Insights into the microbial diversity and functionalities of potential hydrocarbon-degrading bioremediation agents in oil spill sludge of Assam, India.

Oil spill contamination poses a significant threat to environmental and ecological health, particularly in crude oil-rich regions such as Assam, a north-eastern state of India. This study explores the microbial diversity and functional potential of hydrocarbon-degrading bacteria in crude oil-contaminated sludge. Sludge samples were collected from three contaminated sites in Assam and analyzed for microbial diversity by culture dependent and independent (using 16 S rRNA amplicon sequencing) approaches. Metagenomic analysis revealed a diverse microbial community, with Proteobacteria and Planctomycetes dominating the metagenomes. Seven bacterial isolates, including Diaphorobacter nitroreducens, Lysinibacillus capsici, and Pseudomonas otitidis, were isolated and identified as potential hydrocarbon degraders. The isolates were screened and evaluated for biosurfactant production, hydrocarbon adhesion, and key enzymatic activities involved in degradation. These isolates exhibited significant biosurfactant-producing abilities, with Diaphorobacter nitroreducens MBRG1 showing the highest emulsification index (79%) and strong adherence to hydrocarbons. The enzymatic activities of alkane hydroxylase and alcohol dehydrogenase confirmed the metabolic capabilities of the isolates in hydrocarbon degradation. Optimal growth conditions for biosurfactant production were determined to be pH 7, 30 °C, 2% sucrose as the carbon source, and 3% yeast extract as the nitrogen source. The study highlights the potential of these indigenous bacterial isolates in bioremediation strategies to mitigate oil contamination. Future studies should focus on large-scale bioreactor studies, field trials, and strain improvement of these bacteria to enhance their degradation efficiency and adaptability to varied environmental conditions.