Identification And Characterization Of New Type Of Bacteria Degrading Polyvinyl Alcohol From Activated Sludge

Poly(vinyl alcohol)(PVA),a water soluble polymer prepared by the hydrolysis of poly(vinyl acetate),is widely used in industrial applications,such as adhesives and sizing agent in textiles.It has also been used for cell immobilization.Recently,PVA has attracted attention as the biodegradable backbone in sugar and fatty acid branched polymers.PVA is produced in greater quantities than any other water-soluble synthetic polymer.The world production of PVA is about 650000 tons per year and the large amount of used and discarded PVA has become a significant waste problem.PVA is difficult to be degraded in natural environment and must be removed from the waste water before discharge.The little information available regarding microbial degradation of PVA,despite the large amounts consumed,has made study of its degradation necessary.In the paper,single microorganism(P7) and symbiotic culture(P7&B2) capable of degrading PVA have been identified from activated sludge,we present the study on the degradation behavior of PVA by an acclimated PVA-degrading microorganism(P7),and the symbiotic microbial culture (P7&B2) involved.Degradation patterns of PVA by the isolated strains are also discussed.Taxonomic studies and the results of analysis based on 16S rRNA gene sequences revealed that strain P7 belongs to Novosphingobium sp.with 98.2%similarity.While strain B2 was classified as Xanthobacter flavus and showed 100%identities with the 16S rRNA gene of Xanthobacter flavus.As previously reported,extracellular enzyme should coactted with intracellular enzyme in PVA degradation process,and the identified microorganisms needed the addition of enzymes or coenzyme to degrade PVA.However,our experiments displayed that strain P7 could degrade PVA only with the addition of nitrogen source.The PVA degradation rate was 95%,this was an unprecedented find.We also found that strain P7 not only produce extracellular PVA- degrading enzymes to degrade PVA,but also produce intracellular PVA-degrading enzymes for the further utilization of PVA- degrading intermediates.Strain P7 was cultivated in different nitrogen sources,in which organic nitrogen source was more suitable for the microorganism to grow and degrade PVA than inorganic nitrogen source.To identify the symbiotic bacteria with P7 in activated sludge,PVA degradation by the co-culture was examined.Several strains isolated from sludge samples were inoculated into the modified PVA medium(without nitrogen source) with strain P7.In the mixed culture of strain B2 and P7,PVA was degraded completely,the degradation rate was 94.4%.The experiment that PVA- degradability of strain B2 with nitrogen source has also been carried out for a week,and the result showed that strain B2 has no PVA- degrading activity.Strain P7 exhibited a capability of PVA degradation while strain B2 could not utilize PVA as a carbon source.PVA was degraded slowly by a pure culture of strain P7 without the addition of nitrogen source.However,the degradation was markedly enhanced by a mixed culture of P7 and B2.This suggests that the reaction proceeds in the degradation of PVA due to secretion of the nitrogen source by the symbiotic strain.