Functional characteristics and diversity of a novel lignocelluloses degrading composite microbial system with high xylanase activity.

To obtain an efficient natural lignocellulolytic complex enzyme, we screened an efficient lignocellulose degrading composite microbial system (XDC-2) from composted agricultural and animal wastes amended soil following a long-term directed acclimation. The XDC-2 could not only degrade natural lignocelluloses, but could also secret extracellular xylanase efficiently in liquid culture under static conditions at room temperature. The XDC-2 degraded rice straw by 60.3% after fermentation for 15 days. Hemicelluloses were decomposed effectively, while the extracellular xylanase activity was dominant with an activity of 8.357 U ml-1 on day 6 of the fermentation period. The extracellular crude enzyme noticeably hydrolyzed natural lignocelluloses. The optimum temperature and pH for the xylanase activity were 40 degrees and 6.0. However, the xylanase was activated in a wide pH range of 3.0-10.0, and retained more than 80% of its activity at 25-35 degrees and pH 5.0-8.0 after three days of incubation in liquid culture under static conditions. PCR-DGGE analysis of successive subculture indicated that the XDC-2 was structurally stable over long-term restricted and directed cultivation. Analysis of 16S rRNA gene clone library showed that the XDC-2 was mainly composed of mesophilic bacteria related to the genera Clostridium, Bacteroides, Alcaligenes, Pseudomonas, etc. Our results offer a new approach to exploring efficient lignocellulolytic enzymes by constructing a high-performance composite microbial system with synergistic complex enzymes.