Effect of Crude Oil Contamination on Microbial Community Structure and Urease Activity in Coastal Plain Sands of Uyo, Akwa Ibom State, Nigeria

Abstract

Petroleum pollution of soils is a major environmental problem. Soil microorganisms can decompose a significant fraction of petroleum hydrocarbons in soils. This research was conducted to investigate the effect of crude oil contamination on microbial community structure and Urease activity. This experiment was conducted from 2020 to 2021 at the Department of Soil Science and Land Resources Management, University of Uyo. The experiment was a pot experiment. Garden soil weighing 1.6kg was placed into five different plastic pots and the following quantities of crude oil dispensed into them: 0 (control), 4. 8, 16 and 24 ml representing 0, 0.25, 0.5, 1.0 and 1.5 percent pollution levels. This was repeated in triplicates giving a total of 15 pots and placed in a screen house. Soil samples were collected from each pot on the 2, 4, 6 and 8 weeks after contamination (WAC). Soil samples were analyzed for bacterial, fungal and population, and urease activity. The results revealed that bacterial cell density decreased by one log order of magnitude from 2.67 x 107 cfu/g to 9.13 x 106 cfu/g soil in week 8. At 0.25 percent population level bacterial cell decreased from 2.38 x 107 in (week 2) to 4.02 x 106 cfu/g soil (week 8). At 0.5 percent pollution level, bacterial cell density decreased from 2.37 x 107 (week 2) to 1.46 x 107 cfu/g soil (week 8). At 1.0 percent pollution level bacterial cell density decreased from 2.30 x 107 (week 2) to 9.56 x 106 cfu/g soil (week 8) and at 1.50 percent pollution level bacterial cell density decreased from 2.21 x 107 (week 2) to 1.22 x 107 cfu/g soil (week 4), and there after rose to 3.16 x 107 (week 6) and then decreased to 8.0 x 106 cfu/g soil (week 8). A total of 16 bacterial genera were identified the most abundance was Bacillus subtilis (23.53%) followed by Micrococcus albus (18.83%), and Bacillus cereus. Unlike bacteria, fungal cells are seen to increase rather than decrease. The unpolluted soils had fungal cells density increased from 1.8 x 106 cfu/g soil (week 2) to 6.3 x 106 cfu/g (week 8). 0.25 percent pollution level had 1.17 x 106 (week 2) to 6.0 x 106 cfu/g soil. At 0.5 percent pollution level fungal cells density increased from 1.10 x 106 cfu/g to 7.03 x 106 cfu/g (week 6), and a slight decrease (6.0 x 106 cfu/g soil) week 8 and in 1.0 percent pollution level it increases from 9.33 x 105 cfu/g to 9.06 x 106 cfu/g. At the 1.5 percent pollution, increased by one log order of magnitude was observed (from 1.13 x 105 (week 2) to 6.03 x 106 cfu/g soil week 8). In this study, 16 fungal genera were identified, the most abundance was candida sp 20% followed by Mucor muccedo, 16.97%, and Penicillium notatium 12.73% Urease activity in all the treatment was not affected significantly. To degrade crude oil pollution in the soil, fungi should be used prominently for better results. Keywords: Crude Oil, Contamination, Microbial Community, Coastal Plain Sands.