Isolation and identification of an acid-tolerant microalgae and its physiological response to manganese ion stress

Abstract:

[Objective] The purpose of this study was to investigate the growth characteristics of Graesiella sp. and the influence of pH and Mn²⁺ in acidic manganese-containing extreme water environments. [Methods] The purified algae was isolated from an acid mine drainage in a pyrite mine and identified by morphological observation and 18S rRNA gene sequencing. Firstly, we investigated the effects of pH and typical metal ion Mn²⁺ concentration on its growth characteristics. Then, with the determination of algae biomass, photosynthetic pigment, malondialdehyde (MDA), reduced glutathione (GSH) content and the specific vitalities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), we analyzed the physiological response mechanism of the algae to Mn²⁺ stress.[Results] The isolated algae strain was identified and named as Graesiella sp. MA1. The medium pH had a significant effect on the growth of Graesiella sp. MA1, and its minimum initial tolerance pH was 3.5. When the initial pH was 3.5 and the concentration of Mn²⁺ was 5, 30 and 55 mg/L, the biomass of algal decreased with the increase of Mn²⁺ concentration. The Mn²⁺ concentration in experimental groups also decreased by 28.62%, 21.90% and 18.84%, respectively, and the pH value increased to 5.7, 5.6 and 5.4, respectively, while the pH value in control group was 9.1. After 24 days, the chlorophyll a/b value of algal decreased with the increase of Mn²⁺ concentration, while the contents of MDA and GSH, and the specific activities of SOD and APX increased significantly. The results showed that Graesiella sp. isolated and purified from acidic mine drainage could tolerate both low pH and Mn²⁺ in a certain concentration range. Under such extreme environment, the intracellular antioxidant system of Graesiella sp. could reduce membrane lipid peroxidation, and thus play an important role in tolerance of heavy metal ions and detoxification. [Conclusion] Graesiella sp. MA1 can tolerate low pH and heavy metal ions and generate alkalinity, thus this study provides a theoretical basis for in situ bioremediation of acidic mine drainage by using Graesiella sp..