Potential of biofilm producing bacteria in remediation of crude oil polluted soil

Abstract

Bioremediation is an environmentally friendly approach to remediate polluted environments. This study aimed to evaluate the potential of biofilm-producing bacteria for the remediation of crude oil-polluted soil. The crude oil-polluted soil sample was collected from Biara, in Gokana Local Government Area of Rivers State, Nigeria. The soil was analyzed using standard procedures. The hydrocarbon-utilizing bacterial isolates were screened for biofilm production (BP), and those positive for BP were identified using biochemical methods. Three strong biofilm-producing bacteria (Klebsiella, Pseudomonas and Bacillus spp.) were selected and used for laboratory-scale bioremediation experiments. The experiments were carried out in eight microcosms, where the isolates were used singly and in combination, representing the various treatment options and the control (sterile soil). The setups were maintained for 56 days; samples were taken out every 7 days to analyze for the total hydrocarbon content (THC) using a spectrophotometer, nitrate, phosphate, total heterotrophic bacteria (THB) and hydrocarbon-utilizing bacteria (HUB). The results obtained revealed that THC, nitrate, pH and phosphate of the crude oil polluted soil were 18,403±3, 627, 92.6±0.3, 6.11 and 4.36±0.12 mg/kg, respectively on day 1. The THB and HUB populations in the soil were 1.68±0.07 × 107 and 1.54±0.06× 103 CFU/g. THB and HUB in the microcosms on days 1 to 56 ranged from 1.02±0.01 to 9.65±0.21 × 108 and 7.00±1.41 × 103 to 5.20±0.14 × 108 CFU/g, respectively. A general decrease in THC, nitrate and phosphate from days 1 to 56 in all the microcosms, was observed. The extent of hydrocarbon degradation (EHD) in the microcosms at day 56 was observed to be highest for the single isolates than the combinations, with Bacillus sp having the highest EHD of 97.40%, Klebsiella sp at 96.0% and Pseudomonas sp at 95.60%. It was observed that for the combinations, Klebsiella plus Pseudomonas gave 95.0%, Pseudomonas plus Bacillus gave 93.9%, and Klebsiella plus Bacillus gave 89.34%. The concentration of crude oil degraded is statistically significant when compared to the control, but when the EHD of the single isolates were compared, there was no significant difference between the results. When the three isolates were combined, 85.69% EHD was observed, while the control gave the least EHD of 12.0%. This study has shown that BPB has the potential to biodegrade crude oil pollutants in soil and may be deployed for the bioremediation of crude oil-polluted soil.

Keywords: Bioremediation, potentials, biofilm-producing bacteria, polluted soil, consortium.