[Microbial diversity of a community for ensiling rice straw at low temperature and fermentation dynamics]
Yang H, Yuan X, Liu X, Wang X, Cui Z
College of Life Sciences, Northeast Forestry University, Harbin 150040, China.
To accelerate the conversion of rice straw into feeds in the low-temperature region, a microbial community was constructed by continuous enrichment cultivation. Microbial diversity and dynamics during the fermentation at 10 degrees C was analyzed.
The community was selected at 5 degrees C under static condition. To analyze the inoculating effects, the community and commercial inoculant ( CI: composed of Lactobacillus plantarum, Enterococcus faecium, L. salivarilus, Pediococcus acidilactici) were respectively inoculated into the rice straw for 30 d fermentation at 10 degrees C. Fermented products were detected by gas chromatography - mass spectrometry (GC-MS). Composition microorganisms of the community were analyzed using cloning library. Microbial dynamics during the fermentation was detected by denatured gradient gel eletrophoresis (DGGE). Quantitative PCR was used for tracking the composition microorganisms of the community during the fermentation.
The results from 16S rDNA cloning library showed that the community was mainly composed of Lactobacillus spp. and Leuconostoc spp. At 6d fermentation, the pH and the lactic acid bacterial colony forming units (LAB CFUs) in the fermented rice straw with the community amounted to 4.3 and 2.9 x 10(9) CFU/g fresh matter (FM), respectively. The pH and LAB CFUs with the CI were respectively 5.3 and 2.9 x 10(9) CFU/g FM. At 30 d fermentation, the lactic acid concentrations with the community and the CI were respectively 8.1 g/kg FM and 2.0 g/kg FM. From DGGE patterns, both L. sakei and Leuconostoc inhae of the community were detected at 6d fermentation and existed during the fermentation. For the treatment with the CI, the uncultured bacterium was detected at 6d fermentation besides the composition microorganisms of the CI. At 16d and 30d fermentation, only L. plantarum and E. faecium were detected. Quantitative PCR showed DNA mass of L. sakei amounted to 41.0% at 6d fermentation in the treatment with the community. At 16d, DNA mass of L. sakei was 65%. The highest value (5.5%) of DNA mass of Le inhae appeared at 6d of fermentation.
The community could effectively colonize into the rice straw fermentation system and accelerate the fermentation process at low temperature. The dominating microorganism of the community was L. sakei at 10 degrees C.