Effect Of Initial PH Of In Vitro Fermentation On Fiber Degradation And Rumen Microbial Adhesion

This study investigated the effects of the initial pH of fermentation broth on substrate fiber degradation and the adhesion of microbes in the rumen.In vitro fermentation test was used to construct artificial rumen fermentation broth with pH values of high pH(HpH),medium pH(MpH)and low pH(LpH)by adjusting the pH of the initial fermentation broth to study the degradation of substrate fibers and nutrients and the adhesion of rumen microorganisms.To explore the mechanism of the influence of the pH value of the fermentation broth on the degradation of the substrate fiber and the adhesion of microorganisms.The whole experiment was carried out in three parts.Test one.In vitro fermentation experiments were conducted to study the effect of fermentation liquid pH on rumen volatile fatty acid(VFA),ammoniacal nitrogen,substrate crude protein and microbial protein content,as well as the degradation rate of dry matter(DM),neutral detergent fiber(NDF)and acid detergent fiber(ADF).The results show that ruminants themselves have a certain ability to adjust the pH of the initial fermentation broth.As the pH of the initial fermentation broth decreases,the degradation rate of substrate DM,NDF and ADF decreases(P<0.001),and the content of total VFA,propionic acid and isobutyric acid decreases significantly(P<0.01).While the content of ammonia nitrogen,butyric acid,valeric acid and the ratio of acetic acid/propionic acid increased significantly(P<0.05).This shows that lowering the pH of the fermentation broth would affect the composition of VFA and the yield of ammonia nitrogen,and inhibit the degradation of substrate fiber and nutrients.Test two.In vitro fermentation experiments were conducted to explore the effects of initial fermentation pH on rumen microbial interface characteristics and electrochemical indicators,as well as the number and relative abundance of rumen microbes.The results showed that the pH of the fermentation broth had no significant effect on the hydrophobicity of the cell membrane surface and the microbial electrochemical indicators(P>0.05).It had no significant effect on the total bacteria,Prevotella ruminicola,liquid Rumenococcus,Selenomonas ruminantium and Ruminobacter amylophilus(P>0.05).The permeability of the microbial cell membrane decreased first and then increased with the pH of the initial fermentation broth.The surface tension of the fermentation broth decreased significantly with the pH of the initial fermentation broth(P<0.05).Decreasing the pH of the initial fermentation broth will significantly(P<0.05)reduce the adhesion of Fungi,Methanogens,Rumenococcus,Selenomonas ruminantium and Ruminobacter amylophilus.High-throughput sequencing results showed that the pH of the initial fermentation broth only had a significant impact on the Shannon index of solid-phase microorganisms(P>0.05).According to the LEf Se analysis,the bacteria in the p＿Firmicutes,c＿Clostridiales,c＿Negativicutes and c＿Bacilli and their sub-classification levels play an important role in the LpH group;p＿Bacteroidetes,c＿Bacteroidia and o＿Bacteroidales and other bacterial groups play a major role in each classification level of the MpH group;p＿Proteobacteria and its c＿Gammaproteobacteria and o＿Pseudomonadales and other flora have significant effects in the HpH group.The results show that changing the pH of the initial fermentation broth will not affect the stability of the microbial system,but will increase the permeability of the cell membrane and decrease the surface tension,affect the growth,reproduction and adhesion of microorganisms,and then affect the degradation of substrate nutrients and fibers.Test three.In vitro fermentation experiments were conducted to explore the effect of initial fermentation broth pH on rumen solid-phase microbial cellulose binding proteins(CBPs).The results showed that the pH of the initial fermentation broth and the fermentation time had a significant effect on the content of solid-phase CBPs(P<0.05).With the extension of fermentation time,the content of CBPs in each group decreased,which indicated that the amount and ability of microbial adhesion decreased with the extension of fermentation time.Reducing the pH of fermentation broth can significantly reduce the content of CBPs,and increasing the pH of initial fermentation broth can also reduce the content of CBPs,but the effect is less than reducing the pH,which indicates that the initial pH of fermentation broth can affect the adhesion ability of microorganisms by affecting the content of CBPs,but the effect of increasing the pH of fermentation broth on the adhesion ability of microorganisms is less than reducing the pH of fermentation broth.In summary,the lowering pH of fermentation broth can affect the growth and reproduction of rumen microorganisms and their adhesion to substrate fibers and the amount of adhesion by affecting the surface tension of the rumen fermentation broth,the physical and chemical properties of the microbial interface,and the content of rumen microbial CBPs.The degradation rate of the fermentation substrate fiber and nutrients is reduced.