lactonase (AiiA), a metallo-beta-lactamase produced by Bacillus spp., blocks quorum sensing in Gram-negative bacteria by hydrolyzing N-acyl-homoserine lactones (AHLs). In the present investigation, AiiA-mediated inhibition of V. cholerae biofilm was studied. Two novel alleles of aiiA-encoding genes from Bacillus spp. were expressed in E. coli, and the results demonstrated that AiiA enzyme is a potent inhibitor of V. cholerae biofilm.
Keywords: AiiA enzyme; Biofilm; Quorum sensing; V. cholerae
Modelling the effect of the physical and chemical characteristics of the materials used as casing layers on the production parameters of Agaricus bisporus by Arturo Pardo; J. Emilio Pardo; J. Arturo de Juan; Diego Cunha Zied (pp. 1023-1030).
The aim of this research was to show the mathematical data obtained through the correlations found between the physical and chemical characteristics of casing layers and the final mushrooms’ properties. For this purpose, 8 casing layers were used: soil, soil + peat moss, soil + black peat, soil + composted pine bark, soil + coconut fibre pith, soil + wood fibre, soil + composted vine shoots and, finally, the casing of La Rioja subjected to the ruffling practice. The conclusion that interplays in the fructification process with only the physical and chemical characteristics of casing are complicated was drawn. The mathematical data obtained in earliness could be explained in non-ruffled cultivation. The variability observed for the mushroom weight and the mushroom diameter variables could be explained in both ruffled and non-ruffled cultivations. Finally, the properties of the final quality of mushrooms were established by regression analysis.
Keywords: Agaricus bisporus ; Casing layer; Physical and chemical characteristics; Regression analysis; Yield
Identification and regulation of novel compatible solutes from hypersaline stromatolite-associated cyanobacteria by Falicia Goh; Kevin D. Barrow; Brendan P. Burns; Brett A. Neilan (pp. 1031-1038).
Cyanobacteria are able to survive in various extreme environments via the production of organic compounds known as compatible solutes. In particular, cyanobacteria are capable of inhabiting hypersaline environments such as those found in intertidal regions. Cyanobacteria in these environments must possess regulatory mechanisms for surviving the changing osmotic pressure as a result of desiccation, rainfall and tidal fluxes. The objective of this study was to determine the compatible solutes that are accumulated by cyanobacteria from hypersaline regions, and specifically, the stromatolite ecosystems of Shark Bay, Western Australia. Previously, the cyanobacterial populations associated with these stromatolites were characterized in two separate studies. Compatible solutes were extracted from isolated cyanobacteria here and identified by nuclear magnetic resonance. As the media of isolation contained no complex carbon source, the solutes accumulated were likely synthesized by the cyanobacteria. The data indicate that from this one habitat taxonomically distinct cyanobacteria exposed to varying salinities accumulate a range of known compatible solutes. In addition, taxonomically similar cyanobacteria do not necessarily accumulate the same compatible solutes. Glucosylglycerol, a compatible solute unique to marine cyanobacteria was not detected; however, various saccharides, glycine betaine, and trimethylamine-N-oxide were identified as the predominant solutes. We conclude that the cyanobacterial communities from these hypersaline stromatolites are likely to possess more complex mechanisms of adaptation to osmotic stress than previously thought. The characterization of osmoregulatory properties of stromatolite microorganisms provides further insight into how life can thrive in such extreme environments.
Keywords: Cyanobacteria; Salt tolerance; Compatible solutes; Osmolytes
Characterization of Edwardsiella tarda waaL: roles in lipopolysaccharide biosynthesis, stress adaptation, and virulence toward fish by Lili Xu; Qiyao Wang; Jingfan Xiao; Qin Liu; Xin Wang; Tao Chen; Yuanxing Zhang (pp. 1039-1047).
Edwardsiella tarda is the causative agent of edwardsiellosis in fish. The genome sequence of a virulent strain EIB202 has been determined. According to the genome sequence, the lipopolysaccharide (LPS) synthesis cluster containing a putative O-antigen ligase gene waaL was identified. Here, the in-frame deletion mutant ΔwaaL was constructed to analyze the function of WaaL in E. tarda EIB202. The ΔwaaL mutant displayed absence in O-antigen side chains in the LPS production. The ΔwaaL mutant exhibited an increased sensitivity to hydrogen peroxide indicating that the LPS was involved in the endurance to the oxidative stress in hosts during infection. In addition, the resistance of ΔwaaL to serum and polymyxin B decreased remarkably. The ΔwaaL mutant was also attenuated in virulence, showed an impaired ability in internalization of epithelioma papulosum cyprinid (EPC) cells and a comparatively poor ability of proliferation in vivo, which was in line with the increased LD50 value. These results indicated that waaL gene was a functional member of the gene cluster involved in LPS synthesis and highlighted the importance of the O-antigen side chains to stress adaption and virulence in E. tarda, signifying the gene as a potential target for live attenuated vaccine against this bacterium.
Keywords: Edwardsiella tarda ; WaaL; Lipopolysaccharide; Stress adaption; Virulence
Production, purification and structural characterization of an exopolysaccharide produced by a probiotic Lactobacillus plantarum MTCC 9510 by Bindhumol Ismail; Kesavan Madhavan Nampoothiri (pp. 1049-1057).
Exopolysaccharides (EPS) from lactic acid bacteria contribute to specific rheology and texture of fermented milk products and finds applications even in non-dairy foods and in therapeutics. Box-Behnken model of response surface methodology (RSM) was employed to formulate the production medium for exopolysaccharide (EPS). FT-IR spectral analysis of the purified EPS from Lactobacillus plantarum MTCC 9510 revealed prominent characteristic groups corresponding to polyhydric alcohols. The degradation temperature (Td) of the polysaccharide was found to be 260°C with the help of thermo gravimetric analysis (TGA). Structure elucidation of the EPS showed that it consists of a trisaccharide repeating unit of α-d-glucose, β-d-glucose and α-d-mannose.
Keywords: Exopolysaccharides; Fourier transform infrared; Lactobacillus plantarum ; Nuclear magnetic resonance spectroscopy; Probiotics; Thermogravimetry
The sensitivity of Bacillus subtilis to diverse antimicrobial compounds is influenced by Abh by Ewan J. Murray; Nicola R. Stanley-Wall (pp. 1059-1067).
Abh is a transition state regulator of Bacillus subtilis that controls biofilm formation and the production of several diverse antimicrobial compounds. Using a high-throughput non-biased technique, we show for the first time that Abh influences the sensitivity of B. subtilis to diverse antimicrobial compounds. Following up on these findings with a combination of classical genetics and antibiotic susceptibility assays, we demonstrate that Abh influences cellular processes such as the remodelling of the cell wall. We present data demonstrating that the extracytoplasmic function sigma factor σX controls resistance to β-lactam antibiotics by activating abh transcription. Downstream from Abh, activation of slrR expression by Abh is responsible for controlling the sensitivity of B. subtilis to such antibiotics due to the role that SlrR plays in regulating autolysin biosynthesis. The abh mutant additionally exhibits increased resistance to aminoglycoside antimicrobials. We confirm that aminoglycoside killing of B. subtilis is likely to be caused by oxidative damage but rule out the possibility that the increased resistance of the abh mutant to aminoglycosides is due to a general increase in resistance to oxidative stress.
Keywords: Bacillus subtilis ; Antibiotic sensitivity; Abh; AbrB