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Microbial degradation of petroleum hydrocarbons is one of the important pathways in the natural decomposition process. Four potential oil degrading bacteria were isolated from the coastal waters and sediments in Sri Lanka and identified as Bacillus cereus, Enterobacter sp., Enterobacter ulcerans and Micrococcus sp. by 16S rRNA sequencing. The highest degradation percentage of crude oil was detected at 14 days of incubation by B. cereus (84 %). The remaining strains of Enterobacter sp. (80 %), Micrococcus sp. (74 %) and E. ulcerans (74 %) were also detected as active degraders. The lowest half life time was recorded for Enterobacter sp. at 6 days of incubation, while the half life time of B. cereus and Micrococcus sp. was 7 days, and 10 days for E. ulcerans. The population densities of bacteria were proportional to their degradation rates. Different emulsification index values were detected starting from 18 ‒ 65 % for B. cereus, 48 % for Enterobacter sp., 38 % for Micrococcus sp., and 38 % for E. ulcerans at 14 days of incubation. The FTIR spectrum analysis revealed that the peak area relevant to the C-H groupʼs stretching (2850 ‒ 3000 cm-1) decreased with incubation from 0.115 to 0.04 for B. cereus and from 0.115 to 0.08 for Enterobacter sp.. The infrared absorption wavelength range of 1455 ‒ 1500 cm-1 relevant to deformations of C-H bonds to CH2, CH3, and cyclohexanes decreased from 0.08 to 0.018 in B. cereus and from 0.08 to 0.04 for Enterobacter sp.. Among the bacterial isolates B. cereus was identified as the most efficient hydrocarbon degrader in the present study.
