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The results (Figure 4 and Table 4) showed that the bacteria in this study were mainly Firmicutes (bands 1, 7, 12, and 13), Bacteroidetes (bands 3 and 4), and Proteobacteria (bands 5, 6, 8 and 11), which is consistent with a full-scale anaerobic digester feeding with swine manure in Japan (Niu et al. 2015). The bacterial community structure in the AnMBR differed from the CSTR, and two members belonging to Bacteroidetes (band 3 and 4) that existed in the AnMBR were absent in the CSTR. Considering the short generation time of these two bacteria, the difference was not caused by longer SRT in the AnMBR than the CSTR. Sequencing results (Table 4) showed that bands 3 and 4 were closely related (99% similarity) to Bacteroides propionicifaciens and Bacteroides graminisolvens respectively. The former species produces propionic acids by decomposing saccharides (Ueki et al. 2008), while the latter mainly decomposes macromolecular polysaccharides such as xylan and starch (Nishiyama et al. 2009). A likely explanation for the presence of the additional Bacteroides species in the AnMBR is that interception of the microorganisms by the membrane module increased their contact time with the similar intercepted macromolecules and thereby supported macromolecular digestion by Bacteroides propionicifaciens and Bacteroides graminisolvens and thus their growth and enrichment. In a laboratory-scale continuously running fermentative hydrogen-producing membrane bioreactor, Bacteroides and Clostridium were the dominant genera, with the former predominant genera in the hydrolysis of organics (Shen et al. 2010).
Table 4

Sequences of the of 16S rDNA fragments obtained from DGGE

MicroorganismBandOrganism affiliationIdentify (%)PhylumAccession no.
Bacteria Syntrophomonas palmitatica 99 Firmicutes NR_041528.1 
Bacteroides propionicifaciens 99 Bacteroidetes NR_041485.1 
Bacteroides graminisolvens 99 Bacteroidetes NR_041642.1 
Acinetobacter gyllenbergii 97 Proteobacteria NR_042026.1 
Acidovorax delafieldii 97 Proteobacteria NR_028714.1 
Carnobacterium divergens 96 Firmicutes NR_044706.1 
Psychrobacter frigidicola 99 Proteobacteria NR_042222.1 
11 Pseudomonas kilonensis 99 Proteobacteria NR_028929.1 
12 Syntrophomonas curvata 99 Firmicutes NR_025752.1 
13 Clostridium populeti 98 Firmicutes NR_026103.1 
Archaebacteria Methanobacterium palustre 100 Euryarchaeota NR_041713.1 
Methanosaeta thermophila 100 Euryarchaeota NR_028157.1 
10 Methanoculleus marisnigri 99 Euryarchaeota NR_044723.1 
14 Methanosaeta concilii 99 Euryarchaeota NR_028242.1 
MicroorganismBandOrganism affiliationIdentify (%)PhylumAccession no.
Bacteria Syntrophomonas palmitatica 99 Firmicutes NR_041528.1 
Bacteroides propionicifaciens 99 Bacteroidetes NR_041485.1 
Bacteroides graminisolvens 99 Bacteroidetes NR_041642.1 
Acinetobacter gyllenbergii 97 Proteobacteria NR_042026.1 
Acidovorax delafieldii 97 Proteobacteria NR_028714.1 
Carnobacterium divergens 96 Firmicutes NR_044706.1 
Psychrobacter frigidicola 99 Proteobacteria NR_042222.1 
11 Pseudomonas kilonensis 99 Proteobacteria NR_028929.1 
12 Syntrophomonas curvata 99 Firmicutes NR_025752.1 
13 Clostridium populeti 98 Firmicutes NR_026103.1 
Archaebacteria Methanobacterium palustre 100 Euryarchaeota NR_041713.1 
Methanosaeta thermophila 100 Euryarchaeota NR_028157.1 
10 Methanoculleus marisnigri 99 Euryarchaeota NR_044723.1 
14 Methanosaeta concilii 99 Euryarchaeota NR_028242.1 
Figure 4

Comparison of the bacterial community structure in the CSTR and AnMBR.

Figure 4

Comparison of the bacterial community structure in the CSTR and AnMBR.

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