Growth Patterns and Degradative Potentials of Pseudomonas sp. Isolated from Waste Dumpsite Soil in Crude Oil Supplemented Soil Extract and Mineral Salts Media

Introduction: Pollution caused by crude oil and its products is the most prevalent and widespread problem in soil and water environments and is increasingly being implicated as being responsible for the global warming menace being battled worldwide

Aims: This study was carried out to evaluate the potential of Pseudomonas sp. from dumpsite soil to degrade crude oil hydrocarbons.

Place and Duration of Study: Department of Microbiology, Ekiti State University, Ado Ekiti, Nigeria, October 2013-May 2015.

Methodology: Soil samples from different locations of Ekiti State Waste Management Board dumpsite in Ilasa, Ado-Ekiti were collected and screened for crude oil utilizing Pseudomonas sp. the isolates were screened using vapour transfer method and the growth kinetics of the selected best degrading species were monitored in mineral salt and soil extract media by measuring optical density. The rate of degradation was evaluated via gas chromatography and mass spectroscopy analysis. The effects of heavy metals on degradation was also evaluated as well as the presence of plasmids in the degrading species.

Results: Eighteen Pseudomonas spp. isolated from municipal waste dumpsite soil were recovered using standard microbiological methods. Five species Pseudomonas OWPSA. OWPS11, OWPS6, OWPS5 and OWPSJ showed enhanced ability to utilize crude oil hydrocarbons at concentrations up to 2.5% v/v with optimal utilization at 2.0%. All the Pseudomonas spp. showed tolerance to zinc and lead but were less tolerant to cobalt and mercury. The Gas Chromatography and Mass Spectroscopy analyses of the residual crude oil from the treatments revealed that Pseudomonas sp. OWPSJ exhibited the highest degradation efficiency in soil extract media resulting in loss of 18 peaks. There was marked reduction of hydrocarbon fractions by 75- 90% while the naphthalene fraction of the oil inoculated with Pseudomonas sp. OWPS11 increased. However, Pseudomonas sp. OWPS6 exhibited degradation of hydrocarbons fractions than strain Pseudomonas sp. OWPS11 with loss of 16 peaks. Plasmids were not observed to occur hence suggesting the possibility of the genes being located on the chromosome. Residual components of degradation were esters, methylated benzenes, alcohols and organic acids as well as shorter chain alkanes.

Conclusion: This study establishes the prospect of soil extract media as alternative media for evaluating the degradative ability of bacteria and also the potential of strain Pseudomonas sp. OWPSJ, isolated from a non-petroleum contaminated site as a good bioremediation agent for crude oil spills.