Biodegradation of Used Engine Oil by a Methylotrophic Bacterium, Methylobacterium Mesophilicum Isolated from Tropical Hydrocarbon-contaminated Soil

Abstract

A Gram-negative facultatively methylotrophic bacterium putatively identified as Methylobacterium mesophilicum strain RD1 displayed extensive degradative ability on used engine oil (SAE 40W) in liquid cultures. The rate of degradation of used engine oil (1274.85 mg L−1) by the isolate, for the first 12 days and the last 9 days were 65 and 40 mg L−1 d−1, respectively. Gas chromatographic (GC) analyses of residual used engine oil revealed that 61.2% and 89.5% of the initial concentration of the used engine oil were degraded within 12 and 21 days. GC fingerprints of the used engine oil after 12 days of incubation showed total disappearance of C15, C23, C24, C25, and C26 hydrocarbon fractions as well as drastic reductions of C13, C14, C16, and PAHs fractions such as C19-Anthracene and C22-Pyrene. At the end of 21 days’ incubation, total disappearance of C17-pristane, C22-pyrene, one of the C19-anthracene, and significant reduction of C18-phytane (96.8%) fractions were observed. In addition, less than 10% of Day 0 values of medium fraction ranges C13, C14, and C16 were discernible after 21 days. This study has established the potential of Methylobacterium mesophilicum strain RD1 in degradation of aliphatic, aromatic, and branched alkane components of used engine oils.