[Degradation of lignocellulose in the corn straw by Bacillus amyloliquefaciens MN-8]

Microbial degradation of lignocellulose is one of the key problems that need to be solved urgently in the process of utilizing biomass resource. Bacillus amyloliquefaciens MN-8 is our previously isolated bacterium capable of degrading lignin. To determine the capability of strain MN-8 to degrade lignocellulose of corn straw, B. amyloliquefaciens MN-8 was inoculated and fermented with solid-state corn straw powder-MSM culture medium. The changes in the enzyme activity and degradation products of lignocellulose were monitored in the process of fermentation using the FTIR and GC/MS. The results showed that B. amyloliquefaciens MN-8 could produce lignin peroxidase, manganese peroxidase, cellulase and hemicellulase enzymes. The activities of all these enzymes reached the peak after being incubated for 10-16 days, and the highest enzyme activities were 55.0, 16.7, 45.4 and 60.5 U · g(-1), respectively. After 24 d of incubation, the degradation percentages of lignin, cellulose and hemicellulose were up to 42.9%, 40.6% and 27.1%, respectively. The spectroscopic data by FTIR indicated that the intensities of characteristic absorption peaks of lignin, cellulose and hemicellulose of the corn straw were decreased, indicating that the lignocellulose was degraded partly after being fermented by B. amyloliquefaciens MN-8. GC/MS analysis also demonstrated that strain MN-8 could degrade lignocellulose efficiently. It could depolymerize lignin into some monomeric compounds with retention of phenylpropane structure unit, such as amphetamine, benzene acetone and benzene propanoic acids, by the rupture of β-O-4 bond connected between lignin monomer, and it further oxidized some monomer compounds into Cα carbonyl compounds, such as 2-amino-1-benzeneacetone and 4-hydroxy-3,5-dimethoxy-acetophenone. The GC/MS analysis of the degradation products of cellulose and hemicellulose showed that there were not only monosaccharide compounds, such as glucose, mannose and galactose, but also some glycolysis products including formic acid, acetic acid, propionic acid, 1,1-ethanediol and 3-hydroxy butyric acid. Our results demonstrated that B. amyloliquefaciens MN-8 is capable of degrading lignocelluse of the corn straw effectively and the degradation capacity depends on the lignocellulase activity.