Effects of Glucose and Starch on Lactate Production by Newly Isolated Streptococcus bovis S1 from Saanen Goats

Abstract

When ruminants are fed high-concentrate diets, Streptococcus bovis proliferates rapidly and produces lactate, potentially causing rumen acidosis. Understanding the regulatory mechanisms of the metabolism of this species might help in developing dietary strategies to alleviate rumen acidosis. S. bovis strain S1 was newly isolated from the ruminal fluid of Saanen dairy goats and then used to examine the effects of glucose and starch on bacterial metabolism and gene regulation of the organic acid-producing pathway in cultures at a pH of 6.5. Glucose or starch was added to the culture medium at 1 g/liter, 3 g/liter (close to a normal range in the rumen fluid), or 9 g/liter (excessive level). Lactate was the dominant acid produced during the fermentation, and levels increased with the amount of glucose or starch in a dose-dependent manner (P < 0.001). The production of formate and acetate in the fermentation media fluctuated slightly with the dose but accounted for small fractions of the total acids. The activities of lactate dehydrogenase (LDH) and ␣-amylase (␣-AMY) increased with the starch dose (P < 0.05), but the ␣-AMY activity did not change with the glucose dose. The relative expression levels of the genes ldh, pfl (encoding pyruvate formate lyase), ccpA (encoding catabolite control protein A), and ␣-amy were higher at a dose of 9 g/liter than at 1 g/liter (P < 0.05). Expression levels of pfl and ␣-amy genes were higher at 3 g/liter than at 1 g/liter (P < 0.05). The fructose 1,6-diphosphate (FDP) concentration tended to increase with the glucose and starch concentrations. In addition, the S. bovis S1 isolate fermented glucose much faster than starch. We conclude that the quantities of glucose and soluble starch had a major effect on lactate production due to the transcriptional regulation of metabolic genes. IMPORTANCEThis work used a newly isolated S. bovis strain S1 from the rumen fluid of Saanen goats and examined the effects of glucose and soluble starch on organic acid patterns, enzyme activity, and expression of genes for in vitro fermentation. It was found that lactate was the dominant product from S. bovis strain S1, and the quantities of both glucose and starch in the medium were highly correlated with lactate production and with the corresponding changes in associated enzymes and genes. Therefore, manipulating the metabolic pathway of S. bovis to alter the dietary level of readily fermentable sugar and carbohydrates may be a strategy to alleviate rumen acidosis. Streptococcus bovis is the most prominent bacterium in the rumen. Because S. bovis is lactate producing and acid tolerant, it plays an important role in rumen acidosis (1). Our previous study with dairy cows demonstrated that under normal conditions, the population of S. bovis is small, resulting in an insignificant amount of lactate production that is quickly metabolized by lactate utilizers such as Selenomonas ruminantium and Megasphaera elsdenii (2, 3). However, when a high-concentrate diet is provided, the growth rate of S. bovis i...

Diet with a High Proportion of Rice Alters Profiles and Potential Function of Digesta-Associated Microbiota in the Ileum of Goats

“…Maybe the LDH is all used to neutralize LACT and further investigation is needed to explain this phenomenon. AMY activity of fermenting microorganisms is an important factor in the fermentation of starch to lactate [ 56 ]. Previous studies have demonstrated that the concentration of AMY was related to dry matter intake and nutrient composition, and more starch intake may enhance the AMY concentration in the small intestine [ 57 , 58 ].…”

GC–MS analysis of the ruminal metabolome response to thiamine supplementation during high grain feeding in dairy cows

“…The increasing glucose promotes the production of pyruvate in the rumen. On the other hand, pyruvate can be converted to lactate by lactate dehydrogenase (LDH) (Chen et al 2016 ) or converted to acetyl coenzyme-A and formate by pyruvate formate-lyase (PFL) (Asanuma and Hino 2000 ), then acetyl-CoA is converted either to acetate or ethanol. Under anaerobic condition, PFL is a central enzyme to degrade pyruvate to acetyl-CoA and the enzyme comprises the cofactors S-adenosylmethionine and thiamine diphosphate (TPP) (Knappe et al 1969 ).…”

Targeting the Hindgut to Improve Health and Performance in Cattle

“…In addition to overall proliferation, alterations in microbial ecology and dysbiosis occur, and losses in microbial richness and diversity in response to acidotic diets are observed in both rumen fluid and cecum digesta/feces [ 33 , 34 , 35 ]. As a result, not only fermentation rates, but also patterns change, enhancing lactate synthesis and buildup and further contributing to the pH decline [ 36 , 37 ].…”