Monitoring the Bio-Utilization of Herbicide (Paraquat Dichloride) by Some Bacterial Species Isolated from Soil in Calabar, Cross-River State, Nigeria

Herbicides though capable of killing weeds, also affect soil microorganisms depending on the dosage applied. They can also be used as sources of food for energy and growth by microorganisms. Some herbicides persist in the soil for a long period of time. These groups can be degraded by soil microorganisms. Thus this research was aimed at examining and isolating soil bacteria capable of utilizing the herbicide (paraquat dichloride), applied at different concentrations on the plot and also to assess its effects on the bacterial isolates. Using nutrient agar medium incorporated with nystatin to inhibit the growth of fungi, bacteria such as Bacillus sp., Micrococcus sp., Klebsiella sp., Pseudomonas sp., Listeria sp., Proteus sp., Streptococcus sp., and Staphylococcus sp were isolated. Screening test with mineral salt medium showed that all the isolates were able to utilize paraquat as substrate for growth and energy. The study also showed that Micrococcus sp., Bacillus and Proteus species especially were able to degrade the herbicide. Bacillus persisted till the eight weeks and was the most frequently isolated, followed by Micrococcus and Proteus sp. An increase was observed in microbial count within the first four weeks (5 *10 8 to 5.34 *108 and 5.3 *10 8 to 6. 64 *10 8 for plots 1 and 3 respectively) but by the sixth week the count decreased (4.70 * 108, 6.38 *108 for plots 1 and 3 respectively) as a result of substrate utilization simultaneously with degradation.