The novel arsenic resistance genes of Bacillus sp. CDB3

Despite its naturally low abundance, the presence of arsenic is near ubiquitous in the environment, attributable to geological and anthropogenic sources. It is not surprising that all organisms have evolved detoxifying mechanisms to deal with intracellular arsenic, with many of the basic detoxification systems are conserved across phyla. The most common and best characterised mechanism amongst microorganisms is the efflux of arsenic from the cytosol by either sequestration or extrusion. In this system, pentavalent arsenate is reduced to trivalent arsenite that is then removed from the cytosol via a transporter or ATP-driven pump. In bacteria, the genes that encode the resistance determinants responsible for this system are organised into arsenic resistance (ars) operons, which can be found in the chromosomes and plasmids of all major bacterial phyla. The fundamental ars gene system consists of a regulatory repressor (arsR), a chemiosmotic arsenite specific transmembrane transporter (arsB/arsY), and an arsenate reductase (arsC). Many bacterial ars operons also see the addition of further genes, the two most common of which are arsD; a secondary regulator and metallochaperone, and arsA, an oxyanion stimulated ATPase that serves to couple arsenite extrusion with ATP hydrolysis. However, these are by no means the only additional ars genes observed, with many novel ars genes being identified. Bacillus sp. CDB3, a strain isolated from an arsenic-contaminated cattle dip site in Northern NSW, Australia, possesses two ars operons – the largest of which exhibits both a novel arrangement of ars genes and two orfs; orf7 and orf8, which encode proteins previously unimplicated in arsenic resistance. This thesis presents the putative identification of the protein encoded by orf8 as a dual-specificity protein phosphatase, and the biochemical characterisation of its activities as both a phosphatase, and a novel arsenate reductase.