Megasphaera elsdenii Lactate Degradation Pattern Shifts in Rumen Acidosis Models.

Yizhao Shen,Fangfang Zhao,Mengzhi Wang,Jingyuan Fu,Luoyang Ding,Lianmin Chen,Chao Wang,Hongrong Wang

doi:10.3389/fmicb.2019.00162

Abstract

Background: Megasphaera elsdenii is an ecologically important rumen bacterium that metabolizes lactate and relieves rumen acidosis (RA) induced by a high-grain-diet. Understanding the regulatory mechanisms of the lactate metabolism of this species in RA conditions might contribute to developing dietary strategies to alleviate RA.Methods: Megasphaera elsdenii was co-cultured with four lactate producers (Streptococcus bovis, Lactobacilli fermentum, Butyrivibrio fibrisolvens, and Selenomonas ruminantium) and a series of substrate starch doses (1, 3, and 9 g/L) were used to induce one normal and two RA models (subacute rumen acidosis, SARA and acute rumen acidosis, ARA) under batch conditions. The associations between bacterial competition and the shift of organic acids’ (OA) accumulation patterns in both statics and dynamics manners were investigated in RA models. Furthermore, we examined the effects of substrate lactate concentration and pH on Megasphaera elsdenii’s lactate degradation pattern and genes related to the lactate utilizing pathways in the continuous culture.Results and Conclusion: The positive growth of M. elsdenii and B. fibrisolvens caused OA accumulation in the SARA model to shift from lactate to butyrate and resulted in pH recovery. Furthermore, both the quantities of substrate lactate and pH had remarkable effects on M. elsdenii lactate utilization due to the transcriptional regulation of metabolic genes, and the lactate utilization in M. elsdenii was more sensitive to pH changes than to the substrate lactate level. In addition, compared with associations based on statics data, associations discovered from dynamics data showed greater significance and gave additional explanations regarding the relationships between bacterial competition and OA accumulation.

Highlights

Current intensive livestock management systems encourage the inclusion of large amounts of cereal grains in the diets of ruminants to support a high production rate and enhance cost efficiency
Acute rumen acidosis is characterized by a dramatic reduction in the ruminal pH below 5.0, and subacute rumen acidosis (SARA) is defined as periods of moderately depressed ruminal pH lower than 5.8 for 4 h or more after feeding, while the rumen pH should normally be above 5.8 (Nagaraja and Titgemeyer, 2007; Loor et al, 2016)
A normal model was characterized by a slight drop of pH with time and became stable, but remained above 6.0 (Figure 1B); a SARA model showed that pH decreased first and recovered, with a pH range from 5.8 to 5.9 for a duration of 5 h (Figure 1B); a acute rumen acidosis (ARA) model showed that pH declined quickly with time, reaching a final pH of 4.7 at 22.5 h (Figure 1B)

Summary

Introduction

Current intensive livestock management systems encourage the inclusion of large amounts of cereal grains in the diets of ruminants to support a high production rate and enhance cost efficiency. Streptococcus bovis and Lactobacilli spp. to produce pyruvate and converting to organic acids (OA) (Wang et al, 2015; Mickdam et al, 2016) In this process, S. bovis, which is the most prominent amylolytic bacterium in the rumen, proliferates rapidly and primarily produces lactate while limit amount of volatile fatty acids (VFA) (Russell and Hino, 1985; Asanuma and Hino, 2000; Hernández et al, 2014; Chen et al, 2016a,b,c; Chen and Wang, 2016). Megasphaera elsdenii is an ecologically important rumen bacterium that metabolizes lactate and relieves rumen acidosis (RA) induced by a high-grain-diet.

Methods

Results

Discussion

Conclusion