Occurrence of ars and aox genotypes within as-resistant isolates from the bacterial community of a dismissed industrial area formerly used as a dumping site for roasted arsenopyrite

The present study investigates on the bacterial community structure of arsenic contaminated soil samples from an arsenopyrite dumping site near Scarlino (Tuscany, Italy). 56 different bacterial strains were isolated and phylogenetically identified through 16S rRNA sequencing analysis starting from enrichment cultures in presence of either arsenite As(III) or arsenate As(V) as selective factors. Actinobacteria and Firmicutes resulted to be the main phyla within the As(V) resistant bacteria community, on the other hand Gamma- and Beta-proteobacteria were the prominent classes within the As(III) resistant strains.. The As-resistant isolates were then screened through PCR to assess the occurrence of genes coding for arsenite transporters, arsenate reductases (ars operon), and arsenite oxidases (aox operon). Evidence was gained that 41% of the isolates contained at least a gene related to arsenite transporters, 37.5% a gene related to arsenate reductase, and 23% a gene related to arsenite oxidases. Moreover, two isolates cable of efficiently reducing arsenate were identified. Actually, Deftia acidovorans strain U and Pseudomonas putida strain N showed the ability to reduce 5 mM As(V) within 48h and 72h of incubation respectively. Thus, the bacterial strains here described possess promising traits for a possible exploitation in bioremediation protocols of As polluted environments