Microbial load, physical properties and molecular assessment of microbial community structure in rapid composting system

The predominant microbial communities involved in rapid composing system (RCS) were determined using terminal-restriction Fragment Length Polymorphism (T-RFLP) coupled with Denaturing Gradient Electrophoresis (DGGE) to further understand the role of microbial community structures in RCS. The RCS treats organic residues by batch in compost bins for 11-14 d and operates in a self-induced heat generation, creating an initial mesophilic stage (45 deg C) and subsequent thermophilic stage (62 deg C). Population level of the final product was 5.68 x 10 sup 5 cfu/g dry samples and 2.26 x 10 sup 6 cfu/g dry samples at 37 deg C or 50 deg C incubation, respectively. The pH values during the operation did not vary significantly (pH 7.3-7.9), while moisture content was reduced from 17% to 3.5% T-RFLP analysis of the samples during degradation exhibited two major ribotypes (T-rfs), 167.4 and 162.6 which relative population level of 49.6% (early stage) and 64.3% (final product), respectively. DGGE and 16S rDNA analysis revealed that the system consisted of the following genera : Lactococcus sp., Bacillus sp. Geobacillus or Aeribacillus sp. Corynebacterium sp or Amycolatopsis sp., Saccharopolyspora sp. and Staphylococcus sp. The strain Lactococcus sp. was found in early stages, while Bacillus sp.Corynebacterium sp. and/or Amycolatopsis seemed to predominate during the early and subsequent periods, respectively. Staphylococcus sp. and Saccharopolyspora sp. only existed at the last stage of composing period. The two major ribotypes in T-RFLP analysis and two major bands on DGGE analysis seemingly followed similar population patterns. DGGE revealed that though the samples analyzed came from different batches, results showed that the microbial population fingerprints were well represented and were simultaneously detected in the different batches of samples. This result could indicate that a preparation of composite microflora from each composting stage could be developed and used as a seeding materials for improved composting process.