Elevational Gradient Effects on Microbial Distribution in Crude Oil Polluted Sites

Abstract

Crude oil is a major environmental pollutant in the Niger Delta region of Nigeria due to heightened operations of the petroleum industry in this location. This comparative study of two different petroleum hydrocarbon-polluted soils from the Bodo and Tombia communities in Rivers State was carried out to determine microbial abundance (distribution) in relation to the depth and soil texture of the polluted sites. Soil samples were collected at 15 cm and 30 cm from each site. Baseline physicochemical parameters and microbial counts were determined using standard methods. Hydrocarbon utilizing bacteria were screened with 2,6-dichlorophenol indophenol (DCPIP) for crude oil degradation efficiency. The average total petroleum hydrocarbons (TPH) collected from the areas values are higher than the intervention value of 5000 mg/kg as stipulated by the Department of Petroleum Resources (DPR) in the Environmental Guidelines and Standards for the Petroleum Industry in Nigeria (EGASPIN). Microbial distribution patterns were not significantly different (p=0.08) between the topsoil and subsoil in the sites investigated. There was no significant variance in the relationship between soil texture and microorganism distribution (p=0.998). An interaction of the effects between the two independent variables produced an insignificant variance (p=0.411). Average viable culturable heterotrophic and hydrocarbon utilizing microbial counts for the sites varied considerably between 105 and 106 colony forming units per gram of soil (cfu/g) at both depths. A consortium of Pseudomonas spp., Proteus spp., Sphingobacterium spp., and Bacillus spp. isolated from the sites efficiently degraded crude oil, showing a 100% decolourization of DCPIP in Bushnell-Haas-crude oil broth. This study demonstrated that soil texture and depth affect microbial diversity and their function in crude oil contaminated sites.