Mechanism Of Lactic Acid Catabolism By Lactate-Utilizing Bacteria And Its Regulation On Rumen Acidosis

Previous studies indicated that overfeeding large amounts of fermentable carbohydrates is associated with rumen acidosis while the abundances of cellulolytic bacteria decreased and the proportions of starch fermenting and lactic acid producing bacteria increased.The aim of the present experiment was to investigate metabolic mechanism and regulation of lactate-utilizing bacteria that associated with lactate metabolism in rumen of goats in purpose to provide reference for the regulation of rumen acidosis.Trial 1.Study on the role of pH(6.5 and 5.5)in regulating M.elsdeni and S.ruminantium lactate degradation.M.elsdenii and S.ruminantium were grown on sodium L-lactate medium at pH 5.5 and 6.5,respectively.The results showed as follows:1)In the case of pH were 6.5 in culture medium,M.elsdeni mainly produced acetate,followed by propionate and butyrate,while M.elsdeni mainly produced propionate at pH 5.5,followed by acetate and butyrate.In the case of pH were 6.5 or 5.5,S.ruminantium mainly produced propionate,followed by acetic acid.2)The concentration of lactate at pH 6.5 was greater than that at pH 5.5(P<0.05)in M.elsdeni group.The concentration of lactate at pH 5.5 was greater than that at pH 6.5(P<0.05)in S.ruminantium group.3)The activity of D-iLDH and ACK at pH 6.5 were greater than those at pH 5.5(P<0.05)in M elsdeni group.In S.ruminantium treatment,the activity of D-iLDH at pH 6.5 was greater than those at pH 5.5(P<0.05),but the activity of ACK at pH 6.5 was lower than those at pH 5.5(P<0.05).The pH did not change the activity of LR.4)The genes that encoding key enzymes in lactate metabolism were all expressed significantly due to changes in pH(P<0.05).Taken together,our findings provide that the utilization mechanism of lactate in M.elsdenii and S.ruminantium was regulated at the transcription level in response to pH.Trial 2.Study on the role of pH(6.5 and 5.5)in regulating co-culture of M.elsdeni and J.ruminantium lactate degradation.M.elsdenii and S.ruminantium were co-cultured on sodium L-lactate medium at pH 5.5 and 6.5.The results showed as follows:1)In the case of pH were 6.5 in the culture medium,co-culture bacteria mainly produced propionate,followed with acetate and butyrate.2)The proportion of propionate via the acrylate pathway at pH 5.5 was greater than those at pH 6.5.The proportion of propionate via the succinate pathway at pH 6.5 was greater than those at pH 5.5(P<0.05).The percentage of lactate fermented to butyrate at pH 6.5 was higher than those at pH 5.5(P<0.05).The participation of M.elsdenii to lactate fermentation at pH 6.5 was greater than those at pH 5.5 of culture(P<0.05).The participation of S.ruminantium to lactate fermentation at pH 5.5 was greater than those at pH 6.5(P<0.05).3)In M.elsdenii,the relative expressions of ACA at pH 6.5 was greater than those at pH 5.5(P<0.05)but no significant differences were observed in the relative expressions of PAC and ACK(P>0.05).In S.ruminantium,the relative expressions of MD at pH 6.5 was greater than those at pH 5.5(P<0.05)while the relative expressions of LDH at pH 6.5 was lower than those at pH 5.5(P<0.05),but no significant differences were observed in the relative expressions of AP(P>0.05).Taken together,our findings indicate that environmental pH can change the participation of M.elsdenii and S.ruminantium to lactate fermentation at the at the transcription level.Trial 3.Study on the regulation of M.elsdeni and S.ruminantium on rumen acidosis in vitro.To clarify rumen bacterial competition and fermentation pattern shift in rumen acidosis,the rumen acidosis model was established in vitro and the two main lactate-utilizing bacteria(M.and S.ruminantium)were inoculated into the rumen fluid in vitro by adding separately or mixed.The results showed as follows:1)The pH of all inoculation treatments were significantly greater than that of the control(P<0.05).2)The molar proportion of acetate in M and M+S treatments were greater than CON and S treatment(P<0.05).The proportion of propionate in the M treatment was significantly greater than CON group at 6 h and 9 h(P<0.05).After 6 h of fermentation,the proportion of isobutyrate in each inoculation treatments were significantly different(P<0.05),and M treatment has the greatest the proportion of isobutyrate.The proportion of butyrate in M treatment was significantly greater than other treatments(P<0.05).3)All inoculation treatments presented with marked decreases in the concentrations of lactate compared that with control(P<0.05).4)Compared with CON treatment,all inoculation treatments increased the concentrations of NH3-N at 3 h but decreased the concentrations of NH3-N at 6 h(P<0.05).5)All inoculation treatments decreased the concentrations of LPS at 6 h compared with CON(P<0.05).6)The population of S.bovis in M and M+S treatments were significantly lower than CON and the population of B.fibrisolvens、L.fibrisolvens and M.elsdenii were significantly greater than CON and S treatment(P<0.05).The population of S.ruminantium in S and M+S treatments were significantly greater than CON(P<0.05).Taken together,our findings indicate that inoculation of lactate-utilizing bacteria can alleviate rumen acidosis induced by high grain diet in goats.