The Effect of Atrazine On Microbial Population and Diversity In Marine Coastal Surface Water
The effect of atrazine on aerobic culturable microbial population and diversity in coastal surface water collected from Bonny Island in the Niger Delta was investigated in the laboratory. Plastic bowls were used to set-up microcosms of coastal surface water sample to simulate various atrazine contaminations. The water sample (2.0 L) was put into each of the bowls and treated at 50, 100, 150, 200, 250 mg/l of the herbicide active ingredient. The untreated water sample (2.0 L) kept also in a plastic bowl served as control. Microbial enumeration and isolation of aerobic heterotrophic bacteria, filamentous fungi and yeasts in the treated and untreated water were carried out every 2 days for 10 days using spread plate method. Reduction in number of microorganisms was observed with increase in herbicide concentration. The microbial population for all treatments reduced at the 2nd, 4th and 6th day of post treatment but increased progressively at the 8th and 10th day. The microbial generic diversity also decreased with atrazine treatment. A total of 18 bacterial and 18 fungal isolates were identified from the untreated (control) seawater. Bacteria of the genera Bacillus, Pseudomonas, Aeromonas, Vibrio, Lactobacillus, Flavobacterium, Micrococcus, Escherichia, Acinetobacter, Enterobacter and Staphylococcus were isolated at different frequencies with Bacillus predominating. Fungi of the genera Aspergillus, Fusarium, Penicillium, Rhizopus, Cladosporium, Saccharomyces, Candida, Cryptococcus and Debaryomyces were isolated at different frequencies with Aspergillus and Saccharomyces predominating. The microbial genera isolated from the herbicide treated seawater were mainly Bacillus, Pseudomonas, Acinetobacter, Aspergillus, Fusarium, Saccharomyces and Candida. These resistant microorganisms can be exploited for bioremediation of atrazine contaminated environment. The suppression of some microbial strains is an indication that herbicides from terrestrial run-off can influence the composition of the microbial community and have a critical impact on the overall functioning of the marine ecosystem.