Taxonomically-linked growth phenotypes during arsenic stress among arsenic resistant bacteria isolated from soils overlying the Centralia coal seam fire

Abstract

Arsenic (As), a toxic element, has impacted life since early Earth. Thus, microorganisms have evolved many As resistance and tolerance mechanisms to improve their survival outcomes given As exposure. We isolated As resistant bacteria from Centralia, PA, the site of an underground coal seam fire that has been burning since 1962. From a 57.4°C soil collected from a vent above the fire, we isolated 25 unique aerobic As resistant bacterial strains spanning seven genera. We examined their diversity, resistance gene content, transformation abilities, inhibitory concentrations, and growth phenotypes. Although As concentrations were low at the time of soil collection (2.58 ppm), isolates had high minimum inhibitory concentrations (MICs) of arsenate and arsenite (>300 mM and 20 mM respectively), and most isolates were capable of arsenate reduction. We screened isolates (PCR and sequencing) using 12 published primer sets for six As resistance genes (AsRGs). Genes encoding arsenate reductase (arsC) and arsenite efflux pumps (arsB, ACR3(2)) were present, and phylogenetic incongruence between 16S rRNA genes and AsRGs provided evidence for horizontal gene transfer. A detailed investigation of differences in isolate growth phenotypes across As concentrations (lag time to exponential growth, maximum growth rate, and maximum OD590) showed a relationship with taxonomy, providing information that could help to predict an isolate’s performance given As exposure in situ. Our results suggest that microbiological management and remediation of environmental As could be informed by taxonomically-linked As tolerance, potential for resistance gene transferability, and the rare biosphere.

Arsenic‐tolerant microbial consortia from sediments of Copahue geothermal system with potential applications in bioremediation

“…Finally, it is worth noticing that both arsenate reductase (codified by arrA or arsC genes) only amplified in cultures supplemented with As(III), and that the amplifications of two forms of the primers that codified for the arsenite oxidase was observed in the anaerobic culture supplemented with arsenate Ana(As 5+ 50 mM). Our results, together with other related studies, prove the need to increase the knowledge of microbial resistance mechanisms to improve the design of primers, not only for the characterization of species but, more importantly, to enable the use of specific resistance genes as markers of As environmental contamination .…”

“…Even though our results are only preliminary, they show that in presence of As the tolerant consortia maintain acceptable µ values and reach approximately the same cellular concentrations than As‐free cultures, both desirable characteristic for the design of a bioremediation process. On this subject, it has been reported that microorganisms which develop faster might be better suited to cope with As contamination than those that present high Minimum Inhibitory Concentration (MIC) values .…”

“…Moreover, the arsenite oxidase is encoded by aio genes which are phylogenetically and ecologically widespread in bacteria and archaea , these aio genes have been amplified from environmental samples with very low levels of As contamination showing that As‐oxidizing microorganisms are quite ubiquitous . Microorganisms that develop in environments exposed to fluctuating As concentration or in areas which have had high As levels in the past are specially interesting to study and their specialized metabolisms have been proposed as a viable As bioremediation strategy as well as for others biotechnological applications; moreover, natural environments exposed to As have been the source of this microorganisms able to tolerate and metabolize As compounds .…”

Understanding Microbiome Stability in a Changing World

“…Given this complexity, my lab advances multiple research directions. Our toolbox includes high-throughput omics (mainly sequencing and metabolomics), in situ field surveys and experiments, synthetic microbial communities ( 1 ), and quantitative methods in environmental microbiology and microbial isolation and characterization (e.g., reference 2 ). In addition, we ground our microbiome work in ecological theory and seek to identify and understand the ecological principles that explain overarching patterns across communities and ecosystems (e.g., references 3 and 4 ).…”

“…Our immediate future directions are to determine the composition and structure of the dormant soil microbiome, to understand their resuscitation dynamics given fire, and to quantify the contributions of rare and dormant members to functions. So far, we have evidence that members of the rare biosphere contribute to arsenic resistance ( 2 ) and therefore can have consequences for arsenic transformation in Centralia. We also found that the diverse taxa inhabiting fire-affected soils, on average, have smaller genomes, fewer two-component regulatory systems, and fewer antibiotic resistance and production genes ( 11 ; J. W. Sorensen, T. K. Dunivin, T. C. Tobin, and A.…”