Biodegradation of Chlorpyrifos Insecticide by Bacillus cereus ST06 and Chryseobacterium sp 6024 Isolated from Agricultural Soil, Nigeria

Introduction: Indigenous soil bacteria have the potential to degrade the harmful chlorpyrifos insecticide, this identifies the importance of biodegradation as an eco-friendly method for chemical pollutant cleanup.

Aims: To compare the potential of Bacillus cereus ST06 and Chryseobacterium sp 6024 in biodegrading chlorpyrifos insecticide singly or as a consortium in a liquid medium.

Study Design: Enrichment culture technique was used to evaluate the bacterial potential in biodegrading chlorpyrifos insecticide.

Place and Duration of Study: Agricultural soil sample containing chlorpyrifos degrading bacteria was obtained from Ukukwa village Amansea Nigeria (6o16' 30'' N and 7o 07'30''E) from depths of 15cm. Experiment was conducted from January till March 2022.

Methodology: In this study, previously isolated and characterized Bacillus cereus ST06 and Chryseobacterium sp 6024 by standard microbiological method based on their phenotypic test, biochemical test, cultural morphology and 16S rRNA sequencing was used for the experiment. Their growth response to 20mg/l and 60mg/l chlorpyrifos in mineral salts medium singly and as a consortium was compared and determined by monitoring the optical density at 600nm at the optimum condition of pH 6.5 and 30oC temperature for 28 days. The residual chlorpyrifos concentration after 28 days was also compared and determined using Gas Chromatography- Electron Cathode Detector (GC-ECD).

Results: The result showed a significant difference (P< .001) as Bacillus cereus ST06 and Chryseobacterium sp 6024 responded differently to different concentration of chlorpyrifos. Bacillus cereus ST06 and Chryseobacterium sp 6024 reached maximum growth in medium containing 20mg/l chlorpyrifos with a mean OD of 0.23±0.20 and 0.42±0.02 respectively on 16th day than 60mg/l chlorpyrifos with a mean OD of 0.47±0.02 and 0.81±0.02 respectively on 20th day. The bacterial consortium also reached maximum growth on 20mg/l and 60mg/l of chlorpyrifos with mean OD of 0.21±0.31 and 0.29±0.02 on 20th day respectively. The result of residual chlorpyrifos concentration shows that the bacteria consortium degraded 79 per cent and 78 per cent of 20mg/l and 60mg/l chlorpyrifos respectively, while Bacillus cereus ST06 and Chryseobacterium sp 6024 degraded 63 per cent and 57 per cent of 20mg/l chlorpyrifos and 61 per cent and 37 per cent of 60mg/l chlorpyrifos.

Conclusion: The study shows that bacteria consortium possessed potential to be used in biodegradation of 20mg/l and 60mg/l Chlorpyrifos than the individual isolates. It is therefore recommended that further studies on RNA profiling of each bacterium and synergistic interaction of the bacterial consortium be studied to better understand regulation of genes and individual bacterial roles in degradation chlorpyrifos efficiently.