Growth Optimization of Glyphosate-based Herbicides Utilizing Bacteria isolated from Lotic Water of Ogini Stream, Nigeria

Glyphosate-based herbicides are often used for the control of weeds grown on agricultural fields or farms. Different health problems have been reported to be associated with the use of glyphosate-based herbicides mainly due to their toxicity level. Thus, finding glyphosate utilizing microorganisms to remediate the glyphosate-based herbicides in the environment is crucial. The culture conditions for maximum utilization of glyphosate by bacterial isolates, Stenotrophomonas maltophilia, Bacillus cereus and Enterobacter aerogenes previously isolated from Ugini stream close to corn fields treated with glyphosate-based herbicide at Ofagbe, Delta State, Nigeria were optimized using mineral salt medium containing glyphosate as carbon source. The varied culture parameters assessed were temperature (30, 37 and 40 oC), pH (5, 6, 7, 8 and 9), initial glyphosate concentration (1, 3, 5, 7 and 9 g/L) and incubation time (2-14 days). Optical density (OD) at 560 nm of the culture was used to estimate cell growth or cell load of the glyphosate utilizing bacteria strains at every 2 days for 14 days. The following optimal conditions were determined: initial pH 9.0, incubation temperature 30 °C, initial concentration of glyphosate (1g/L) and incubation time of 12 days. Of the isolates on the medium containing the herbicide as sole carbon and energy source, Bacillus cereus showed the highest growth level (OD average, 0.127, pH average, 6.26. This was followed by Stenotrophomonas maltophilia (OD average = 0.114, pH average = 6.44) and Enterobacter aerogenes (OD average = 0.100, pH average, 6.56). At the increased of glyphosate in the medium there was decreased in growth of the bacteria. Bacillus cereus, Stenotrophomonas maltophilia and Enterobacter aerogenes indicated a high capacity to be able to degrade glyphosate. It is therefore concluded that the bacteria employed in this research can be recommended for bioremediation of environments contaminated with this chemical and further research should conducted to ascertain the catabolic genes present in these individual glyphosate degrading bacteria.