Research On Lignin Degradation And Its Microbial Characteristics During Composting Of Agricultural Wastes

Since lignin is the major organic compound that limiting composting speed, its degradation is essential for the operation of composting. Lignin biodegradation and its microbial characteristics during composting of agricultural wastes were studied. Firstly, traditional method, Biolog assay, PLFA analysis and quinone profiles were used respectively to investigate the microbial community succession with lignin degrading potential. Secondly, dominant and effectively lignin degrading microorganisms were screened. Nonwhite-rot fungi, Penicillium simplicissimum and Aspergillus niger, were found to be important in lignin degradation. Their degrading characteristics and mechanisms were also studied. Finally, effect of lignin biodegradation on humification by Streptomyces badius isolated from maturation phase was investigated.The results obtained through the traditional method indicated that lignin was mainly degraded during the thermophilic phase and maturation phase of composting. Polyphenol oxidase (PPO) and peroxidase (POD), especially PPO was found to be the most important catalyzer in lignin degradation. Bacteria, fungi and actinomycetes with lignin degrading ability changed greatly during every compost phase. Actinomycetes were found to be the most effective microorganism to degrade lignin followed by fungi and bacteria.Since bacterial communities played important synergic function in lignin degradation, they were analyzed using Biolog method in agricultural waste composting. The results of cluster analysis and principle component analysis indicated that bacterial communities varied greatly during the first stage of composting, while began to stabilize during the second stage. Bacteria that could utilize the first, second and fourth kinds of carbon sources on Biolog GN2 plate were found to be able to degrade lignocellulose. Thereinto, the first and second kinds of carbon sources were the dominant ones during composting, while the bacteria that metabolize the fourth kind of carbon sources were believed to be thermophilic ones.Phospholipid fatty acid (PLFA) and Partial Least- squares Regression (PLS) methods were selected to establish the quantitative regressive model between lignin content and PLFA. Through the analysis of model parameters, it was found that a few microorganisms with strong lignin degrading ability and plentiful microbes with weak lignin degrading ability cooperated during the composting of agricultural wastes. The former were fungi and actinomycetes that dominant in lignin degradation, while the latter was bacteria. Microbial species were believed to be more important than amounts. During the thermophilic phase, the effective lignin degrading microbial proportion was 42:35:6:17 (Gram-positive bacteria: Gram-negative bacteria: actinomycetes: fungi), while the proportion was 58:23:4:15 during the maturation phase of composting. The microbial content was about 108cells/g dw.The changes of microbial community during agricultural waste composting were successfully studied by quinone profiles. Mesophilic bacteria indicated by MK-7 and mesophilic fungi containing Q-9 as major quinone were predominant and seemed to be important during the initial stage of composting. Actinobacteria indicated by a series of partially saturated and long-chain menaquinones were preponderant during the thermophilic period. While actinomycetes, fungi and some bacteria, especially those microbes containing MK-7(H4) found in Gram-positive bacteria with a low G+C content or actinomycetes were found cooperate during the latter maturating period. Since lignocellulsoe is abundant in the agricultural wastes and its degradation is essential for the operation of composting, it's important to establish the correlation between the quinone profiles changes and lignocellulose degradation. The microbes containing Q-9 or Q-10(H2) as major quinone were found to be the most important hemicellulose and cellulose degrading microorganisms during composting. While the microorganisms containing Q-9(H2) as major quinone and many thermophilic actinomycetes were believed to be responsible for lignin degradation during agricultural waste composting.Several strains include Aspergillus niger F4-1, Aspergillus oryzae F1-4, Penicillium simplicissimum F1-1, Streptomyces badiusA4-2 and thermophilic actinomycetes Thermoactinomyces sp.A2-2 that have strong lignin degrading ability were obtained through the screening experiments. A. niger was capable of utilizing phenolic and nonphenolic lignin model compounds. Lignin peroxidase (LiP), Manganses peroxidase (MnP), Laccase were believed to be the most important catalyzes in biodegrading process. P. simplicissimum was capable of utilizing several lignin model compounds, making aromatic dyes decolourise and degrading natural lignin. All these results proved that P. simplicissimum has ligninolytic ability. Laccase was the most important catalyzes in the biodegrading process. Different from the degrading mechanism of the white-rot fungi, the lignin degradation by P.simplicissimum mainly happened during the primary metabolism and it was greatly influenced by the pH of media, the concentration of Cu2+ and Mn2+.The laccase activities of P. simplicissimum during solid state fermentation with rice straw were studied. And the degradation of lignocellulose was also determined. Results show that all supplemental carbon sources inhibited the laccase activity in different degrees. While proper concentration of supplemental nitrogen sources remarkably enhanced the laccase activity. The enhancement of laccase activity by ordinary laccase inducers 2, 2'-azino-bis (3-ethylbenzthiazoline- 6-sulfonic acid) and xylidine was not observed in this study. Lignocellulose degradation was improved when laccase activity was relatively low during prophase of fermentation, which proved the polymerizing function of laccase in lignin degradation by P. simplicissimum. Some metabolites may act as mediators to help lignin degradation during the fermentation anaphase. All supplemental sources may induce the peak of Lac activity on day 3 when the polymerizing function was especially strong.The effect of lignin biodegradation on humification by Phanerochaete chrysosporium and S. badius were compared. The results indicate that lignin degrading microorganisms could promote humus formation. Since the degrading mechanisms of two strains were different, the approaches of humus formation from lignin with P. chrysosporium and S. badius were also different. P. chrysosporium metabolize lignin to simple molecules (FA), which then were polymerized to complex molecules (HA). While S. badius modified lignin to HA, which then were transformed to FA.