Abstract

SANCHEZ-SANTILLAN, Paulino  and  COBOS-PERALTA, M. Antonio. In vitro production of volatile fatty acids by reactivated cellulolytic bacteria and total ruminal bacteria in cellulosic substrate. Agrociencia [online]. 2016, vol.50, n.5, pp.565-574. ISSN 2521-9766.

In vitro methods are suitable for comparing degradation of cellulosic substrates and synthesis of products derived from fermentation, such as volatile fatty acids (VFA). The objectives of this study were to compare the production of VFA of a culture of reactivated cellulolytic bacteria (CBC) with that of total ruminal bacteria (TRB) in cellulosic substrates, and to evaluate the relationship between VFA and in vitro degradation. The culture of cellulolytic bacterial was obtained after four transfers of ruminal fluid to fresh culture media and Whatma paper, and preserved by lyophilization. The inocula were CBC, TRB and one co-culture (50:50) of the two inocula together. The substrates were alfalfa, maize stalks, Bermuda grass and crystalline cellulose. In in vitro degradation, pH, percentage of dry matter (DM) degradation (%DMDEG) and VFA were measured. The experimental design was completely randomized with a 3×4 factorial array; inocula and substrates were factors. The three inocula had heterofermentative activity in the cellulosic substrates. None of the three were different in VFA production (p>0.05) in fermentation of alfalfa, Bermuda grass or maize stalks. However, CBC produced more acetate (p≤0.05) than the TRB in fermentation of alfalfa and Bermuda grass. CBC exhibited synergism in the production of acetate with TRB in crystalline cellulose since the co-culture produced more acetate than TRB (p≤0.05). The co-culture and TRB were not different (p>0.05) in %DMDEG in Bermuda grass, maize stalks and crystalline cellulose. Under these conditions, the culture of reactivated cellulolytic bacteria exhibits heterofermentative activity in cellulosic substrates, and acetate is the main product of fermentation. These bacteria, however, do not improve DM degradation when co-cultured (50:50) with total ruminal bacteria.

Keywords : Acetate; in vitro fermentation; in vitro degradation; cellulose; bacteria.

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