Microbes from wastewater treated mangrove soil and their heavy metal accumulation and Zn solubilization

The present study isolated and identified six species of bacteria and fungi from the rhizosphere soil of mangroves species (Avicennia marina), treated for 60 days with artificial wastewater, and further tested for their potential in heavy metal accumulation and Zn solubilization. The wastewater treated mangrove soil had higher microbial counts, porewater salinity and nutrients (N, P, K, total organic carbon), but lower soil bulk density, pH and temperature. The predominant bacterial strains isolated from the treated soil were identified as Bacillus altitudinis, B. anthracis and B.marisflavi, and the fungal strains as Penicillium citrinum, Aspergillus quadrilineatus and Gibberella intermedia. The heavy metal accumulation was determined in those microbial strains cultured with artificial wastewater under shaker culture for seven days. The accumulation was the highest for Zn (70% over control), Cu (62%), Pb (62%) in the bacterium, B. marisflavi and for Mn (50%) in the fungus, P. citrinum. The B. marisflavi was further tested for Zn solublization in terms of pH decline, after 10 days of incubation with the insoluble Zn sources (ZnO, ZnSO4 and ZnCO3). The highest activity of 31.6% pH drop was observed with ZnO. Overall results revealed the potential of B. marisflavi in heavy metal removal and Zn solubilization.