Canadian journal of microbiology最新文献

Bifidobacterium and Lactobacillus are known to be common members of the human intestinal microbiota, which play important roles in maintaining the homeostasis of host gut microenvironment. Several bifidobacterial and lactobacilli strains have been used as probiotics for health benefits. The exopolysaccharides (EPSs) produced by strains from Bifidobacterium and Lactobacillus are considered as beneficial traits mediating these beneficial effects. In this study, 21 strains belonging to Bifidobacterium and Lactobacillus were isolated from healthy infants' stool and were screened for EPS-producing ability. Among these strains, Bifidobacterium longum XZM1 showed the highest EPS productivity, which was further confirmed and characterized. The complete genome of strain XZM1 was sequenced, which revealed the presence of a gene cluster for EPS production. Furthermore, comparative genome analysis was performed among XZM1 and other strains from B. longum species. Following purification, the molecular weight (Mw) of EPS from XZM1 was determined as 4023 Da (Mw) through gel permeation chromatography. Analysis of the EPS hydrolysates revealed that the EPS was composed of mannose, glucose, galactose, arabinose, and fucose. Additionally, the EPS exhibited higher scavenging abilities toward hydroxyl than 1,1-diphenyl-2-picrylhydrazyl free radical. Overall, these results suggest that XZM1 from B. longum species may be a promising probiotic candidate.

The type VI secretion system (T6SS) is used by bacteria for virulence, resistance to grazing, and competition with other bacteria. We previously demonstrated that the role of the T6SS in interbacterial competition and in resistance to grazing is enhanced in Vibrio cholerae in the presence of subinhibitory concentrations of polymyxin B. Here, we performed a global quantitative proteomic analysis and a targeted transcriptomic analysis of the T6SS-known regulators in V. cholerae grown with and without polymyxin B. The proteome of V. cholerae is greatly modified by polymyxin B with more than 39% of the identified cellular proteins displaying a difference in their abundance, including T6SS-related proteins. We identified a regulator whose abundance and expression are increased in the presence of polymyxin B, vxrB, the response regulator of the two-component system VxrAB (VCA0565-66). In vxrAB, vxrA and vxrB deficient mutants, the expression of both hcp copies (VC1415 and VCA0017), although globally reduced, was not modified by polymyxin B. These hcp genes encode an identical protein Hcp, which is the major component of the T6SS syringe. Thus, the upregulation of the T6SS in the presence of polymyxin B appears to be, at least in part, due to the two-component system VxrAB.

Endophytes confer fitness advantages to host plants. However, the ecological communities of endophytic fungi in the different tissues (rhizomes, stems, and leaves) of Paris polyphylla and the relationship of their endophytic fungi with polyphyllin levels remain unclear. In this study, the community diversity and differences of endophytic fungi in the rhizomes, stems, and leaves of P. polyphylla var. yunnanensis were investigated, and a comprehensively diverse community of endophytic fungi was represented, including 50 genera, 44 families, 30 orders, 12 classes, and 5 phyla. Distributions of endophytic fungi differed greatly across the three tissues, with six genera common to all tissues, and 11, 5, and 4 genera specific to the rhizomes, stems, and leaves, respectively. Seven genera showed a significantly positive correlation to polyphyllin contents, indicating their potential roles in polyphyllin accumulation. This study provides valuable information for further research of the ecological and biological functions of endophytic fungi of P. polyphylla.

