Effect of Heavy Metals on β-galactosidase Activity in Marine Bacteria

Background: Due to metal pollution and its toxicity in the coastal areas, the enzymatic activities of bacteria involved in the breakdown of organic compounds are repressed leading to decline in biodegradation rate. Aim: The influence of heavy metals (copper, lead, zinc, manganese and iron) on β-galactosidase activity in three bacterial strains (Providencia stuartii, Pantoea dispersa and Aeromonas dhakensis) isolated from coastal marine sediment collected from coastal zone in Bonny Island, Nigeria was investigated. Methodology: The strains were cultivated in Z- buffered medium having lactose as enzyme inducer. Beta galactosidase assay was done via 2-nitrophenol β-D-galactopyranoside as the substrate. The absorbances of p-nitrophenol solution formed were measured at 420 nm in a spectrophotometer. The β-galactosidase activities were calculated comparative to controls. Results: Presence of the metals significantly affected β-galactosidase activities. Metal concentration of 0.001 mg/L triggered a decrease in enzyme activity. The sensitivity patterns of Pantoea dispersa and Aeromonas dhakensis were Cu>Pb>Zn>Mn>Fe while that of Providencia stuartii was Pb>Cu>Zn>Mn>Fe. The effect of metal stress to enzyme synthesis is reliant on the organism and the metal. This might be described with logistic dose-response model using elevated coefficient of inhibition (R > 0.81). Conclusion: The results revealed that concentration of metal as low as 0.001 mg/L when deposited in the environment has detrimental effect on microbial activities and consequently on biogeochemical cycles. The isolated bacterial strains could serve as ideal organisms for heavy metal toxicity evaluation.