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

TITLE=Megasphaera elsdenii Lactate Degradation Pattern Shifts in Rumen Acidosis Models

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.00162

DOI=10.3389/fmicb.2019.00162

ISSN=1664-302X

ABSTRACT=<p><bold>Background:</bold><italic>Megasphaera elsdenii</italic> 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.</p><p><bold>Methods:</bold><italic>Megasphaera elsdenii</italic> was co-cultured with four lactate producers (<italic>Streptococcus bovis</italic>, <italic>Lactobacilli fermentum</italic>, <italic>Butyrivibrio fibrisolvens</italic>, and <italic>Selenomonas ruminantium</italic>) 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 <italic>Megasphaera elsdenii’s</italic> lactate degradation pattern and genes related to the lactate utilizing pathways in the continuous culture.</p><p><bold>Results and Conclusion:</bold> The positive growth of <italic>M. elsdenii</italic> and <italic>B. fibrisolvens</italic> 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 <italic>M. elsdenii</italic> lactate utilization due to the transcriptional regulation of metabolic genes, and the lactate utilization in <italic>M. elsdenii</italic> 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.</p>