Rhizosphere and Hydrocarbon Utilizing Bacteria of Wetland Plants in Oil Polluted Areas of the Niger Delta Region, Nigeria

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Abstract

The study investigated the presence of heterotrophic bacteria and petroleum hydrocarbon utilizing bacteria (using Minimal Salt Medium) in the rhizosphere of wetland plants in six-month old and twelve-month old petroleum-contaminated sites and an uncontaminated site in Oloibiri Oil Field, Ikarama and Otuoke respectively, Bayelsa State, Nigeria. Nineteen species of wetland plants were identified and three unidentified species. Plant species common to all the three sites are Commelina benghalensis, Chromoleana odorata and Aspilia Africana. Ipomoea involucrata, Kyllinga species and Ageratum conyzoides are peculiar to the petroleum-contaminated sites. Other plant species are site specific. Bacteria isolated belong to the phyla Proteobacteria, Bacteroidetes and Firmicutes with the γ-Proteobacteria and particularly Pseudomonas spp. dominating in all the sites, both as heterotrophic and hydrocarbon utilizing bacteria. More heterotrophic bacterial species occurred at the uncontaminated site (38.46%) than the contaminated sites (30.77% each). Hydrocarbon utilizing bacterial species diversity was greater at the twelve-month old contaminated site (44.44%), followed by the uncontaminated site (38.89%) while fewer species (16.67% Pseudomonas spp) were at the six-month old site. The total heterotrophic bacterial counts (THB) of the soils were 1.37 x 108 – 2.80 x 108 cfu/g, the hydrocarbon utilizing bacterial counts (HUB) were 4.00 x 107 – 1.33 x 108 cfu/g with the petroleum-contaminated sites having higher counts. The rhizosphere bacterial counts were 1.25 x 107 – 1.03 x 108 cfu/g (THB) and 1.20 x 107 – 3.20 x 107 cfu/g (HUB), with the uncontaminated site having the most. The findings show high numbers of HUB in the uncontaminated soil indicating soil pollution. These findings may be of immense help in planning bioremediation strategies but further investigation on the role of the individual plants and rhizosphere populations would be required

Keywords: Heterotrophic bacteria, Hydrocarbon utilizing bacteria, Petroleum, rhizosphere, Wetland

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