The Screening Of Aspergillus-Streptomyces-Pleurotus And Their Coimmoblized Biodegradation Of Alkali Lignin

Lignin, next to cellulose,is the second most abundant compound in plant biomass and by far the most abundant aromatic substance present in the biosphere.Studies on the biodegradation of lignin have significant implications for our understanding of the global carbon cycle and development of an environmentally friendly technique for selective removal of lignin in paper-making.Also the effective bioconversion of lignin is important to fully utilize it for new materials or energy.Most lignin research on bioconversion and biodegradation has been on wood-rot fungi,particularly on white-rot fungi.and not on other lignolytic organisms.However, because of slow growth rates;easily counteracted by other lower microorganisms;damageable enzymes and production costs for them,etc.,the direct use of single white rot fungus and their enzymes in industrial processes is still very difficult now.For that reason, according to micro-ecology principle,the community combined system of actinomyces—fungi was set up. And further a coimmobolized bed reactor was structured, which can be running continuously under non sterilization.One strain of white rot fungus--P. ostreatus G5was selected from6strains of Genus Pleurotus with its high growth rate, degrading alkali lignin and tolerance to lignin. Furthermore, P. ostreatus G5was compared to the typical white rot fungi--P.chrysosprium5.776and T. versicolor5.161. The results show that P. ostreatus G5is a better strain for lignin decomposing.One strain of bacteria was isolated from the lignin degrading reactor. It was identified as one Microbacterium sp.GE1017with its morphologic and high homology to the genus of rDNA sequence. The sequence was registered in the NCBI GenBank Data Library under the accession number FJ405359.Strain GE1017possesses high activity of MnP(2493.3U·L-1) and ability of decomposing lignin (degrading rate about60%).Through screening from forest soil of Dalian, two novel isolated actinomycete strains were identified as Streptomyces spp.strains F-6and F-7by their morphology, cultural characteristics and high homology to the16S rRNA gene.The sequences were registered in the NCBI GenBank Data Library under the accession numbers F-6FJ405358,F-7FJ405357.Both strains possessed laccase and manganese peroxidase activities.Laccase activity produced by strain F-6was up to935.4U·g-1dry cell weights.More than50%of alkali lignin was removed by strains F-6and F-7in12days of incubation. GC-MS analysis of the biodegraded products showed strain F-6converted lignin into phenol and broken phenol compounds.The two strains could co-culture with white rot fungus, and the combined actinonycete-fungus system decomposed alkali lignin effectively.A fungus strain F-3was selected from fungal strains isolated from forest soil in Dalian of China. It was identified as one Aspergillus sp.stain F-3with its morphologic,cultural characteristics and high homology to the genus of ITS rDNA sequence. The sequence was registered in the NCBI GenBank Data Library under the accession number GQ149340.The budges or thickened node-like structures are peculiar structures of hyphae of the strain.The fungus degraded64.8%of alkali lignin (2000mg L-1) after day8of incubation at30℃at pH7. The removal of colority was up to100%at8days. The biodegradation of lignin by Aspergillus sp. F-3favored initial pH7.0. Excess acid or alkali conditions were not propitious to lignin decomposing.Addition of Ammonium L-tartrate or glucose delayed or repressed biodegradation activities.During lignin degradation, manganese peroxidase (28.2U·L-1) and laccase (3.5U·L-1) activities were detected after day7of incubation.GC-MS analysis of biodegraded products showed strain F-3could convert alkali lignin into small molecules or other utilizable products.Strain F-3may co-culture with white rot fungus and decompose alkali lignin effectively(removal ratio56.6%)Four strains of Aspergillus F-3,Streptomyces spp.strains F-6and F-7, P. ostreatus G5were used to deal with coimmobilized biofilm formation on the ceramic ball-packed bed reactor. The start-up was finished in one month. Under non sterilization and the operation conditions of degradation liquor with alkali lignin2000mg L-1,glucose10g L-1,HRT12h, at room temperature,the reactor was continuously running for18months.During the running period, the removal ratios were>70%of alkali lignin,>90%of colourity,>90%of COD. GC-GS analysis of products degraded by the reactor shows lignin can be decompose and convert into aromatic alcohols, aromatic acid esters,phenols,and small molecule alcohols, carboxylic acid compounds.Most of them are aromatic compounds.The reactor can maintain the degrading functions and antimicrobial pollution ability, which implies its potential in industrial use.