Regulation of lactate dehydrogenase synthesis in a ruminal bacterium, Streptococcus bovis.

Abstract

Lactate dehydrogenase (LDH) was purified from three strains of Streptococcus bovis, and the gene Idh was cloned and sequenced. The Idh of S. bovis from a goat (TH1) was different from the Idhs of two other strains from cattle (TH2, JB1) in that Asp220 was substituted for Glu. Northern blot analysis revealed that the LDH-mRNA of S. bovis was approximately 1.0 kbp, which was transcribed in a monocistronic fashion. When cells were grown at pH 6.9 in a batch culture, the level of Idh transcript decreased as the growth phase changed; from exponential growth to the cessation of growth. The level of Idh transcript was higher in cells grown at pH 4.5 than at pH 6.9. This observation was consistent with the amounts of LDH in cells and the percentages of lactate produced. These results support the hypothesis that S. bovis regulates LDH synthesis at the transcriptional level probably in response to intracellular pH.

Effects of pH and Energy Supply on Activity and Amount of Pyruvate Formate-Lyase in Streptococcus bovis

“…The results obtained in this experiment were essentially consistent with our previous results showing that the level of pfl-mRNA changed with culture conditions (4). The synthesis of PFL appears to be regulated at the transcriptional level in response to growth conditions, as observed for LDH synthesis (3,4). However, the changes in PFL activity reported in the previous paper (4) were much greater than the changes in PFL protein.…”

“…We previously reported that S. bovis increases the percentage of lactate by increasing the amount of LDH in response to low pH and an excess energy supply (2)(3)(4) and that LDH synthesis is regulated at the transcriptional level (3,4). The increase in lactate production at low pH is explained in part by the fact that the optimal pH of S. bovis LDH is 5.5, which is similar to the intracellular pH when the extracellular pH is 4.7 (2,19).…”

“…The polyclonal antibody against PFL was the primary antibody, alkaline phosphatase-conjugated anti-rabbit goat immunoglobulin G (Bio-Rad) was the secondary antibody, and 5-bromo-4-chloro-3-indolyl phosphate and nitroblue tetrazolium were the substrates used to visualize PFL. The amounts of PFL were estimated with a Fluor-S Multi Imager (Bio-Rad) as described previously (3).…”

Molecular characterization and transcriptional regulation of nitrate reductase in a ruminal bacterium, Selenomonas ruminantium

“…Western and northern blot analyses were performed as described previously (Asanuma and Hino, 2001;Asanuma et al, 1997). Probes specific to S. ruminantium narG, H, J, I, and K (see below) were designed from their open reading frames (ORFs).…”

Molecular Characterization of CcpA and Involvement of This Protein in Transcriptional Regulation of Lactate Dehydrogenase and Pyruvate Formate-Lyase in the Ruminal Bacterium Streptococcus bovis

“…The activities of LDH and PFL are regulated by allosteric effectors, such as fructose 1,6-bisphosphate (FBP), phosphoenolpyruvate, and triose phosphates, and also by the amounts of enzyme proteins (1,2,3). The synthesis of both enzymes is regulated at the transcriptional level (6,7). S. bovis increases lactate production by increasing LDH synthesis and simultaneously decreases formate production by decreasing PFL synthesis in response to a drop in the pH and an excess energy supply (2,6,7).…”