Author: Nwankwo Innocent Chidimma
Department: Applied Microbiology
Affiliation: Nnamdi Azikiwe University Awka

Forty one bacterial isolates which were obtained from a designated area, were screened for their ability to utilize the herbicides glyphosate and paraquat as sole carbon source using standard microbial techniques. Only three bacterial isolates were able to utilize glyphosate and paraquat as their sole source of carbon. These bacterial isolates were Bacillus cereus, Serratiamarcescens and Staphylococcus sciuri. The results for screening test for herbicide utilization measured at 345nm after 2weeks for paraquat and glyphosate in mineral salt medium were 0.438/0.619, 0.272/0.410, and 0.239/0.340 for Bacillus cereus, Serratiamarcescens and Staphylococcus sciuri respectively. The screening test with mineral salt herbicide medium revealed that Bacillus cereus showed the highest utilization ability while the least was shown by Staphylococcus sciuri. All the bacterial isolates grew at alkaline pH after 20days biodegradation. Statistical analyses using ANOVA, T-test and Correlational Matrix were also determined. Comparing paraquat and glyphosate, there is significant difference between the two at P>0.05. The t-test results for insitu and exsitu residue content revealed that paraquat had higher residue content exsitu 0.575 than insitu 0.376 and glyphosate had higher residue content of 0.572exsitu than insitu 0.333. Degradation of glyphosate and paraquatby the single culture and mixed culture were also confirmed using Gas Chromatography. For paraquat, the results showed that the mixed culture had the highest ability (62.77%) to degrade it, followed by Bacillus cereus (57.57%), then Serratiamarcescens (56.58%) lastly Staphylococcus sciuri(37.78%). For glyphosate, the result showed that Bacillus cereus had the highest ability (100%) to degrade it followed by Serratiamarcescens (50.24%), Staphylococcus sciuri (48.89%) and lastly mixed culture (34.67%). Since all these isolates are beneficial to the development of soil, the result showed that when the right dilution is made before the spray of the herbicides, the microorganisms will use these herbicides as a source of carbon thereby degrading these herbicides which will make it less toxic to these microorganisms and humans, but if the concentration is too high, adverse effect ensues.

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