Effect of deleting acetic acid-producing key enzyme gene of Selenomonas ruminantium on the ruminal fermentation in vitro

Abstract

The aims of this study were to examine the effects of the engineering bacteria TnK6 (The deleting acetic acid-producing key enzyme gene of Selenomonas ruminantium) on ruminal fermentation in vitro. The mixed culture of ruminal bacteria (ruminal fluids from the healthy sheep), buffer, and primarily degradable substrates were inoculated with equal number of S. ruminantium K6 and its engineering bacteria TnK6, respectively. The pH, the concentration of volatile fatty acids (VFA; acetic acid, propionic acid, and butyric acid) and lactic acid in the mixed culture were detected at 0, 2, 4, 6, 8, 10, 12, 24, 36, and 48 h of incubation. The results showed that the concentrations of lactic acid in the rumen fluid cultured with TnK6 were decreased. Although, the concentrations of propanoic acid in TnK6 were not higher than that in K6 at the same time, the ratio of acetic acid to propionic acid was decreased significantly. The results indicated that TnK6 could use lactic acid and improve the portion of propionic acid in the rumen fluids. To the best of our knowledge, this is the first report that the engineering bacteria can regulate the fermentation of ruminal microorganisms in vitro. This research contributes to develop a new method to regulate the rumen fermentation. Key words: Rumen, Selenomonas ruminantium, gene deletion, fermentation, in vitro.