Herminiimonas arsenicoxydans

Herminiimonas arsenicoxydans strain ULPAs1 (formerly called Caenibacter arsenoxydans ULPAs1, or Cenibacterium arsenoxydans) is an heterotrophic bacterium isolated from the activated sludge of an industrial water treatment plant contaminated with heavy metals such as arsenic, lead, copper, and silver. H. arsenicoxydans is the first fully characterized arsenic-metabolizing microorganism. It is phylogenetically associated with the beta subdivision of the Proteobacteria and belongs to the new genus Herminiimonas comprising bacteria isolated from diverse aquatic environments and anthropized ecosystems. H. arsenicoxydans possesses unsuspected mechanisms for coping with arsenic. Aside from multiple biochemical processes such as arsenic oxidation/reduction, oxidative stress resistance and As[III] extrusion (efflux), H. arsenicoxydans also exhibits positive chemotaxis and motility towards arsenic and metalloid scavenging by exopolysaccharides. These observations demonstrate the existence of a novel strategy to efficiently colonize arsenic-rich environments, which extends beyond oxidoreduction reactions. Genomic and experimental data demonstrated that this organism is capable of accommodating the presence of high concentrations of various toxic metals such as cadmium and zinc. However, except for arsenic, the resistance levels to toxic metals were much lower than those measured in the metallophilic R. metallidurans, which contains multiple plasmid-encoded genes, suggesting a specific physiological adaptation of H. arsenicoxydans toward arsenic. Three clusters of genes involved in resistance to arsenic were identified. Quantitative analysis of the transporter-encoding gene mRNA demonstrated that the resistance operons are either constitutively expressed or induced in the presence of As[III] in H. arsenicoxydans. H. arsenicoxydans can accommodate a wide range of oxygen. Indeed, the H. arsenicoxydans genome harbors multiple respiratory pathways, permitting microorganisms to grow under aerobic, microaerobic, and anoxic conditions. Remarkably, the versatile regulatory system of H. arsenicoxydans enables it to sense dynamic changes in arsenic concentration and to initiate motility and EPS synthesis for attachment to this metalloid. Recent results suggest that microbial biofilms are involved in the adsorption and immobilization of metals (such as Pb[II] and Cr[III]). The ability of H. arsenicoxydans to scavenge arsenic in an EPS matrix may be of prime importance in the context of bioremediation of contaminated environments, leading to the sequestration of this toxic metalloid. (EBI Integr8)