Assessing Earthworm Influence on Remediating Potentials of Soil Micro-Organisms, and Bioavailable Hydrocarbon Pollutant in the Niger Delta, Nigeria

In the Niger Delta region of Nigeria, oil explorations and exploitations abound, causing environmental pollution with serious consequences on soil ecosystem and its biodiversity. In spite of the relationship between microbes and fauna in soil ecosystem, such that both organisms can metabolize certain range of petroleum hydrocarbon substrates with the fauna influencing the remediation potentials of bacteria, yet soil fauna is still not fully considered in bioremediation. The influence of earthworm;Lumbricus terrestris on the remediating potentials of soil bacteria in petroleum hydrocarbon contaminated soils was investigated. Eighteen pots were filled with 700 g of soil each, with nine treated with mixture of 3 levels crude oil and remediated with earthworm, while the other nine had no earthworm. The total petroleum hydrocarbon (TPH), soil physical, nutrient compositions, and TPH degrading bacteria biodiversity were determined before contamination or commencement of study and thirty days after. The results showed a decrease in TPH concentration of 55.58%, 62.57% and 67.07% in 1 ml, 2 ml and 3 ml crude oil contaminated soil, respectively. Species richness and abundance of bacteria organisms increased with high relative abundance in soils remediated with earthworms, hydrocarbon utilizing bacteria increased from less than 0.1 cfu/g to 0.4 cfu/g, and total heterotrophic bacteria 1.6 cfu/g at the end of the study. Earthworms increased rate of remediation potentials of bacteria, such that within 30 days post remediation treatment, 34.14% of reduced concentration was achieved over soil samples without earthworms at 3 ml, and 25.14% at 2 ml concentration. Reduction in pH levels in remediated soils was between 6.39 to 6.17 and 6.74 to 6.72 in unremediated soils, while moisture content was 6.73% to 6.77% unremediated and 5.85% to 6.62% in earthworm remediated soils. Total organic carbon, nitrates in soils inoculated with earthworms were lower in concentration than those without earthworms. Reverse was the case with potassium, phosphate and phosphorous concentrations which were above those without earthworms. Results indicate statistically, significant difference between reduction in TPH in earthworm remediated soils and unremediated soils, pointing out that earthworm is a good candidate for facilitation of bacteria remediation-petroleum hydrocarbon contamination.

Impacts of n-alkane concentration on soil bacterial community structure and alkane monooxygenase genes abundance during bioremediation processes

Petroleum hydrocarbons,mainly consisting of n-alkanes and polycyclic aromatic hydrocarbons(PAHs),are considered as priority pollutants and biohazards in the environment,eventually affecting the ecosystem and human health.Though many previous studies have investigated the change of bacterial community and alkane degraders during the degradation of petroleum hydrocarbons,there is still lack of understanding on the impacts of soil alkane contamination level.In the present study,microcosms with different n-alkane contamination(1%,3%and 5%)were set up and our results indicated a complete alkane degradation after 30 and 50 days in 1%-and 3%-alkane treatments,respectively.In all the treatments,alkanes with medium-chain length(C_(11)-C_(14))were preferentially degraded by soil microbes,followed by C27-alkane in 3%and 5%treatments.Alkane contamination level slightly altered soil bacterial community,and the main change was the presence and abundance of dominant alkane degraders.Thermogemmatisporaceae,Gemmataceae and Thermodesulfovibrionaceae were highly related to the degradation of C_(14)-and C_(27)-alkanes in 5%treatment,but linked to alkanes with medium-chain(C11-C18)in 1%treatment and C21-alkane in 3%treatment,respectively.Additionally,we compared the abundance of three alkane-monooxygenase genes,e.g.,alk_A,alk_P and alk_R.The abundance of alk_R gene was highest in soils,and alk_P gene was more correlated with alkane degradation efficiency,especially in 5%treatment.Our results suggested that alkane contamination level showed non-negligible effects on soil bacterial communities to some extents,and particularly shaped alkane degraders and degrading genes significantly.This study provides a better understanding on the response of alkane degraders and bacterial communities to soil alkane concentrations,which affects their biodegradation process.