Isolation, Identification, Characterization, and Screening of Hydrocarbon-Utilizing Bacterial and Fungal Isolates from Composted Organic Materials

Abstract

Bacteria and fungi from composted organic materials (COMs) are diverse, readily cultivable, and promising for bioremediation of hydrocarbon-polluted environments. This study isolated and identified microbial species from COMs and evaluated their hydrocarbon-degradation potential using contaminated soils from four sites in Sokoto Metropolis, Nigeria. Viable counts of (9.37 ± 0.67) × 10⁶ CFU/g for bacteria and (5.1 ± 3.5) × 10³ CFU/g for fungi were recorded. Six bacterial species were isolated, with Bacillus cereus (30%) predominant, followed by Pseudomonas sp. and Bacillus anthracis (20% each); Bacillus megaterium, Pseudomonas aeruginosa, and Bacillus subtilis each accounted for 10%. Biochemical tests confirmed broad metabolic capabilities, including starch hydrolysis, sugar fermentation, and catalase activity. Fungal characterization identified Saccharomyces cerevisiae as dominant (50%), followed by Aspergillus niger and Fusarium solani (16.7% each), with Aspergillus fumigatus and A. flavus at 8.3% each. S. cerevisiae formed smooth, cream-coloured colonies, while A. niger and F. solani showed distinct mycelial morphologies. Hydrocarbon utilization by bacterial isolates, tracked over four days via OD₆₀₀, showed Bacillus subtilis (0.21) and Pseudomonas sp. (0.20) as the most active degraders, followed by P. aeruginosa (0.178), B. cereus (0.16), B. anthracis (0.15), and B. megaterium (0.134). Fungal hydrocarbon utilization over 12 days showed A. niger (OD₆₀₀ = 1.8) and A. fumigatus (OD₆₀₀ = 1.5) with the highest growth, indicating strong degrading capacity, while A. flavus, F. solani, and S. cerevisiae showed moderate activity (OD₆₀₀ = 0.7–0.9). These findings underscore the potential of COM-derived microbial consortia for eco-friendly bioremediation of hydrocarbon-contaminated soils.