The goal of this study was to (a) determine the minimum selection concentrations of tetracycline family antibiotics necessary to maintain plasmids carrying tetracycline-resistant genes and (b) correlate these results to environmental hotspot concentrations reported in previous studies. This study used two plasmids (pT295A and pT413A) originating from dairy manure in a surrogate Escherichia coli host CV601. The minimum selection concentrations of antibiotics tested in nutrient-rich medium were determined as follows: 0.1 mg/L for oxytetracycline, 0.45 mg/L for chlortetracycline, and 0.13-0.25 mg/L for tetracycline. Mixing oxytetracycline and chlortetracycline had minimum selection concentration values increased 2-fold compared to those in single antibiotic tests. Minimum selection concentrations found in this study were lower than reported environmental hotspot concentrations, suggesting that tetracycline family antibiotics were likely to be the driver for the selection and maintenance of these plasmids. Relatively high plasmid loss rates (>90%) were observed when culturing a strain carrying a tetracycline-resistant plasmid in antibiotic-free nutrient-rich and nutrient-defined media. Overall, results suggested that these plasmids can be maintained at concentrations environmentally relevant in wastewater treatment plants, sewage, manure, and manured soil; however, they are unstable and easily lost in the absence of antibiotics.

Antibiotic overuse and misuse have promoted the emergence and spread of antibiotic-resistant bacteria. Increasing bacterial resistance to antibiotics is a major healthcare problem, necessitating elucidation of antibiotic resistance mechanisms. In this study, we explored the mechanism of gentamicin resistance by comparing the transcriptomes of antibiotic-sensitive and -resistant Escherichia coli. A total of 410 differentially expressed genes were identified, of which 233 (56.83%) were up-regulated and 177 (43.17%) were down-regulated in the resistant strain compared with the sensitive strain. Gene Ontology (GO) analysis classifies differential gene expression into three main categories: biological processes, cellular components, and molecular functions. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that the up-regulated genes were enriched in eight metabolic pathways, including fatty acid metabolism, which suggests that fatty acid metabolism may be involved in the development of gentamicin resistance in E. coli. This was demonstrated by measuring the acetyl-CoA carboxylase activity, plays a fundamental role in fatty acid metabolism, was increased in gentamicin-resistant E. coli. Treatment of fatty acid synthesis inhibitor, triclosan, promoted gentamicin-mediated killing efficacy to antibiotic-resistant bacteria. We also found that exogenous addition of oleic acid, which involved in fatty acid metabolism, reduced E. coli sensitivity to gentamicin. Overall, our results provide insight into the molecular mechanism of gentamicin resistance development in E. coli.

Anaerobic microorganisms in Canada Natural Upgrading Limited (CNUL) fluid fine tailings (FFT) are sustained by residual solvent hydrocarbons. Although FFT are methanogenic in nature, sulfate-reducing microorganisms represent a significant portion of FFT bacterial community. In this study, we examined biodegradation of three iso-alkanes (2-methylbutane, 2-methylpentane, and 3-methylpentane), representing major iso-alkanes in paraffinic solvent, in CNUL FFT under sulfate-reducing conditions. During ∼1100 days of incubation, only 2-methylpentane was degraded partially, whereas 2-methylbutane and 3-methylpentane were not degraded. During active degradation of 2-methylpentane, the bacterial community was dominated by Anaerolineaceae followed by Syntrophaceae, Peptococcaceae, Desulfobacteraceae, and Desulfobulbaceae. The archaeal community was co-dominated by acetoclastic (Methanosaetaceae) and hydrogenotrophic (Methanobacteriaceae) methanogens. This study underlines the limited capability of the microbial community indigenous to CNUL FFT in degrading recalcitrant iso-alkanes under sulfate-reducing conditions.

Endophytic bacteria play crucial roles in the growth and bioactive compound synthesis of host plants. In this study, the composition and diversity of endophytic bacteria in the roots, stems, and leaves from 3-year-old artificially cultivated Huperzia serrata were investigated using Illumina HiSeq sequencing technology. Total effective reads were assigned to 936 operational taxonomic units (OTUs), belonging to 12 phyla and 289 genera. A total of 28, 3, and 2 OTUs were exclusive to the roots, stems, and leaves, respectively. The bacterial richness and diversity in the roots were significantly lower than those in the leaves and stems. The dominant genera with significant distribution differences among these plant tissue samples were Burkholderia-Caballeronia-Paraburkholderia, Sphingomonas, Acidibacter, Bradyrhizobium, Bryobacter, Methylocella, Nocardioides, Acidothermus, and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium. Furthermore, the differences in the bacterial communities associated with these plant tissue samples were visualized using principal coordinate analysis and cluster pedigree diagrams. Linear discriminant analysis effect size explained statistically significant differences among the endophytic bacterial microbiota in these plant tissue samples. Overall, this study provides new insights into the diversity and distribution patterns of endophytic bacteria in the different tissues of H. serrata.

