Effect of Pristine Soil Addition and Cow Dung Treatment on the Community Structure Post Bioremediation

Abstract

The pollution of crude oil on agricultural soil has become a menace in the world today. The ecologically friendly approach of restoring this polluted soil back to its original state is pertinent. In this study, 1000 g of crude oil polluted soil was amended with 12.5g of cow dung and 500 g of unpolluted soil, 1000 g of polluted soil with crude oil without cow dung amendment, and 1000 g of unpolluted soil without crude oil and cow dung amendment was the control. The setup was monitored for their physicochemical parameters such as total petroleum hydrocarbon (TPH), polyaromatic hydrocarbon (PAH), temperature, pH, electrical conductivity (Ec), and total nitrogen. The microbiological characterization for viable and culturable was done for total heterotrophic bacteria (THB) and hydrocarbon utilizing bacteria (HUB) while non-culturable but viable characterization was done using metagenomics-shotgun analysis to compare the changes in community structure before, during, and after remediation. The THB observed in the samples were 1.9 x 107, 1.3 x 103, 4.0 x 106, 3.58 x 108, 2.15 x 109 while HUB was 1.6 x 103, 1.0 x 101, 1.67 x 103, 2.5 x 104, and 3.55 x 104 respectively for A (unpolluted soil), B (polluted soil without 1.67 x 103, 2.5 x 104, and 3.55 x 104 respectively for A (unpolluted soil), B (polluted soil without treatment), J1 (month 1), J2 (month 2), and J3(month 3). Over 90 % removal of the TPH was achieved by the treatment. The molecular characterization showed that Proteobacteria was the dominant phylum identified in the pristine soil, but Actinobacteria were the most dominant in the soil with treatment. Nitrogen-fixing Bradirhizobium elkanii was found to be 0.66%, 5.11%, 10.43% before pollution, during natural attenuation, and with unpolluted soil addition with cow dung amendment. Denitrifying Nocardiodes daejeonensis and Nocardiodes terra were identified at 0.1 and 2.0% respectively only three (3) months after the end of the bioremediation treatment.