Diversity Of PAH-Degrading Bacteria In Deep Water Of Indian Ocean, Classification And Degradation Pathway Research Of Some Novel Bacteria

Polycyclic aromatic hydrocarbons (PAHs) were are ubiquitous compounds containing two or morebenzene rings. The presence of PAHs in the environment is a considerable public healthhazard because of their intrinsic chemical stability, high recalcitrance to different types ofdegradation and high toxicity to living organisms.The principle processes for theirsuccessful removal are currently believed to be microbialtransformation and degradation.But bacteria involved in organic pollutant degradation in deep sea environments are largelyunknown.This study aimed at finding bacteria can utilize PAHs, identifying the functional genesinvolved in the biodegradation, and elucidating PAHs metabolism pathway.The mainresults were as follows:1.In this report, the diversity of polycyclic aromatic hydrocarbon (PAH)-degradingbacteria in the deep sea water column of 4766m water depth was analyzed. The samplingsite was on the southwest Indian Ridge (IR), nearby where several hydrothermal ventslocate. After enrichment with a PAH mixture (phenanthrene, anthracene, fluoranthene andpyrene)and single PAH, 9 PAH- and 9 phenanthrene-degrading bacterial consortia wereobtained, one at each sampling depth ranging from 20m to 820m above the bottom. Bothculture-dependent and independent methods revealed many new bacteria involved in PAHdegradation, which significantly differed with those previously reported. Statistically, alphaand gamma subclasses of Proteobacteria were confirmed as the major group in thecommunities; Actinobacteria, the CFB group and the Firmicutes bacteria were additionallydetected. Although community structures dynamically changed spatially and temporally,bacteria closely affiliated to Alcanivorax, Novosphingobium, Rhodovulum, Bartonella,Arthrobacter and Azospirillum most frequently occurred. In addition, many bacteria had thehighest similarities ranging from 88%to 97% with 16S rRNA gene sequences retrievedfrom GenBank database. However, only part of the detected bacteria has not been isolated.Among those purified isolates, more than half were confirmed to grow with the PAHsmixture.2.A novel Gram-negative, PAH-degrading bacterium isolated from deep sea water of Indian Ocean was studied phenotypically, genotypically and phylogenetically. The isolatecan utilize several polycyclic aromatic hydrocarbons. Analyses of 16S rRNA genesequence, DNA base composition and whole-cell fatty acid profile revealed that the isolateis a member of the genus Novosphingobium. However, the sequence similarity of its 16SrRNA gene to those of known members of this genus Novosphingobium ranged only from92.1%to 96.0%,implying that the isolate is distinctive. The results of DNA-DNAhybridization experiments and physiological characterization also indicate that the isolaterepresents a novel Novosphingobium species, for which the name Novosphingobiumindicum sp. nov. was proposed. The type strain is H25. In addition, two fragments whichcontained theαandβsubunit of dioxygenase gene and its upstream and downstreamsequences were obtained by PCR.3.A bacterium named PTG4-1 was isolated from deep-sea sediment at the site DY10517A IR-TVG4 of Indian Ocean. According to its morphology, physiology, fatty acidcomposition and 16S rRNA gene sequence, the novel strain fitted well into the genusPseudoruegeria, but could be easily distinguished from all other known Pseudoruegeriaspecies described to date. The name Pseudoruegeria indicum sp. nov. is proposed, with thetype strain PTG4-1.It is able to degrade a wide range of polycyclic aromatic hydrocarbons(PAHs). To get insight into the mechanism of biodegradation, the intermediates offluoranthene, phenanthrene and dibenzothiophene degradation were examined withGC-MS. And their biodegradation pathways were also suggested.For its broad utilization of PAHs and adaptability in marine environment, such a strainmay be useful for bioremediation applications in polluted oceans. Further analysis is on theprogress.In summary, this report revealed for the first time that PAH degrading bacteria arewidespread in the deep-sea water column. Evidently, they take part in the carbon recyclingof marine ecosystem by mineralizing the persistent organic compounds, with minute bodysize but huge effects, considering the oligotrophic and boundless deep sea environments.