Identification and biodegradation characteristics of oil-degrading bacteria from subtropical Iriomote Island, Japan, and tropical Con Dao Island, Vietnam

Indigenous oil-degrading bacteria (ODB) were screened from two islands, Iriomote, Japan and Con Dao, Vietnam. These islands are considered predicted contamination sites from oil spillage on a nearby busy transportation route. The aim of this study was to compare the degradation abilities of bacterial isolates from the two different study areas for crude oil, n-alkanes, and polycyclic aromatic hydrocarbons. Comparing the two study areas, the numbers of the total bacteria and ODB showed the same distribution tendencies. There were no differences between Iriomote and Con Dao in the counts of the total bacteria and ODB in sediment samples, while those in seawater samples were statistically lower for Iriomote than for Con Dao. A total of 45 isolates, 25 from Iriomote and 20 from Con Dao, belonging to 18 genera, were isolated. Among 11 genera detected on Iriomote, the dominant genera were Achromobacter, Pseudomonas, and Ochrobactrum. Among 11 genera from Con Dao, the dominant genera were Pseudomonas and Microbacterium. The degradation ability of the isolates was studied for crude oil, two kinds of n-alkanes, and two kinds of polycyclic aromatic hydrocarbons (PAHs). The numbers of the isolates that degraded more than 50 percent of the crude oil and n-alkanes and 25 percent of the PAHs present in the media were higher for Iriomote (3, 11, and 2, respectively) than for Con Dao (2, 4, and 1, respectively). It is noteworthy that the isolates of Pseudomonas putida and Ochrobactrum anthropi could degrade more than 40 percent of the oil and n-alkanes and more than 25 percent of the PAHs present in the media.