Abstract Description

Indigenous bacteria sourced from metal-rich environments possess mechanisms which allow bio-precipitation. Bacterial bio-precipitation is achieved by aiding the formation of insoluble metal complexes through stimulating redox processes, leading to the reduction of their bioavailability and toxicity. This study aimed to elucidate the cellular processes involved in the bacterial bio-precipitation of heavy metals utilizing bacterial isolates obtained from mine wastewater effluents. Chemical analysis was determined by hand-held probes in the laboratory, and the concentrations of elemental metal compositions were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Water samples were used as inocula on selective media composed of nutrient agar and heavy metals as selective pressure. Growth factors such as oxygen availability and pH values (5, 7 and 9) were assessed to determine their effects on the growth and interaction of metals and bacteria. The minimum inhibitory concentration (MIC) and maximum tolerance concentrations (MTC) of the bacterial isolates were analyzed using different metal concentrations of Vanadium (V3+), Zinc (Zn2+) and Lead (Pb2+) as key heavy metals detected in the wastewater samples. Bacterial isolates tolerating the highest inhibitory concentration were selected to analyze the different strategies of metal bio-precipitation using scanning electron microscope (SEM) and the transmission electron microscope (TEM). Chemical analysis of the samples from Site 1, Site 2 and Site 3 revealed sulfate (SO42-) concentrations of 2568, 6115 and 2720 mg/L, respectively, with various metal (V5+, Zn 2+, Cu2+ and Fe3+) concentrations at levels surpassing South African National Standards (SANS) limits. A total of 19 aerobic and 15 anaerobic bacterial isolated were obtained. From the total isolates obtained, 32 (94%) were able to tolerate 500 mg/l of V3+, while 16 (47%) tolerated up to 500 mg/L of Pb2+, and 18 (52%) tolerated up to 1400 mg/L of Zn2+. SEM and TEM analysis revealed biosorption, and bioaccumulation of the precipitated metals. These results revealed that indigenous isolates have different mechanisms of precipitating different metals, aiding our understanding of metal-microbe interactions.