The Research Of Temporal And Spatial Variations Of Bacterial Community After “7.16” Oil Spill In Dalian

The rapid development of marine transportation has resulted in a mount of marine pollution accident. The Dalian xingang oil spill, occurred on July 16, 2010, was the largest in China history. After the accident, a succession of investigation in Dalian bay area was carried out for five years. With the aim to understand the effects of the oil spill accident on the marine ecological environment, the correlation between bacterial abundance and total petroleum hydrocarbon(TPHs) content, microbial community structure and function diversity were studied.After the oil spill, the abundance of heterotrophic bacteria in sediments and petroleum hydrocarbon-degrading bacteria was studied using culturable method for five years. We explored the correlation between bacterial abundance and environmental chemistry factors, combined with the distribution of TPHs content and environmental factors. The TPHs concentration in surface seawater reduced from 0.22~0.67 mg/L in September 2010 to 0.0025~0.05 mg/L in May 2012, with the seawater quality changing from the third to the first seawater quality standards. The TPHs concentration in surface sediments collected along the coastal sites BQ012 reduced from 7 133 μg/g in December 2011 to 926 μg/g in 2014, indicating the sediments quality recovered to the first quality standards in 2014. The abundance of heterotrophic bacteria and petroleum hydrocarbon-degrading bacteria reached to 105 CFU/mL and 104 CFU/mL, respectively. After 5 years, bacterial abundance decreased 1~2 magnitudes. The ratio of hydrocarbon-degrading bacteria and heterotrophic bacteria(HDB/HB) in surface seawater was significantly correlated with petroleum hydrocarbon concentration(P<0.01). There were no significant correlations between bacterial abundance and concentrations of nutrient salt and dissolved oxygen. Therefore, the value of HDB/HB is recommended to serve as an index of petroleum hydrocarbons pollution levels in the seawater environment.In this paper, microbial community structure of the sediment in Dalian bay was investigated using the Illumina Miseq high-throughput sequencing method. The microbial communities were grouped into 50 different bacterial phyla. The phylum Proteobacteria dominated in 15 sediment samples, followed by the Bacteroidetes, Firmicutes, Acidobacteria, Chloroflexi, Planctomycetes, Actinobacteria and Verrucomicrobia. Among them, the Delta-, Gamma- and Epsilonproteobacteria were detected by 31.35%, 26.31% and 5.79%, respectively. Deltaproteobacteria and Gammaproteobacteria dominated in most of the samples. The relative abundance of the Epsilonproteobacteria was higher in the site with high concentration of oil than other sites. The hydrocarbon-degrading bacteria accounted for higher proportion in the total bacterial community. There were higher proportion of phylogenetic groups at family level associated with aerobic hydrocarbon-degradation found in Dalian bay sediments, which decreased with time, including Pseudomonadaceae, Piscirickettsiaceae, Thiotrichaceae, Halomonadaceae, Oceanospirillaceae, Oleiphilaceae, Vibrionaceae, Alteromonadaceae, Aeromonadaceae and Colwelliaceae, etc.Bacterial community diversity results showed that bacteria Tag sequence number decreased gradually from offshore to the far shore, while OTU number tended to increase. Bacterial diversity increased with the decrease of concentration of petroleum hydrocarbon. there were higher bacterial abundance and high levels petroleum hydrocarbon in offshore site, and bacterial diversity was relatively lower than other sites. The influence of various environmental factors on bacterial community structure was as follow: TPHs > TOC > PAH > S. In conclusion, oil composition could be the main factor affecting functional structure and composition of microbial community.The abundance of bacterial 16 S rRNA and alkane-degrading genes in the sediment were analyzed using the real-time PCR. The results showed that copies of the 16 S rRNA gene tended to be in the range of 8.30×108~1.10×1010 copies/g, and the total number of bacterial cells per gram is in the range of 2.01×108~2.66×109 in sediments, higher than the number of culturable heterotrophic bacteria. There were significant correlations between 16 S rRNA gene copies and total petroleum hydrocarbon(P<0.05), indicating that the petroleum hydrocarbon content was the main factor which affect 16 S rRNA genes copies. Alkane oxygenase(AlkB) gene copies tended to be in the range of 5.32×106~6.32×107 copies/g.This study will assist us to understand the distribution of bacterial community and the response mechanism of bacterial community composition to the oil pollution. Furthermore, it will provide basic data for us to assess the effect of petroleum hydrocarbon on degradation bacteria.