Abstract
Biodegradation of crude oil-polluted soils by bacterial isolates was carried out experimentally, to determine the ability of bacterial isolate to utilize and detoxify crude oil-polluted soils. Three soil samples were collected from crude oil-polluted sites of Owazangboko, Abia State, Aguleri-otu, Anambra State and Obi-igbo, Rivers State, Nigeria. Microbiological analysis and physico-chemical analysis were carried out in the Microbiology Laboratory of Chukwuemeka Odumegwu Ojukwu University, Uli. Physico-chemical analysis was carried out to determine the pH, moisture content, water holding capacity and total organic carbon of the soil samples. Microbiological analysis was carried out using serial dilution and spread plate methods to determine the total viable count, enumeration of hydrocarbon utilizing bacteria (HUB) was done using vapour phase method on mineral salt agar monitored at the wavelength of 600nm for 5 days. Adaptation test was carried out and monitored for 5 days using mineral salt broth containing 1ml and 2ml of sterile crude oil separately. A consortium of six effective isolates was taken for the biodegradation of the crude oil, which was monitored for 14 days. Biochemical tests were carried out on the isolates. Polymerase chain reaction (PCR) technique was used to confirm the identity of the isolates. Gas chromatographic flame ionization detector (GC-FID) was used to monitor the amount of the residual total petroleum hydrocarbon after the biodegradation study. Results of physic-chemical analysis showed; pH value of 3.7– 6.6, moisture content 1.6 – 4.4., water holding capacity 28.0 – 32.0., total organic carbon 3.4 – 7.1. Results of total viable count were in the range of 7.1×106 - 5.9×1010. Results of vapour phase method ranged from 0.16 – 0.66. Adaptability test revealed values, 0.11 – 0.54. Biochemical test results revealed Bacillus spp., Pseudomonas spp., Serratia spp., Micrococcus spp., Arthrobacter spp., Proteus spp., Shigella spp. PCR results gave the identity of the organisms to be Lysinibacillus spp. M2c, Serratia marcescens Mb4, Bacillus aerius TPM-23, Proteus mirabilis LS-3 and a new unidentified bacterium. TPH concentrations were in the range of 582.67 mg/l – 123.67 mg/l for Lysinibacillus spp. M2c and Serratia marcescens Mb4, 682.65 – 203.85 mg/l for Bacillus aerius TPM-23and 753.32 mg/l – 324.77 mg/l for Proteus mirabilis LS-3 and the new unidentified bacterium. The effect of bacterial growth across the days showed a p-value of 0.000 less than the α-value 0.01, this concluded that the growth of the bacteria across the days was significant for both vapour phase test and adaptability test. From this study it is evident that Serratia marcescens Mb4 and Lysinibacillus spp. M2c could be used to effectively treat crude oil-polluted environment.
Highlights
Crude oil pollution has been considered a global concern to both humans and the environment
The physico-chemical analysis of the contaminated soil sample showing the percentage of total organic matter, pH, moisture content, water holding capacity of the crude oil soil samples are presented in Table 1: below
Table: 2 showed that the bacterial load was high for all samples, this may be because the crude oil contaminated soil favored the growth of the organisms present in the soil sample, similar results were seen in the research conducted by Omotayo et al [27]
Summary
Crude oil pollution has been considered a global concern to both humans and the environment. In Nigeria, there is an average of 300 oil spills every year [1]. Environmentalists consider the Niger Delta region of the country as one of the world’s most polluted regions [35]. The Niger Delta region consists entirely of nine States which include Abia, Akwa Ibom, Bayelsa, Cross Rivers, Delta, Edo, Imo, Ondo and Frontiers in Environmental Microbiology 2019; 5(1): 14-28. The Niger Delta region, the base of the Nigerian oil and gas industry, generates over 90 percent of the nation’s foreign exchange earnings. In spite of the increasing revenue from crude oil exploitation, the communities from which this resource flows in the Niger Delta continue to live in conditions of social deprivation and abject poverty
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