The Characteristics Of Lignocellulose Degradation In Ovatospora Sp. XJ161 And Its Application

Lignocellulosic biomass is a complex polymer formed by cross-linked chemical bonds among as lignin,cellulose,and hemicellulose,and such heterologous structure forms a natural barrier for microbial decomposition and utilization of lignocellulose.However,there are a group of microorganisms evolved with enzymatic system which can degrade the polysaccharides and lignin for their carbon sources in nature.Plant residues are decomposed under the synergistic action of this group of microorganisms and then are eventually converted to be a part of the soil composition which is known as humic acid in edaphology.However,the degree and preference of lignocellulosic degradation vary greatly among different types of microorganisms.In addition,the growth state of microorganisms is easily affected by the environment,which in turn affects the expression of related enzymes and the capacity to utilize substrates.This study focused on Ovatospora sp.XJ161.Firstly,growth conditions and lignocellulosic degradation were characterized.Then the genome was analyzed to understand the capacity and mechanism of lignocellulosic degradation of the strain.Finally,the differences in carbohydrate-degrading enzymes between this strain and five other types of white rot fungi were compared by comparative genomics analysis.At the same time,the strain was combined with five white rot fungi to treat corn stover and vinegar grain.The potential of the strain in the field of lignocellulose degradation and utilization was evaluated for their ability in producing humic acid.The main research results of this paper are summarized as follows:1.After characterizing the growth of the strain under different culture conditions such as temperature,p H,salt concentration,carbon and nitrogen source and water content,it was found that Ovatospora sp.XJ161 was a heat-resistant and alkali-tolerant filamentous fungus.In addition,Ovatospora sp.XJ161 could use various common sugars as its carbon sources,but the utilization of different carbon sources was affected by nitrogen sources.To further evaluate the capacity in lignocellulosic degradation of the strain,the extracellular lignocellulosic degradation enzyme activities,iron reducing power and the components changes of corn stover during the growth of Ovatospora sp.XJ161 on corn stover were measured.Among them,the total cellulase activity reached the highest value of 2.1 IU/g on the 15^th day fermentation,β-glucosidase activity reached the highest value of 10.3 IU/g on the 21^st day and xylanase activity reached the highest value of 35.5 IU/g on the 30^th day.According to the weight loss rate of each component,the weight loss rate of total cellulose,total hemicellulose and total lignin at 30^th days were 50.4%,57.2%and18.9%,respectively.These results showed that Ovatospora sp.XJ161 had weak lignin degradation ability but efficient cellulose and hemicellulose degradation ability.2.From genome sequencing analysis,a total of 8191 coding genes were predicted from the genome of Ovatospora sp.XJ161 and a total number of 8086 genes with protein function were predicted.Among them,the metabolism of related components such as carbohydrates and polysaccharides was vigorous.The genes related to carbohydrate metabolism were the most,with a total of 287,accounting for 3.50%of all genes in the genome.According to the results of online annotation in the Carbohydrate Active Enzymes Database（CAZyme）,the genome of Ovatospora sp.XJ161 lacked the laccase expression gene,but had one predicted versatile peroxidase gene,two generic peroxidase genes and some lignin-degrading and auxiliary enzymes genes.Glycoside hydrolase family,polysaccharide lyase family,carbohydrate esterase family,some carbohydrate binding modules and AA3-1,AA3-2,AA7,AA9,AA11 in auxiliary activity family（AA）had the ability to degrade cellulose and hemicellulose or auxiliary enzyme activities.These results provided a molecular sight from a genome level to explain why the strain showed weak lignin degradation ability and strong cellulose and hemicellulose degradation ability.3.Using comparative genomic analysis,it was found that Ovatospora sp.XJ161 and five different types of white rot fungi had differences but complementarity in the compositions of carbohydrate degrading enzyme systems.Then combined with the growth difference between Ovatospora sp.XJ161 and white rot fungi,the two were used to treat corn stover and vinegar grain in batches according to different combinations,which proved the advantage of Ovatospora sp.XJ161 in using biomass to produce humic acid.Ovatospora sp.XJ161 showed different capacities in producing humic acid from biomass when combine with different white rot fungi.When it was combined with Bjerkandera adusta DE to treat corn stover,the maximum humic acid content could reach 43.9%after the biomass fermentation by B.adusta DE and followed by Ovatospora sp.XJ161,which was 91.2%higher than that of untreated corn stover.When it was combined with Pleurotus ostreatus BP2 to treat vinegar grain,the maximum humic acid content could reach 66.5%after the biomass fermentation by P.ostreatus BP2 and followed by Ovatospora sp.XJ161,which was 67.6%higher than that of untreated vinegar grain.In summary,the strain Ovatospora sp.XJ161 has the advantages of high temperature resistance and alkali resistance.And it was demonstrated to preferentially degrading cellulose and hemicellulose then lignin under high temperature and dry conditions during biomass fermentation under 60%water content.For the first time in this paper,strain of Ovatospora and white rot fungi were used to converse corn stover and vinegar grain in batches to produce humic acid,which showed its application potential in the development and utilization of lignocellulosic biomass.