succinogenes S85 The 16S rRNA gene copy numbers for these strain

succinogenes S85. The 16S rRNA gene copy numbers for these strains at 96 h of incubation were significantly higher (P < 0.05) in triculture than in monocultures and two-member coculture (Fig. 2a). Scanning electron microscopy (SEM) observations showed that all three strains attached to rice straw in monoculture (Fig. 2b, i–iii). In the triculture, the

three strains were shown to ABT199 be closely located on the rice straw (Fig. 2b, iv). Although the positive interaction between rumen bacteria has been reported in the previous studies, the present result is the first demonstration of synergism between the newly cultured group U2 bacterium R-25 and F. succinogenes. The extent of increase in DM digestion by coculture of strain R-25 and F. succinogenes S85 was comparable with the previous coculture studies using the combinations of F. succinogenes and several nonfibrolytic species, where DM digestion was enhanced in coculture at 1.05–1.18-fold (Dehority & Scott, 1967; Kudo et al., 1987; Osborne & Dehority, 1989; Fondevila & Dehority,

1996; Sawanon et al., 2011). Growth and fermentation patterns of F. succinogenes S85 were altered in coculture with strain R-25. Higher level of 16S rRNA gene copy number (at 96 h) and succinate production (at 48 h) of F. succinogenes S85 suggest that strain R-25 had a positive effect on fermentation activity of F. succinogenes S85. Enzyme activity in coculture of strain R-25 with F. succinogenes S85 partly supports this suggestion. Although extracellular activity of CMCase and xylanase was significantly higher in coculture of strains R-25 and F. succinogenes S85, activity of extracellular CMCase and xylanase from strain R-25

alone was almost negligible. Therefore, elevated extracellular activity of fibrolytic enzyme in the coculture is likely to be solely attributable to F. succinogenes S85. Possible explanations Ribonucleotide reductase of this positive alteration of F. succinogenes S85 activity by strain R-25 include the consumption of oligosaccharides and hydrogen, which can accumulate in the monoculture. Previous research has shown that endoglucanase activity of F. succinogenes S85 is repressed by cellobiose (McGavin et al., 1990). Furthermore, the consumption of hydrogen by methanogenic archaea leading to increased ATP production and/or organic acid concentration of fibrolytic strains has been reported as interspecies hydrogen transfer (Latham & Wolin, 1977; Williams et al., 1994; Rychlik & May, 2000). Consumption of oligosaccharides and hydrogen to produce lactate by strain R-25 could lead to the maintenance of the fibrolytic activity of F. succinogenes S85, resulting in enhanced DM digestion in coculture.

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