Arsenic Detoxification by Geobacter Species

Insight into the mechanisms for arsenic detoxification byGeobacter species is expected to improve the understanding of global cycling of arsenic in iron-rich subsurface sedimentary environments. Analysis of 14 differentGeobacter genomes showed that all of these species have genes coding for an arsenic detoxification system (ars operon), and several have genes required for arsenic respiration (arr operon) and methylation (arsM ). Genes encoding four arsenic repressor-like proteins were detected in the genome ofG. sulfurreducens ; however, only one (ArsR1) regulated transcription of thears operon. Elimination ofarsR1 from theG. sulfurreducens chromosome resulted in enhanced transcription of genes coding for the arsenic efflux pump (Acr3) and arsenate reductase (ArsC). When the gene coding for Acr3 was deleted, cells were not able to grow in the presence of either the oxidized or reduced form of arsenic, whilearsC deletion mutants could grow in the presence of arsenite but not arsenate. These studies shed light on howGeobacter influences arsenic mobility in anoxic sediments and may help us develop methods to remediate arsenic contamination in the subsurface.IMPORTANCE This study examines arsenic transformation mechanisms utilized byGeobacter , a genus of iron-reducing bacteria that are predominant in many anoxic iron-rich subsurface environments.Geobacter species play a major role in microbially mediated arsenic release from metal hydroxides in the subsurface. This release raises arsenic concentrations in drinking water to levels that are high enough to cause major health problems. Therefore, information obtained from studies ofGeobacter should shed light on arsenic cycling in iron-rich subsurface sedimentary environments, which may help reduce arsenic-associated illnesses. These studies should also help in the development of biosensors that can be used to detect arsenic contaminants in anoxic subsurface environments. We examined 14 differentGeobacter genomes and found that all of these species possess genes coding for an arsenic detoxification system (ars operon), and some also have genes required for arsenic respiration (arr operon) and arsenic methylation (arsM ).