Study On PAHs--Biodegrading Bacteria In Antarctic Soil: Isolation, Characterization And Degrading Genes Detection

Contaminant-removing bacteria are important for us in learning the influence ofhuman activity on Antarctic environment and of practical use for bioremediation incold regions. In this study, the investigation on the PAH-degrading bacteria from theAntarctic region and normal temperature environment was conducted , and the resultshowed that the Pseudomonas spp was dominant in the Antartic area, where HGTplayed an important role in situ bacteria biodegradation. The main aspects as the following: 1.Isolation of degrading bacteria In this report, twenty-two PAHs-degradingstrains were isolated from Antarctic soils at several sites by enrichment at lowtemperatures with naphthalene or phenanthrene as the sole carbon source; meanwhile,two phenantherene-degrading bacteria were isolated from normal environment. 2. Identification of degrading bacteria As detected by 16S rDNA sequencingand phylogenetic analysis, the two strains WSCII and WSCIII from normalenvironment belonged to Sphingomonas and Pseudomonas, respectively; all but oneof the obtained strains from the Antarctic belonged to Pseudomonas and the one wasin the genus of Rahnella and of 97% similarity with R. aquatilis. Most of thesePseudomonas strains were in the same phylogenetic groups with other reported coldtolerant species; only four strains close to mesophilic species. The optimal growthtemperature of these strains was from 16℃ to 20℃ as detected with six randomlyselected stains. 3. Determination of bacteria degrading rate The degrading curves of the twomesophilic strains were determined by HPLC, and the results showed that just in 4days more than 70% phenanthrene in medium was metabolized. As to the obtained 22Artarctic strains, all showed high efficiency in naphthalene degradation at 4℃, andsome strains showed phenanthrene degrading ability with relatively low efficiencycompared to naphthalene,but all of them could not degrade alkylhyrocarbon. 4.Detection of degrading key-enzyme genes and HGT All the genomic DNAof the 22 Antarctic strains and one normal temperature strain as the template were VIamplified for alpha subunit gene of naphthalene-dioxygenase, and the result showedthat seventeen strains gave positive results and other six showed no signals. Further,sequencing and alignment analysis showed the 17 obtained NDO genes could begrouped into two clusters, and one was of above 98% similarity, the other withabove 99% similarity, but only 94% similarity between the two clusters. Interestingly,it was found that distant-related strains in phylogenetic tree hosted similar even sameNDO genes, indicating that horizontal gene transfer possibly happened in Antarcticregion. 5. The activity of degrading enzyme Furthermore, the WSCII and WSCIIIdioxygenase specific activity in different carbon sources were determined, and thehighest activity showed that the enzyme express induced by specific substrate. Andthe optimal activity temperatures of NDO in the cold-adapted LCY12, LCY16 andmesophilic WSCIII were all at about 30℃ examined by indigo transformation.Together, results of this report suggested that Pseudomonas bacteria were crucial inPAH biodegradation in Antarctic soils, and the ability might be derived fromhorizontal gene transfer.