Fluctuation in recoverable nickel and zinc resistant copiotrophic bacteria explained by the varying zinc ion content of Torsa River in different months

Inducible boron resistance via active efflux in Lysinibacillus and Enterococcus isolates from boron-contaminated agricultural soil

Phylogenetically diverse bacteria tolerate high boron concentrations while others require it for metabolic purposes despite the metalloid being toxic beyond a threshold. Boron resistance and plant growth promoting attributes of two bacterial strains, Lysinibacillus sp. OL1 and a novel Enterococcus sp. OL5, isolated from boron-fertilizer-amended cauliflower fields were investigated in this study. OL1 and OL5 grew efficiently in the presence of 210-230 mM boron, and resistance was found to be inducible by small amounts of the element: 5 to 50 mM boron pre-exposure progressively shortened the lag phase of growth in the presence of 200 mM boron. Intracellular boron accumulation was also found to be regulated by the level of pre-exposure: no induction or induction by small amounts led to higher levels of intracellular accumulation, whereas induction by high concentrations led to lower accumulation. These data, in the context of the strains' overall resistance towards 200 mM boron, indicated that induction by higher boron concentrations turned potential efflux mechanisms on, while resistance was eventually achieved by continuous cellular entry and exit of the ions. Involvement of solute efflux in boron resistance was corroborated by the genome content of the isolates (genes encoding proteins of the ATP-binding cassette, major facilitator, small multidrug resistance, multi antimicrobial extrusion, and resistance-nodulation-cell division, family/superfamily). Bacteria such as OL1 and OL5, which resist boron via influx-efflux, potentially lower boron bioavailability, and therefore toxicity, for the soil microbiota at large. These bacteria, by virtue of their plant-growth-promoting attributes, can also be used as biofertilizers.

Spatial biodiversity of bacteria along the largest Arctic river determined by next-generation sequencing

The biodiversity of bacterial communities along the Yenisei River at section c. 1800 km was studied using next-generation sequencing of 16S rRNA genes and common biodiversity indices. Overall, 3022 unique operational taxonomic units were identified. Actinobacteria and Proteobacteria were the dominant phyla at all sampling sites. The highest alpha-diversity values were found in the middle section of the studied river. The beta-diversity of bacterial assemblages in the river was related to the surrounding landscape (biome): three distinctly different bacterial assemblages occurred in sections of the river, situated in mountain taiga, plain taiga and in a region of permafrost, covered by forest-tundra and tundra. Tributaries arising from these different landscapes likely contributed substantially to the variations of Yenisei bacterial communities. In contrast to a prediction of the river continuum concept, the proportion of photoautotrophic Cyanobacteria in bacterial assemblages did not increase downstream, but peaked at the middle section.

Five novel acid-tolerant oligotrophic thiosulfate-metabolizing chemolithotrophic acid mine drainage strains affiliated with the genus Burkholderia of Betaproteobacteria and identification of two novel soxB gene homologues

Five acid-tolerant thiosulfate-metabolizing bacteria were isolated from acid mine drainage samples from Garubathan, India. 16S rRNA gene analysis revealed that the strains were affiliated with the genus Burkholderia of the class of Betaproteobacteria. Comparative 16S rRNA gene sequence analyses indicated that the strains designated as GAH1 and GAH2 produced a separate phylogenetic branch having Burkholderia pyrrocinia ATCC 51958(T) (96-98%) as the closest relative. Strains GAH4 and Burkholderia tropica Ppe8(T) (93%) branched out separately in the phylogenetic tree. Strain GMX2 was most closely related to Burkholderia cepacia ATCC 25417(T) (99.6%) and Burkholderia vietnamiensis LMG 10929(T) (99%). Strain GAH5 was most closely related to B. pyrrocinia ATCC 51958(T) (98%). Oligotrophy has been demonstrated in all AMD strains of Burkholderia spp. All strains showed chemolithoautotrophic and mixotrophic growth in thiosulfate. Furthermore, cell-free extracts of all test strains possessed thiosulfate and sulfite dehydrogenase activities. Phylogenetic analysis of the soxB gene revealed that GAH4 and GAH2 strains formed a novel cluster, Betaproteobacteria II, having highest similarity with Allochromatium vinosum, a member of Gammaproteobacteria II.