<i>Vpar_1595</i> encodes malate–lactate transhydrogenase: The first step in lactate metabolism within the genus <i>Veillonella</i>

The genus Veillonella plays a pivotal role in human oral microbiota and biofilm formation. The role of these bacteria is to act as intermediaries, which they do partly by metabolizing L-lactate. Interestingly, their first step in lactate metabolism is catalyzed by malate‒lactate transhydrogenase (MLTH), an enzyme so far unique to the genus Veillonella and one whose sequence is yet unknown. Here, we identified the elusive MLTH sequence from a strain of Veillonella parvula and its corresponding gene Vpar_1595 based primarily on enzyme purification and LC‒MS/MS analysis, with the purified MLTH matching the theoretical Vpar_1595 protein spectrum with a MASCOT score of 4657. In addition, we show that both the molecular weight of 40 kDa and the predicted amino acid composition of Vpar_1595 correspond to the MLTH described in previous reports. We then perform a phylogenetic analysis and identify 88 putative MLTH-encoding genes within the genus Veillonella, showing that it indeed forms a distinct clade. This work provides the first molecular identification of the Veillonella malate–lactate transhydrogenase, establishing a genetic basis for a key metabolic step in oral biofilm formation. These findings open the door to study MLTH's evolutionary origins and its potential as a target for modulating oral microbial interactions.