Microbial Respiration of Selenium Oxyanions

Selenium oxyanions, selenate and selenite, may be used as terminal electron acceptors during microbial respiration depending on their availability in different environments. Dissimilatory selenate reduction is the process where selenate is sequentially reduced to selenite and further to insoluble elemental selenium used as a terminal electron acceptor for anaerobic respiration. Selenate reduction is major sink for selenium oxyanions in aquatic and soil environments, which can reduce the toxicity when present at high levels, or alternatively immobilize already low levels selenium in deficient regions. Gaining insights into the biogeochemical cycling of selenium in the environment and knowledge of the microbiological and chemical interrelationships is important for improving soil and environmental quality in both selenium-contaminated as well as deficient systems.

We are integrating microbiological, genomic and biogeochemical approaches to study mechanisms of adaptation of selenate-respiring microorganisms in their natural environment. Our data suggests that the process of dissimilatory selenate reduction is ubiquitous and that the organisms carrying out this process exhibit a tremendous species diversity, which has yet to be characterized. There is limited information on the microbiology of respiratory selenate reduction and as of yet only a few selenate-respiring bacterial isolates have been obtained in pure culture and described in greater detail. We have an interesting collection of novel pure cultures capable of selenate and selenite reduction from different soils and sediments and have described new selenate-respiring species, including Sedimenticola selenatireducens and Pelobacter seleniigenes. Our focus is in examining the diversity in speciation, physiology and genes of selenate/selenite respirers from diverse environmental resources. The genome of one of our selenate-respiring isolates is being sequenced by DOE/JGI. The overall goal is to understand the diverse strategies developed throughout evolution for energy production from selenate/selenite respiration and to be able to link the microbial community functionality in anaerobic respiration with the biogeochemical cycling of selenium in the soil environment.