Study On The Biodegradation Of Polyvinyl Alcohol By Microorganisms

Polyvinyl alcohol(PVA)is a water-soluble synthetic polymer and an important chemical raw material that has been used in the production industries of polyvinyl alcohol ester,textiles,paper coatings,emulgator and adhesives.In the textile industry,a substantial amount of PVA has been widely used and thus a mass of wastewater arises,which resulted in serious environmental pollution and industrial wastewater that fail to be processed.PVA usually accumulated in the soil and oceans for its stable structure and slow degradation,which become clear that PVA causes adverse effects in all ecosystems and PVA is of particular concern to our health.Therefore,global concerns have been raised regarding a significant environmental problem“how to realize the effective and environment friendly degradation of PVA by microorganisms and set up PVA recycling system”.In this study,two PVA-degrading bacteria were screened from oil sludge using PVA as a sole carbon source in the culture medium.These two bacteria were identified by the 16S rDNA nucleotide sequence alignment,morphological and biochemical characteristics and phylogenetic analysis.The results of the study show that these two bacterial strains were identified and named as Stenotrophomonas sp.SA21and Bacillus cereus RA23.The strain Stenotrophomonas sp.SA21 can degrade 90%of the PVA(1 g/L)present in culture medium after 4 days at p H7.5 and 30?.The effect of nitrogen sources on the production of PVA-degrading enzyme involved in the biodegradation process was significant,and the enzymatic activity reached 82 U/m L when ammonium nitrate or urea was used in the optimized medium.The PVA-degrading strain B.cereus RA23 can degrade 85%of 0.1%PVA after a five-day incubation period under the optimized culture conditions.Interestingly,the inorganic nitrogen source(NH₄Cl)was found to enhance the PVA degradation rate.The p H and temperature of the culture medium also influenced the maximum biodegradation rate of PVA by B.cereus RA23.FTIR analysis showed that these two bacteria can break the important functional groups(carboxylic acid,methyl ester,ketone and aldehyde)in the main chain of PVA polymers,then cause the structural changes,and further trigger the biodegradation of PVA.At the same time,the PVA-degrading genes involved in the pva operon was investigated to identify PVA dehydrogenase gene,PVA oxidized hydrolase gene and cytochrome c gene.Subsequently,the three genes were sequenced,and the amino acid sequences were deduced.Furthermore,the isoelectric point,molecular weight,possible formation secondary structure and three-dimensional structure of three enzymes were also characterized in detail by bioinformatics tools.This study will provide the bacterial resources and theoretical basis for the development of high-efficient PVA-degrading techniques and wastewater treatment technologies.Moreover,the researching results are of great application to accelerate the degradation and recycling of PVA as well as other resources,which is in accordance with the demand of sustainable development.