The role of dissimilatory arsenate reducing bacteria in the biogeochemical cycle of arsenic based on the physiological and functional analysis of Aeromonas sp. O23A.

Dissimilatory arsenate reducing bacteria (DARB) are known to contribute to the mobilization of arsenic and other elements from minerals. Despite this, metabolic capabilities of only a few DARB strains have been thoroughly investigated so far, and the influence of these bacteria on the bioavailability of arsenic in the environment is still a topic for discussion. In this study, Aeromonas sp. O23A, one of the dominant DARB strains found in the Zloty Stok mine (SW Poland), was subjected to a detailed physiological and functional analysis aimed to identify the actual environmental impact of this strain. Physiological analyses revealed that O23A is a facultative anaerobe, capable of utilizing arsenate as a respiratory substrate and acetate, citrate and lactate as electron donors. Arsenate reduction was observed within the first 24h of culturing. The strain shows high resistance to arsenic and several other heavy metals (i.a. Cu, Fe, Ni and Zn) as well tolerance to a broad range of physico-chemical conditions. Metabolic preferences of O23A were thoroughly investigated using Biolog™ MicroArray assay. The strain was found to produce hydroxamate siderophores, potentially involved in the mobilization of iron and co-occurring heavy metals from minerals. On the other hand, O23A showed high adherence abilities, and its involvement in biofilm formation may lead to the entrapment of dissolved arsenic species and other toxic ions. The results shed light on the importance of arsenic respiration and resistance in the overall metabolism of Aeromonas sp. O23A and confirmed its key role in the biogeochemical cycle of arsenic, also in the context of self-purification of heavy-metal-contaminated waters.