The key role of biogenic arsenic sulfides in the removal of soluble arsenic and propagation of arsenic mineralizing communities

Biogeochemical processes govern the transport and availability of arsenic in sediments. However, little is known about the transition from indigenous communities to cultivable consortia when exposed to high arsenic con-centrations. Such cultivable communities could be exploited for arsenic bioremediation of waste streams and polluted sites. Thus, it is crucial to understand the dynamics and selective pressures that shape the communities during the development of customized bacterial consortia. First, from the arsenic partitioning of two sediments with high arsenic concentrations, we found that up to 55% of arsenic was bioavailable because it was associated with the soluble, carbonate, and ionically exchangeable fractions. Next, we prepared sediment enrichment cultures under arsenate-and sulfate-reducing conditions to precipitate arsenic sulfide biominerals and analyze the communities. The produced biominerals were used as the inoculum to develop bacterial consortia via suc-cessive transfers. Tracking of the 16S rRNA gene in the fresh sediments, sediment enrichments, biogenic min-erals, and bacterial consortia revealed differences in the bacterial communities. Removing the sediment caused a substantial decrease in diversity and shifts toward the dominance of the Firmicutes phylum to the detriment of Proteobacteria. In agreement with the 16S rRNA gene results, the sequencing of the arrA gene confirmed the presence of phylotypes closely related to Desulfosporosinus sp. Y5 (100% similarity), highlighting the pivotal role of this genus in the removal of soluble arsenic. Here, we demonstrated for the first time that besides being important as arsenic sinks, the biogenic arsenic sulfide minerals are reservoirs of arsenic resistant/respiring bacteria and can be used to culture them.

Automated summary

Biogeochemical processes control the transport and availability of arsenic in sediments. Transition from indigenous communities to cultivable consortia exposed to high arsenic concentrations is poorly understood. Understanding the dynamics and selective pressures in the development of bacterial consortia is crucial for arsenic bioremediation. We found that a significant portion of arsenic in sediments is bioavailable and developed bacterial consortia using arsenic sulfide biominerals. Our study highlights the importance of these biogenic minerals as reservoirs of arsenic-resistant bacteria.