Construction, Degradation Characteristics And Microbial Community Of The Microbial Consortium FWD1 With High Degradation Efficiency For Wheat Straw

Crop straw is multipurpose renewable biomass resources, decomposition of lignocelluloses by cooperative microbial actions is the effective way to recycle. At present, there were many studies about the lignocellulose degradation bacteria, however, some problems, such as the simple component of enzyme system and the low degradation rate were still existed. Restrictive cultivation method was used to construct the microbial community which has the high ability of lignocellulose degradation by cooperative microbial actions.In this study, nine soil samples were collected from the QingLing Mountains, of which the fir forest soil(QLI) was selected as the next experimental target by considerating the CMCase activity, xylanase activity and degradation efficiency on wheat straw comprehensively. The restricted and successive cultivation method was employed to construct a structurally stable microbial consortium FWD1 by using wheat stalk as the carbon source and the fir forest soil sample as inocula, which colonized by bacteria of higher capability on degradation of lignocellulose. The main contents and results are as follows:1. Construction of a microbial consortium FWD1 with efficient and stability wheat straw degradation bacteriaNine soil samples from from Qinling Mountains were collected. CMCase and xylanase activity on 0 d, 4 d, 8 d, 12 d, 16 d and the weight loss of wheat straw during 16 days of incubation were determined subsequently. The result showed that the fir forest soil sample had the highest CMCase activity and straw decomposition. The consortium(FWD1) was obtained using wheat straw as carbon source and the fir forest soil sample as inocula by the successive cultivation method. wheat straw decomposition ability changes of different generations showed that from 9 generation culture, the rate of wheat straw weight loss were all at about 70%, not much different between each other. PCR- DGGE results also indacted that from 9 generation culture, microbial community composition was stable, the main bacteria stripe and location without too big change, thus a microbial consortium FWD1 with efficient and stability wheat straw degradation bacteria was obtained, with a decomposition rate of 72.92% during 10 days of incubation.2. Decomposition characteristics of the microbial consortium FWD1Compared to the other three groups microbial consortium A, B, C, microbial consortium FWD1 had the highest CMCase activity(79.64U/ml), filter paper enzyme activity(75.74U/ml), xylanase activity(1100 U) and straw decomposition rate(75.22%) at the end of 10-day incubation period. The metabolites products of FWD1 degrading wheat straw were found mainly to be acetic acid, propionic acid, butyric acid and ethanol which were determinated by Gas chromatography. The concentration of acetic acid decreased after increased and then increased. Acetic acid concentration was 140.14 mg·L-1 on the 1st day fermentation and came up to the MAX 655.54 on the 3rd day. Propionic acid, butyric acid and ethanol reached the highest level 18.87 mg.L-1, 127.17, 27.47 on the 1st, 3rd, 7th day, respectively. In addition, FWD1 can also degrade corn stalk, filter paper and absorbent cotton, the degradation rate were 52.34%, 10% and 2.47% within 7 days incubation respectively. PCR-DGGE analysis indicated that each lane had some public bands which the lightness were different and special bands during the decomposition process of wheat straw, corn stover, filter paper and absorbent cotton by FWD1. In addition, Shannon index and richness index of each sample were all increased first and then decreased in whole with the extension of incubation time.3. Microbial community of the microbial consortium FWD1The bacterial compositions of FWD1 and the fir forest soil sample where FWD1 colonized were characterized by using the next generation of high-throughput 16 SrRNA gene sequencing technology. The results indicated that the dominated phyla of FWD1 were Proteobacteria(67.41%), Firmicutes(19.25%) and Bacteroidetes(13.34%) and the predominated species of FWD1 were Clostridium sp. BNL1100(11.80%), uncultured Alcaligenes sp.( 10.30%), uncultured Alcaligenaceae bacterium(6.70%) and Brevundimonas diminuta(3.60%). Successive subcultivation led to enrichment of specific bacterial groups, in phyla Proteobacteria and Firmicutes, particularly in species Clostridium sp.BNL1100 of cellulolytic bacteria which rose to 11.80% from 0.01%.