In this paper, high-throughput sequencing technology was adopted to visualize the microbial communities on the surfaces of two types of carbon steel immersed in Sea Area Ⅰ. The results showed that different microbial communities were formed on different carbon steel surfaces, in which the genus with the highest abundance on the surface of Q235 was Escherichia-Shigella, while anaerobic Desulfovibrio on the surface of 921a was the most abundant, and the dominant genus varied with the depth of the rust layer. In addition, the distribution of sulfate-reducing bacteria (SRB) on the surface of Q235 submerged in Sea Area Ⅱ was compared with the sulfate-reducing bacteria's distribution in Sea Area Ⅰ, using the environmental factors correlation analysis. The results showed that the concentrations of Ca²⁺, Na⁺, K⁺, Mg²⁺, and Al³⁺ were positively correlated with the distribution of SRB, while the concentrations of Cu²⁺, Zn²⁺, SO₄ ^2-, Cl^-, NO₃ ^-, and organic carbon were negatively correlated with it. Furthermore, there was a highly significant correlation between each geochemical factor and Desulfotomaculum (p < 0.01).

Using endophytic fungal elicitors to increase the accumulation of valuable secondary metabolites in plant tissue culture is an effective biotechnology strategy. In this study, a collection of 56 strains of endophytic fungi were isolated from different organs of cultivated Panax ginseng, of which seven strains can be symbiotically co-cultured with the hairy roots of P. ginseng. Further experiments observed that strain 3R-2, identified as endophytic fungus Schizophyllum commune, can not only infect hairy roots but also promote the accumulation of specific ginsenosides. This was further verified because S. commune colonization significantly affected the overall metabolic profile of ginseng hairy roots. By comparing the effects of S. commune mycelia and its mycelia extract (EM) on ginsenoside production in P. ginseng hairy roots, the EM was confirmed to be a relatively better stimulus elicitor. Additionally, the introduction of EM elicitor can significantly enhance the expressions of key enzyme genes of pgHMGR, pgSS, pgSE, and pgSD involved in the biosynthetic pathway of ginsenosides, which was deemed the most relevant factor for promoting ginsenosides production during the elicitation period. In conclusion, this study is the first to show that the EM of endophytic fungus S. commune can be considered as an effective endophytic fungal elicitor for increasing the biosynthesis of ginsenosides in hairy root cultures of P. ginseng.

Hamilton Harbour is an impaired embayment of Lake Ontario that experiences seasonal algal blooms despite decades of remedial efforts. To study the harbour's cyanobacterial and heterotrophic bacterial communities, we extracted and sequenced community DNA from surface water samples collected biweekly from different sites during summer and fall. Assembled contigs were annotated at the phylum level, and Cyanobacteria were further characterized at order and species levels. Actinobacteria were most abundant in early summer, while Cyanobacteria were dominant in mid-summer. Microcystis aeruginosa and Limnoraphis robusta were most abundant throughout the sampling period, expanding the documented diversity of Cyanobacteria in Hamilton Harbour. Functional annotations were performed using the MG-RAST pipeline and SEED database, revealing that genes for photosynthesis, nitrogen metabolism, and aromatic compound metabolism varied in relative abundances over the season, while phosphorus metabolism was consistent, suggesting that these genes remained essential despite fluctuating environmental conditions and community succession. We observed seasonal shifts from anoxygenic to oxygenic phototrophy, and from ammonia assimilation to nitrogen fixation, coupled with decreasing heterotrophic bacteria and increasing Cyanobacteria relative abundances. Our data contribute important insights into bacterial taxa and functional potentials in Hamilton Harbour, revealing seasonal and spatial dynamics that can be used to inform ongoing remediation efforts.