Date Published: March 27, 2017
Publisher: Public Library of Science
Author(s): Qingguo Chen, Jingjing Li, Mei Liu, Huiling Sun, Mutai Bao, Pankaj Kumar Arora.
Five strains of bacteria, namely, Exiguobacterium sp. ASW-1, Pseudomonas aeruginosa strain ASW-2, Alcaligenes sp. ASW-3, Alcaligenes sp. ASS-1, and Bacillus sp. ASS-2, were isolated from the Zhejiang coast in China. The mixed flora of the five strains performed well with degrading 75.1% crude oil (1%, w/v) in 7 days. The calcium alginate—activated carbon embedding carrier was used to immobilize bacterial consortium. Immobilized cells performed better than free ones in variations of environmental factors containing incubated temperature, initial pH, salinity of the medium and crude oil concentration. The degradation process of crude oil by immobilized bacteria was accelerated compared with that of the free ones. Bacterial consortium showed better performance on biodegradation of normal alkanes than that of PAHs. Improvement of immobilization on the biodegradation efficiency of normal alkanes (31.9%) was apparently high than that of PAHs (1.9%).
Recently, with the development of offshore oil and transportation industry, the probability of spill oil is increasing on offshore oil platforms, oil tanker, and offshore oil facilities. Many oil drilling platforms are located in China’s offshore shipping and port areas, and they are not only the national strategic oil reserve base but also the oil reserve base of Chinese oil companies. Thus, the problem of oil leakage and pollution in coastal waters and ports has persisted for a long time. 
The microorganisms with efficient crude oil biodegradability, which were belonging to Exiguobacterium sp., Alcaligenes sp. Bacillus sp., or Pseudomonas aeruginosa, have been already reported in petroleum hydrocarbons biodegradation in marine enviroment. [26, 28, 30, 31] Biosurfactant generated from Exiguobacterium, Bacillus, and Pseudomonas aeruginosa were also found in previous study, [32, 33] which could enhance oil biodegradation efficiency.  The bacteria belonging to Exiguobacterium sp. and Bacillus sp. show strong biodegradation ability and have been reported in degrading chlorinated aromatic compounds that resistant to be biodegraded. [34–36] And in this study, these five strains belonging to bacterial species mentioned above all performed well in crude oil biodegradation, which got more than 50% of degradation efficiencies with 1% (w/v) crude oil. Flora can form a relative complete system for biodegradation. Through this way, a variety of enzymatic activities can aggregate for the expansion of the range of biodegradable petroleum fractions, and thus, the degradation activity can be improved. Bacterial consortia were formed up based on combinations of the five bacteria. However, not all the combinations showed cooperation actions in biodegradation, and the degradation efficiencies were lower than the single ones. The similar phenomenon was in previous study by Li et al. (2016).  That due to the competition between bacteria in a consortium result in the reduce of biodegradation efficiency.  The combinations of five strains performed the best cooperation actions, which got 75.1% of degradation efficiencies with 1% (w/v) crude oil. Crude oil degradation consortium has been carried out in previous studies. The comments cannot be carried out directly on the biodegradation ability of bacteria, due to various incubation conditions. In Varjani’s study, about 30% crude oil (3% v/v) biodegradation occurred in 12 d.  There is 51.9% crude oil (2% w/v) degraded after 7d of incubation in Li’s work.  However, the selected bacterial consortium in the present study performed effectively compared with previous studies. About 68% of biodegradation efficiency of crude oil (2% w/v) obtained after 1 week of cultivation.
In this study, five oil-degrading bacterial strains (ASW-1, ASW-2, ASW-3, ASS-1 and ASS-2) were isolated from oil polluted seawater samples nearby Zhejiang coast in China. They were affiliated to Exiguobacterium sp., Pseudomonas aeruginosa, Alcaligenes sp., Alcaligenes sp., and Bacillus sp., respectively. The mixed flora of the five strains showed the highest degradation efficiency of petroleum hydrocarbons of 75.1%.