Evaluating pH and Temperature Effects on Heavy Metal Removal by Soil Bacteria

Abstract

Microbial removal of heavy metals is indicated to be effective and eco-friendly. However, since microorganisms possess varying ranges for their biochemical activities and removal capabilities, establishing optimum pH and temperature conditions are essential in the removal of heavy metals. Therefore, this study was aimed at determining the effects of pH and temperature on nickel, lead and cadmium tolerance by ten soil bacterial strains. The bacterial strains were isolated from soils within Afe Babalola University, Nigeria, using the standard pour plating method. Identification of the isolates was carried out using polymerase chain reaction and gene sequencing methods. Sequences were deposited in the National Centre for Biotechnological Information database and accession numbers were obtained accordingly. The study was carried out in batch experimental setups. Media pHs of 5, 7 and 9 and incubation temperatures of 30, 35 and 40 oC were used for the study. At the different pH, significant highest nickel tolerance was observed at pH 5 in presence of most of the bacterial strains. Generally, tolerance index to lead in presence of the bacterial strains ranged between 0.28 and 5.0. At the respective incubation temperatures, significant highest tolerance to nickel was observed at 30 ⁰C in the presence of Enterobacter cloacae (OQ383316), Bacillus cereus (OQ383317), Alcaligenes faecalis (OQ383318), Alcaligenes faecalis (OQ383319) and Bacillus subtilis (OQ383320) and at 40 ⁰C in the presence of Yersinia enterocolitica (OQ383311), Alcaligenes faecalis (OQ383312), Bacillus cereus (OQ383313) and Bacillus subtilis (OQ383315). Tolerance index of the bacterial strains to lead showed significantly highest value at incubation temperature of 35 ⁰C in presence of most of the test bacterial strains. Lead removal was however observed to be significantly highest at 40 oC. In the case of cadmium, significantly highest tolerance index and removal were observed at 30 ⁰C and 40 ⁰C, respectively. The study revealed that pH and temperature conditions could greatly affect the extent of tolerance and removal by the test bacterial strains.