The effect of glucose and nitrogen supplementation on cell metabolic activity and the reduction of selenite to elemental selenium by Pseudomonas stutzeri NT-I

Abstract

Selenite (Se(IV)) readily bio-accumulates as compared to elemental selenium (Se(0)) which is considered to be biologically inert and relatively less toxic, therefore its microbial reduction from selenium laden waters is imperative. This study investigated the effect of glucose (carbon source), NH4Cl (nitrogen source) and the metabolic activity on the reduction of 2 mM Se(IV) by Pseudomonas stutzeri NT-I in order to establish the mechanism employed the bacterium. The experiments were performed aerobically under previously determined optimum conditions. Four batches were compared. These were A) glucose (10 g.L-1) and ammonium chloride (1.604 g.L−1), B) glucose only (10 g.L-1), C) no added glucose or nitrogen, and D) 1 M of the metabolic inhibitor, sodium azide (NaN3). The highest average biomass-based selenite reduction rate of 0.1061 mmol.(g.h) −1 was in the presence of glucose and nitrogen as compared to 0.0638 mmol.(g.h)−1 in the presence of glucose alone. The reduction rate decreased in the batches which did not have either of the nutrients. The lowest average biomass-based reduction rate of 0.026 mmol.(g.h)-1 was measured for the batch which had the NaN3. The overall Se(IV) removal followed a similar trend to the one observed with reduction rate, with highest reduction of 90.83 % recorded in the first batch and the lowest of 35.68 % being in the presence of NaN3.