A Tale of Two Oxidation States: Bacterial Colonization of Arsenic-Rich Environments

Microbial biotransformations have a major impact on contamination by toxic elements, which threatens public health in developing and industrial countries. Finding a means of preserving natural environments—including ground and surface waters—from arsenic constitutes a major challenge facing modern society. Although this metalloid is ubiquitous on Earth, thus far no bacterium thriving in arsenic-contaminated environments has been fully characterized. In-depth exploration of the genome of the β-proteobacterium Herminiimonas arsenicoxydans with regard to physiology, genetics, and proteomics, revealed that it possesses heretofore unsuspected mechanisms for coping with arsenic. Aside from multiple biochemical processes such as arsenic oxidation, reduction, and 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. Such a microbial mechanism of detoxification, which is possibly exploitable for bioremediation applications of contaminated sites, may have played a crucial role in the occupation of ancient ecological niches on earth

Arsenic oxidation of Cenibacterium arsenoxidans : Potential application in bioremediation of arsenic contaminated water

Arsenic is a naturally occurring metalloid present in many organic and inorganic compounds. The most abundant arsenic species are the inorganic As[III] and As[V]. The prolonged exposure (occupational or natural) of humans to nonlethal arsenic doses causes chronic health effects, but in long time period usually causes death. Therefore, different chemical technologies were developed for arsenic decontamination of water. Most of them have two stages – the oxidation of As[III] into As[V] and the subsequent immobilization of As[V]. The main disadvantage of these technologies is the use of strong chemical oxidants, which causes a secondary pollution of the environment. The replacement of the chemical oxidation step by a biological one has potential for development, mainly due to the lack of secondary pollution and the low impact on the environment. We focused our interest on the studies of an arsenic-oxidizing β-Proteobacterium, recently named Cenibacterium arsenoxidans, which possess high arsenic –oxidation capacity. These studies are the preliminary step in order to develop a microbial oxidation step for an arsenic contaminated water cleanup technology. We investigated the optimal growth conditions of the strain, and new nutrient media were tested and developed. In addition to the studies of the As[III] oxidation from free cells, the As[III] oxidation from immobilized C. arsenoxidans cells were studied. Thereafter, a tracking of the growth of C. arsenoxidans gfp-tagged cells in an “open” system was performed, which aimed to clarify the colonization and survival ability of the strain in such system, where randomly introduced microorganisms were presented. Also a method for rapid screening of arsenic-transforming bacteria was developed. L’arsenic est un métalloïde naturellement présent dans différents environnements. Les formes inorganiques, l’arsénite (As[III]) et l’arséniate (As[V]) sont les plus abondantes. Ce sont aussi les formes les plus toxiques. L’ingestion d’arsenic, en particulier via l’absorption d’eau contaminée, est à l’origine de graves problèmes de santé publique dans des nombreuses parties du monde. C’est pourquoi, différentes méthodes de bio-réhabilitation ont été mises au point. La plupart de ces méthodes utilisent deux étapes : une oxydation chimique de As[III] en As[V], suivie de l’immobilisation de l’As[V]. L’utilisation d’oxydants puissants est à l’origine de pollutions secondaires. L’oxydation par voie microbiologique de l’As[III] permet de proposer une méthode alternative intéressante puisque non polluante. Notre travail s’est focalisé sur l’analyse d’une β-protéobactérie, Cenibacterium arsenoxidans, capable d’oxyder efficacement l’As[III] en As[V]. Nos études constituent des étapes préliminaires pour le développement de méthodologies destinées au traitement d’eaux contaminées par l’arsenic. Nous avons établi les conditions d’obtention de la biomasse d’intérêt en testant de nouveaux supports de culture, basé sur la valorisation de déchets d’industries agroalimentaires. L’oxydation d’As[III] par C. arsenoxidans a été testée avec des cellules en suspension ainsi qu’avec des cellules immobilisées dans des billes d’alginate. En utilisant des cellules marquées avec la protéine GFP, nous avons étudié la survie et l’implantation de C. arsenoxidans en milieu non stérile. Enfin, dans le but d’isoler d’autres bactéries utilisables dans les processus de traitements de milieux contaminés par l’arsenic, nous avons développé une méthode simple et rapide pour le criblage de bactéries capables de réaliser l’oxydation d’As[III]

Life based on phosphite: a genome-guided analysis of Desulfotignum phosphitoxidans

The Delta-Proteobacterium Desulfotignum phosphitoxidans is a type strain of the genus Desulfotignum, which comprises to date only three species together with D. balticum and D. toluenicum. D. phosphitoxidans oxidizes phosphite to phosphate as its only source of electrons, with either sulfate or CO2 as electron acceptor to gain its metabolic energy, which is of exclusive interest. Sequencing of the genome of this bacterium was undertaken to elucidate the genomic basis of this so far unique type of energy metabolism