16S rRNA gene sequencing of aged oil -contaminated soil samples during the bioremediation process

The goal of the study was to study the degradation of total petroleum hydrocarbons (TPHs), polycyclic aromatic hydrocarbons (PAHs) and understand the changes in the bacterial community in soil piles during nine months of pilot-scale bioremediation process of aged soil contaminated with crude oil. The soil samples were collected from a moderately contaminated stockpile (50,000 mg per kg TPH) subjected to a bioremediation experiment. This pile was aerated by mixing and fertilized with a combination of inorganic nutrients (urea; triple phosphate) and compost (50 kg per m3) corresponding to a total amount of C-N-P 50-1-1 to enhance the growth of the indigenous microorganisms. A control soil was taken from an area directly adjacent to the excavated contaminated soil at a depth of 20-30 cm. This soil was not subjected to bioremediation treatment. Three samples were collected from the contaminated stockpile immediately after treatment and 3, 6, and 9 months after treatment. Each sample was prepared by pooling and homogenizing 5 subsamples corresponding to 5 locations randomly chosen along the pile. The soil samples were sieved through a 2mm pore size sieve and the total DNA was isolated. The microbial consortium associated with oil degradation at each interval was revealed through 16S rRNA gene based next-generation sequencing.