Multiple lactate dehydrogenase activities of the rumen bacterium Selenomonas ruminantium

Abstract

The lactate utilizing strain of Selenomonas ruminantiurn 5934e was found to contain three lactate dehydrogenase (LDH) activities in sonicated cell extracts. One activity, an NAD dependent L-LDH (L-nLDH) was measured a t 15-fold greater levels in extracts of cells grown to mid-exponential phase on glucose compared to cells grown to the equivalent growth stage on DL-lactate. A second nLDH activity specific for D-lactate (D-nLDH) was detected a t similar levels in both lactate-grown cell extracts and glucose-grown cell extracts. The third activity, an NAD independent DLDH (D-iLDH) was very low in cells grown on glucose but was induced more than 10-fold when DL-lactate was used as the carbon source. The three LDH activities could be separated by gel filtration. Recovery of the activities was low due to the apparent instability of the enzymes a t 4 "C, which was most pronounced in the case of the D-iLDH. A Km for lactate of 0 5 mM was estimated for the D-ILDH and this was considerably lower than the values of 45 mM and 70 mM measured for L-nLDH and D-nLDH respectively. It is proposed that the D-iLDH may be largely responsible for the formation of pyruvate in lactate-grown cells of 5. ruminantiurn strain 5934e. Three other lactate utilizing strains of S. ruminantiurn, HD4, 5521C1 and JW13 exhibited a similar profile of LDH activities to strain 5934e when grown on glucose and DL-lactate.

Phylogenetic distribution of three pathways for propionate production within the human gut microbiota

“…Veillonella parvula gains additional energy from succinate in the presence of lactate as the main growth substrate (Janssen, 1992), whereas Phascolarctobacterium succinatutens, isolated from human faeces, can grow on succinate alone (Watanabe et al, 2012). Selenomonas ruminantium strains isolated from the rumen produce lactate, acetate and propionate from carbohydrates, and some are also able to utilise lactate for growth (Bryant, 1956;Gilmour et al, 1994). This class of bacteria remains understudied in the human gut and it remains to be established which genera dominate in this ecosystem.…”

Lactate racemase is a nickel-dependent enzyme activated by a widespread maturation system

“…However, when only one stereospecific lactate dehydrogenase is present, production or utilization of the other isomer may proceed by lactate isomerization involving a specific lactate racemase (Lar) 5 . This activity was first reported in Clostridium beijerinckii (formerly C. butylicum ) 6 and, since then, it has been identified in several species including lactobacilli 7-10 .…”

The Rumen Microbial Ecosystem

“…In lactate-utilizing strains grown on glucose, accumulated lactate can be utilized to form acetate and propionate. It should be noted that the commonly studied strain HD4 exhibits poor growth on lactate (Gilmour et al, 1994) and poor decarboxylation rates for succinate (Strobel and Russell, 1991) by comparison with more recently isolated strains. Another important activity of S. ruminantium is the decarboxylation of succinate to propionate (Strobel and Russell, 1991).…”

“…Cytochrome b is present, but menaquinones and ubiquinones are absent (Stackebrandt et ai., 1985). A cofactor-independent LDH activity may function in lactate utilization, while the main NAD-dependent LDH functions in lactate formation (Gilmour et al, 1994). In lactate-utilizing strains grown on glucose, accumulated lactate can be utilized to form acetate and propionate.…”