RESUMO
The bio-stimulation of hydrocarbon degrading microbial population in soil using agricultural wastes was carried out. Top soil (0-25 cm depth) from three points were bulked to form composite soil samples, 6 kg each of the composite soil sample was weighed and transferred into 150 plastic buckets with drainage holes at the base. The soil in each plastic bucket was spiked with 300 ml crude oil and amended with different concentrations of agro-wastes and allowed for duration of 30, 60 and 90 days. The soil samples were then collected and analysed for both total heterotrophic bacterial counts and crude-oil utilizing bacterial counts. Data collected were subjected to a three-way analysis of variance and significant means were separated using Least Significant Difference Test at 5% probability level. The result showed that the application of the amendments increased the bacterial counts in the soil at different treatment levels. However, a higher proliferation rate was observed with bacteria counts exposed to higher waste concentrations compared to their counterparts exposed to lower waste concentrations. The phylogenetic relationship of the hydrocarbon degrading bacterial species shows that the identified bacteria were in two clusters: cluster 1 consist of Bacillus cereus, Bacillus thuringiensis, Bacillus altitudinis, Pseudomonas aeruginosa, Proteus mirabilis and Proteus penneri, while cluster 2 consist of Serratia marcescens, Providencia rettgeri and Enterobacter asburiae. The bacterial species obtained shows a greater relationship, this imply that the similarity of the bacterial species could be the reason for their high proficiency in degrading the hydrocarbons in the soil.
RESUMO
A large amount of crude oil is spilled annually into the terrestrial and aquatic environments in Nigeria. This tends to upset the natural equilibrium of the marine environment as a microbial habitat. Thus, there is a need to evaluate the effect of exposure to crude oil on bacterial load and diversity using Iko River and Odoro Ikot pond as the study and pristine sites respectively. The bacterial isolates were molecularly identified using the 16S rRNA sequencing protocol. The total heterotrophic bacterial count (THBC) in the surface water (SW), sub-surface water (SSW) and sediment segments of Iko River ranged from 2.23±0.87 to 9.67 ± 0.43 x 106 CFU/ML while the THBC in the SW, SSW and sediment segments of the pristine site (Odoro Ikot pond) ranged from 1.87±0.53 to 4.8± 0.04x106 CFU/ML. The sediment had a significantly higher (P<0.05) THBC than the water segments (SW and SSW) in both Iko River and Odoro Ikot pond. The hydrocarbon utilizing bacteria (HUB) count in Odoro Ikot pond ranged from 0.40 ± 0.01 to 1.10 ± 0.03 x 106 CFU/ML while the HUB count in Iko River ranged from 0.53 ± 0.02 to 0.93 ± 0.04 x 106 CFU/ML, making Iko River have a higher number of total heterotrophic bacteria and hydrocarbon utilizing bacteria than Odoro Ikot pond. The Proteobacteria isolates had the highest bacterial diversity (77%) while members of the Firmicutes phylum had a 23% bacterial diversity. However, higher bacterial count and diversity were obtained from the sediment segment than from the water segments in both Iko River and Odoro Ikot pond implying that the sediment is more favourable for bacterial growth. Although the bacterial profile was affected by exposure to crude oil, there were variations in the phylogenetic diversities obtained from the different water segments attributable to crude oil concentration.