The primary pathway for lactate oxidation in Desulfovibrio vulgaris

Abstract

The ability to respire sulfate linked to lactate oxidation is a key metabolic signature of the Desulfovibrio genus. Lactate oxidation by these incomplete oxidizers generates reductants through lactate dehydrogenase (LDH) and pyruvate-ferredoxin oxidoreductase (PFOR), with the latter catalyzing pyruvate conversion into acetyl-CoA. Acetyl-CoA is the source of substrate-level phosphorylation through the production of ATP. Here, we show that these crucial steps are performed by enzymes encoded by a nonacistronic transcriptional unit named now as operon luo (for lactate utilization operon). Using a combination of genetic and biochemical techniques, we assigned a physiological role to the operon genes DVU3027-28 and DVU3032-33. The growth of mutant Δ26-28 was highly disrupted on D-lactate, whereas the growth of mutant Δ32-33 was slower on L-lactate, which could be related to a decrease in the activity of D-lactate or L-lactate oxidase in the corresponding mutants. The DVU3027-28 and DVU3032-33 genes thus encode functional D-LDH and L-LDH enzymes, respectively. Scanning of the genome for lactate utilization revealed several lactate permease and dehydrogenase homologs. However, transcriptional compensation was not observed in any of the mutants except for lactate permease. Although there is a high degree of redundancy for lactate oxidase, it is not functionally efficient in LDH mutants. This result could be related to the identification of several operon enzymes, including LDHs, in the PFOR activity bands, suggesting the occurrence of a lactate-oxidizing supermolecular structure that can optimize the performance of lactate utilization in Desulfovibrio species.

Antimicrobial Effects of Free Nitrous Acid on Desulfovibrio vulgaris: Implications for Sulfide-Induced Corrosion of Concrete

“…This downregulation of the luo operon genes during FNA exposure is logical when the cells' respiratory activities were lowered, as we observed. Additionally, these findings further support the involvement of the recently described luo operon in lactate oxidation (32).…”

“…However, the expression levels (RPKM values) of these genes in the presence of FNA were extremely low (Table 3); thus, this questions the involvement of the respective coded proteins in lactate oxidation. Recently, genes of the luo operon are deemed to be responsible for lactate oxidation in D. vulgaris rather than DVU0600, DVU1569, and DVU1570 (32). In this study, we detected downregulation of most genes in the luo operon when exposed to FNA (Table 3), and importantly, these genes had high expression values when lactate and sulfate utilization and when acetate and sulfide production were active (Table 3 and Fig.…”

“…Recently, an operon has been described for lactate oxidation genes (luo) in D. vulgaris (32). This includes the genes DVU3026 for lactate permease, DVU3027, DVU3028, DVU3032, and DVU03033 for lactate dehydrogenase subunits, DVU3025 for pyruvate-ferredoxin oxidoreductase, DVU3030 for acetate kinase, and DVU3029 for phosphate acetyltransferase.…”

Growth of an anaerobic sulfate‐reducing bacterium sustained by oxygen respiratory energy conservation after O2‐driven experimental evolution

“…For cDNA synthesis, 1 μg of total RNA and 0.5 μg of random primers (Promega) were used with GoScript™ Reverse transcriptase (Promega) according to the manufacturer's instructions. Quantitative-real time PCR (qPCR) were performed as previously described (Vita et al, 2015).…”

Constraint‐based modelling captures the metabolic versatility of Desulfovibrio vulgaris

“…The complexity of the electron transfer system has complicated a fully reductionist understanding of the metabolic flexibility of D. vulgaris Hildenborough growth under different environmental conditions. Even with more recent advances in genetic methods (Fels et al, 2013;Kuehl et al, 2014) and gene expression analyses (Walker et al, 2009;Pereira et al, 2008;Meyer et al, 2013b), the model of the electron transfer system sustaining growth by sulfate respiration is still evolving (Keller and Wall, 2011;Pereira et al, 2011;Keller et al, 2014) with improved understanding of the coupling mechanisms of the different interacting redox proteins, for example, the multiple lactate dehydrogenases (Ldhs) encoded in the genome of D. vulgaris Hildenborough (Keller and Wall, 2011;Meyer et al, 2013b;Keller et al, 2014;Vita et al, 2015). Reported as membraneassociated proteins based on a study of Desulfovibrio desulfuricans, the Ldhs were initially assumed to energetically couple lactate oxidation with reduction of the menaquinone pool (Czechowski, M.H, and Rossmoore, 1990).…”