Biodegradation Potential of Bacterial Isolates from Crude Oil Contaminated Soil Samples from Gelegele River, Edo State

Abstract

The dependency on fossil fuels as energy source has resulted in
serious environmental issues in recent times. Bioremediation is an
efficient, economic and environmentally friendly method of
treatment. The purpose of this study was to determine the degradative
potential of bacterial isolates from soil samples collected from
Gelegele river. Eight (8) soil samples were collected from eight
sampling locations around the flow station at Gelegele River. The
physiochemical studies were carried out according to the methods of
Association of Official Analytical Chemist (A.O.A.C) for the
determination of the soil physicochemical parameters. Standard
microbiological techniques were used for the morphological and
biochemical analysis. Molecular characterization of the bacterial
isolates was carried out using 16S rRNA, and shake flask technique
was used for the bioremediation studies. Gas chromatography with
flame ionization detector (GC-FID) method was used for the
determination of total petroleum hydrocarbon. The physiochemical
parameters, pH, electrical conductivity (EC), carbon showed
significance (p˂0.05) with respect to normal control. The total
petroleum hydrocarbon (TPH) was recorded above the 1,000 mg/kg
permissible limit by World Health Organization (WHO) and United
States Environmental Protection Agency (USEPA) for hydrocarbon
contaminated soil. The total heterotrophic bacterial counts ranged
from 2.3 ± 3.5 x 104 cfu/g - 5.2 ± 3.5 x 104 cfu/g, while the total
hydrocarbon utilizing bacterial counts ranged from 0.3 ± 0.01 x 103
cfu/g - 3.6 ± 2.60 x 103 cfu/g. The screening test revealed that out of
the seven bacterial isolates screened for hydrocarbon utilization, six
had the potentials to utilize hydrocarbon as carbon and energy
sources. The bioremediation studies revealed changes in pH, which
ranged from 5.0 - 7.3, temperature 31.0 0C - 33.2 0C and optical
density 0.1300 - 1.236, of the mineral salt broth. Bacterial isolates
showed degradation of aliphatic components of crude oil with
respect to normal control. Molecular characterization revealed the
bacterial isolates to include Citrobacter freundii Citrobacter cronae,
Bacillus cereus, Citrobacter sp., Citrobacter cronae and Providencia
vermicola. This study shows that the identified bacterial isolates may
constitute potential isolates for biotechnological application in
environmental clean-up of petroleum hydrocarbon.