Bioaccumulation and toxicity of arsenic in cultures of Rivularia halophila, a cyanobacteria isolated from Laguna Negra (Catamarca Argentina)

Abstract

Rivularia halophila (R. halophila) is a filamentous cyanobacteria isolated from microbial mats related to stromatolites formation in Laguna Negra (LN) (Catamarca-Puna-Argentina). The LN is a hypersaline lake rich in heavy metals and metalloids such as arsenic (As). Knowing the potential of R. halophila in the precipitation of calcium carbonates and the possible incorporation of As in the carbonate matrix as an As removal method is the main goal of our study. However, because R halophila has been recently described, a detailed study of its resistance to As enriched environments is needed. Thus, the aim of this study was to evaluate the resistant capacity of R. halophila to high levels of As (as arsenate (AsV) and arsenite (AsIII)). For this aim different biochemical and imaging techniques were performed. The growth (an increase of biomass), the content of chlorophyll a, and the accumulation of As inside the cyanobacteria were assessed. Results indicate that R. halophila has a high As a resistance, especially to AsV. The growth and the chlorophyll-a content were only affected at concentrations higher than 2000 mg∙L-1 for AsV and equal or higher concentration of 10 mg∙L-1 to AsIII. The median lethal dose 50 (LD50) of AsV and AsIII were 8595 mg∙L-1 and 71 mg∙L-1 , respectively. In addition, the accumulation of As within R. halophila increased proportionally with the dose of As in the growth culture medium. The maximum value of As accumulated in the biomass was 70.64 μg∙mg-1 for AsV and 9 μg∙mg-1 for AsIII. Overall, the results obtained from this study indicate that R. halophila is not only a cyanobacteria that is tolerant to high concentrations of As but also has the capability to accumulate substantial amounts of this metalloid inside the sheath and in the cell, making it an excellent model for the study of the removal and resistance of As.