Mitigation of arsenic toxicity in natural waters using a bacterial biomineralizing system

Rivers of the hyper-arid Atacama Desert (Northern Chile), including Loa River, are characterized by extremely variable and harsh conditions, including intense evaporation and high concentrations of heavy metals and toxic metalloids, including arsenic (As). This study evaluated the bioremediation potential of As-resistant urease-producing bacteria isolated from the Loa River sediments to remove As via co-precipitation with calcite in a bioreactor. Preliminary, the bacterial community composition was characterized, using high-throughput Illumina sequencing of the 16 S rRNA genes. The bacterial community was dominated by Proteobacteria (49.09%), (mainly Delta-proteobacteria, Gamma-proteobacteria, and Alpha-proteobacteria), followed by Bacteroidetes (20.18%), and Firmicutes (16.3%). As-resistant bacteria producing urease were isolated. Most isolates (12/16) possessed the arsenate reductase gene and urease activity. Among them, the Shewanella sp. SLO-6 tolerated both arsenite (20 mM) and arsenate (100 mM), successfully removing 82% of total As via co-precipitation with calcite after 120 h incubation in a batch reactor. In addition, after 120 h, a significantly increased the viability (from 38 to 76%) of human umbilical vein endothelial cells; thus, effectively reducing arsenic toxicity. As removing by Shewanella sp. SLO-6 could be proposed as a component of bioreactors in the treatment of arsenic-contaminated waters to concomitantly counteract its harmful effects in aquatic environments.