Screening Of Polyvinyl Alcohol-degrading Fungi And The Mechanism Of The Degradation Process

Polyvinyl alcohol(PVA)is a biodegradable polymer material with good film strength,adhesion,chemical stability and other excellent mechanical properties.It is widely used in textile,paper-making,chemical industry and other fields,however,it has long degradation cycle and poor biodegradability.In order to solve the environmental pollution problem caused by the use of polymer materials,more and more researchers began to focus on the screening and isolation of PVA-degrading microorganisms,as well as genetic modification of degradable microorganisms,in order to improve the degradation efficiency of polymer materials.At present,most of the microorganisms found to degrade PVA are bacteria(such as Pseudomonas sp.and Bacillus sp.),but there is little research on fungi.In this experiment,the fungal community structure of polyvinyl formal(PVFM)materials during composting was analyzed by high-throughput sequencing.The fungi which could effectively degrade PVA were screened out from the degraded polyvinyl alcohol.The degradation characteristics of PVA1788/99 and PVA2488 in the degradation process of single strain were compared,and the difference between them was analyzed by gel permeation chromatography(GPC)and Fourier transform infrared spectroscopy(FTIR).The molecular weight and functional groups of PVA were measured to explore the degradation mechanism of PVA.The main contents and results of this paper are as follows:1.Through high-throughput sequencing,83244?73555 sequences were obtained from the PVA foam which have degraded for 1 year(1Y)and 2 years(2Y),separately.And the total OTU of 1Y and 2Y sample was 2963 ? 2926,respectively.The Alpha diversity analysis revealed that the diversity of microorganisms increased with the prolongation of degradation time.2.At the level of phyla,the dominant community in the 1 year degraded sample was Ascomycota,the relative abundances is 69.83%,and the dominant community in the 2 year degraded sample were Ascomycota,Zygomycota,the relative abundances are 31%,19.3%.At the level of genus,the dominant community in the 1 year degraded sample was Galactomyces(49.86%),and the dominant community in the 2 year degraded sample were Mortierella(19.05%)and Pseudogymnoascus(18.98%).it indicated that the structure and community ofthe dominant degrading fungus have changed significantly with the change of degradation time.However,both Galactomyces and Pseuudogymnoascus belong to Ascomycota,indicating that Ascomycota fungi have great potential for biodegradation of polyvinyl alcohol materials.3.Three strains of polyvinyl alcohol degrading bacteria were isolated from the surface of degradable materials,and they were identified as Eutypella sp.BJ,Aspergillus sp.12 B and Dirkmeia sp.M19 through morphological observation and ITS4/5 sequence analysis,among which Eutypella sp.BJ and Aspergillus sp.12 B belong to Ascomycota.4.During the degradation cycle,the degradation rates of strains Eutypella sp.BJ and Aspergillus sp.12 B to PVA1788 were 87.4% and 80.9%,respectively,to PVA1799 86.31%and 79.89%,and to PVA2488 reached 44.8%,41.1% separately.It indicated that the lower degree of polymerization was beneficial to microbial degradation,while for PVA 1799 and PVA 1788 materials with the same degree of polymerization and similar degree of alcoholysis,the effect of two fungi on the degradation was not significant.5.In the experiment of biodegradation of polyvinyl alcohol materials,it was found that under the action of strain Eutypella sp.BJ,the average molecular weight of PVA1799 decreased from 71387 to 24238.3;under the action of strain Aspergillus sp.12 B,the average molecular weight of PVA1799 also decreased from 71387 to 38419.The results showed that both fungi had good degradation effect on polyvinyl alcohol,and Eutypella sp.BJ had better degradation effect than Aspergillus sp.12 B.In addition,some carboxylic acids are produced as the molecular weight of biodegradable polymers decreases.