Response Mechanisms Of Water Microbial Communities In Typical Bay To Oil Spills

Marine ecosystems in the waters of Jiaozhou Bay are threatened by accidental spills and long-term pollution due to the exploitation of petroleum hydrocarbons(HCs),especially in shallow waters.However,the response and degradation mechanisms of seawater microbial communities to HCs are still unknown.Therefore,this study used 16 s r DNA and metagenomic sequencing techniques in surface seawater to investigate the spatial and temporal distribution and functional characteristics of microbial communities,to investigate the response mechanisms of microbial communities to oil spill pollution and treatment,and to elucidate the molecular mechanisms of community succession and biodegradation during oil spill remediation.(1)The marine background study includes diversity and distribution of petroleum hydrocarbons,microbial communities and degradation functions.Marine water samples were collected in summer 2021 from areas at high and low risk of oil pollution,and found the levels of total petroleum hydrocarbons(TPH)showed a decreasing trend from the southeast to the northwest,with concentrations ranging from 0.06 mg/L to 0.51 mg/L.The species richness,composition and structure of the microbial community in the bay were similar,especially at HPA1,where the abundance and homogeneity were superior to other areas.The dominant bacterial species were concentrated in the Proteobacteria and Bacteroides phylum,such as Pelagibacteraceae,Flavobacteriaceae and Rhodobacteraceae as the dominant families in decreasing abundance.The total abundance of genes for degradation of alkanes,olefins,aromatic hydrocarbons and fatty acids in microbial communities in the high-risk area was significantly higher than that in the low-risk area,while the functions of long-chain fatty acids and phenylacetic acid degradation proteins were promoted.However,the low enrichment of genes for basal metabolic processes indicated that HCs enhanced microbial degradation of them while disrupting their original survival patterns.HPA1 is a priority because of the dominance of oildegrading bacteria and the number and distance of contamination sources.(2)To investigate the response of microbial communities to sudden oil spill contamination and treatment processes,an in situ microcosm simulation experiment was conducted(at HPA1).Changes with crude oil concentration,dispersant use and time were assessed using the dynamics of bacterial classification based on 16 s r DNA sequencing.The crude oil resulted in a high abundance of the genera Pseudohongiella,Cycloclasticus,Marivita,and C1–B045 from the Gammaproteobacteria and Alphaproteobacteria classes,suggesting for hydrocarbon degradation.However,the oil dispersant treatment was more advantageous for Pacificibacter,Marivita,and Loktanella.Dispersants had significantly stronger effects on bacterial community structure and degradation functions than oil,in addition to accelerating the succession rate of the bacterial community.Higher oil exposure corresponded to fewer dominant species with high relative abundance.(3)Both oil spills and dispersants clearly affect the diversity,succession rate and species composition of native microbes.However,research into the molecular mechanisms by which natural marine waters degrade oil pollutants is limited.In combination with metagenomics,differences in metabolic pathways and gene abundances of TPH under different conditions will be revealed.About 88% degradation of TPH was shown after 3 weeks of treatment.The positive responders to TPH were concentrated in the genera Cycloclasticus,Marivita and Sulfitobacter of the orders Rhodobacterales and Thiotrichales.The genera Marivita,Roseobacter,Lentibacter and Glaciecola were key degradation species when mixing dispersants with oil,and all of the above are from the Proteobacteria phylum,these dominant genera were recognized for their effective degradation of petroleum hydrocarbons after dispersant treatment.The enrichment analysis showed that the biodegradability of aromatic compounds,polycyclic aromatic hydrocarbon and dioxin were enhanced after the oil spill,and genes with higher abundances of bph Aa,bsd C,nah B,dox E and mhp D were found,but the basic metabolism-related mechanisms were inhibited.The dispersant treatment effectively stimulated the microbial degradation of TPH and then accelerated the succession of microbial communities.Meanwhile,functions such as bacterial chemotaxis and carbon metabolism(che A,fade J and fad E)were better developed,but the degradation of persistent organic pollutants such as polycyclic aromatic hydrocarbons was weakened.Potential indigenous microorganisms possess high diversity and abundance in the biodegradation of complex petroleum pollutants in study marine area.Specific microbial populations are often not unique in degrading targeted compounds,but HCs need to exist within a certain species range and concentration limits.Effective degradation and ecological restoration can be achieved through adaptive management.