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Biodegradation of used engine oil by novel strains of Ochrobactrum anthropi HM-1 and Citrobacter freundii HM-2 isolated from oil-contaminated soil

Ibrahim, HaythamM. M.
3 Biotech 2016 v.6 no.2 pp. 226
Citrobacter freundii, Ochrobactrum anthropi, biodegradation, bioremediation, cost effectiveness, gamma radiation, gas chromatography, inoculum, irradiation, liquid state fermentation, nucleotide sequences, oils, pH, polluted soils, ribosomal RNA, sequence analysis, temperature
Used engine oil (UEO) constitutes a serious environmental problem due to the difficulty of disposal off or reuse. Ten bacterial strains with biodegradation potential were isolated from UEO-contaminated soil sample using enrichment technique. Two strains which exhibited the highest degradation %, 51 ± 1.2 and 48 ± 1.5, respectively, were selected. Based on the morphological, biochemical characteristics and 16S rRNA sequence analysis, they were identified as Ochrobactrum anthropi HM-1 (accession no: KR360745) and Citrobacter freundii HM-2 (accession no: KR360746). The different conditions which may influence their biodegradation activity, including UEO concentration (1–6 %, v/v), inoculum size (0.5–4 %, v/v), initial pH (6–8), incubation temperature (25–45 °C), and rotation speed (0–200 rpm), were evaluated. The optimum conditions were found to be 2 % UEO, 2 % inoculum size, pH 7.5, incubation temperature 37 °C, and 150 rpm. Under the optimized conditions, strains HM-1, HM-2, and their mixture efficiently degraded UEO, they achieved 65 ± 2.2, 58 ± 2.1, and 80 ± 1.9 %, respectively, after 21 days of incubation. Biodegradation of UEO was confirmed by employing gas chromatography analysis. Gamma radiation (1.5 kGy) enhanced the degradation efficiency of irradiated bacterial mixture (95 ± 2.1 %) as compared to non-irradiated (79 ± 1.6 %). Therefore, strains HM-1 and HM-2 can be employed to develop a cost-effective method for bioremediation of used engine-oil-polluted soil.