Assessing the potential of Rivularia halophila for arsenic removal

Abstract

Rivularia halophila (R. halophila) is a filamentous cyanobacteria isolated from microbial mats of the Laguna Negra Lake (LN), Catamarca, Puna-Argentina. The LN is a high-altitude hypersaline lake, where extreme environmental conditions (i.e., high UV-radiation and extreme temperature, salinity, and water activity) restrict eukaryotic life. Besides, the presence of arsenic (As) has been detected in water, sediments and lithified microbial mats. This particular cyanobacteria is part of a microbial consortium that participates actively in the carbonate precipitation process. Taking this into account, the objective of this study were (i) to evaluate the capability of R. halophila to tolerate moderate to high As concentration and (ii) to assess the role of this cyanobacteria in carbonate precipitation with the potential incorporation of As in the carbonate lattice. Tolerance and resistance experiments were perform under different As (III and V) concentration, and evaluated by biomass growth, pigment intensity and chlorophyll a content. Besides, lethal dose 50 (LD 50) was also evaluated. On the other hand, carbonate precipitation experiments were perform under different calcium concentrations and moderate levels of As (similar to LN concentrations). Optical and electronic microscopy images of the precipitates were taken and measured near the cyanobacterial sheaths and from the bottom of the culture flask. DRX analysis were also performed. Preliminary results showed that R. halophila tolerates high concentrations of As (III and V), especially As (V), and can accumulate As in the sheath and in the cells. Moreover, R. halophila might facilitate carbonate precipitation in culture. The precipitation of amorphous crystals, near the sheath, were observed with the addition of As (V); while without R. halophila the minerals were mostly geometric, corresponding to chemical precipitation. All the results obtained until now, give us some clues about the potential of this cyanobacteria for As bio-removal.