Utilization of Petroleum Hydrocarbon Invitro by Rhizosphere Bacterial Isolates of Groundnut (Arachis hypogeae)

The continuous increase in the use of petroleum hydrocarbon (PHC) worldwide due to industrial revolution has led to severe contamination of our terrestrial and aquatic environment. This has affected our ecosystem and human health negatively. Nigeria, one of the major PHC producing nations in the world is also facing the problem of large numbers and size of areas contaminated with PHC arising from accidental or deliberate spills and leakages such as intentional or accidental bursting of pipelines. Estimated cost for cleanup of contaminated sites using conventional techniques is enormous, insufficient and may not even be contemplated by a developing nation like Nigeria which is facing other serious economic challenges of long time infrastructural neglect that is requiring urgent attention to avoid collapse. Consequently alternative biological techniques have continued to emerge around the world like the process of using rhizosphere bacterial isolates of groundnut being described in this research. Rhizosphere soil bacterial isolates of groundnut variety RMP91 was sampled for their ability to utilize PHC. They were also analyzed for their ability to utilize PHC as carbon and nitrogen source. A total of 6 bacterial isolates were identified from the rhizosphere soil of groundnut to be capable of utilizing PHC namely: Pseudomonas aeruginosa, Pseudomonas fluorescens, Bacillus cereus, Bacillus subtilis, Proteus vulgaris and Klebsiella pneumoniae. The analysis was carried out using mineral assay medium supplemented with the PHC and measurement of optical density of the cultures at 540nm. Higher growth profile rate was observed for mixed culture which was significantly higher than when the isolates are in monoculture at (p < 0.05). The growth profile pattern of mixed culture exhibited is an inverse proportionality with the pH profile. Ps. aeruginosa showed higher growth profile rate among the monoculture with lower profile observed for Ps. fluorescens, B. subtilis, B. cereus, and P. vulgaris respectively. K. pneumoniae as monoculture was not able to utilize the various concentrations of the PHC but do in mixed culture. Only Ps. aeruginosa and Ps. fluorescens were able to utilize PHC as carbon and nitrogen source, while B. subtilis and B. cereus were able to do so as carbon source only. P. vulgaris and K. pneumoniae were not able to utilize PHC as either carbon or nitrogen source. The result therefore suggests that some of the isolates could serve as seed for bio-augmentation during rehabilitation of PHC polluted soil environment.