1,3-Propanediol dehydrogenases in Lactobacillus reuteri: impact on central metabolism and 3-hydroxypropionaldehyde production

Abstract

BackgroundLactobacillus reuteri metabolizes glycerol to 3-hydroxypropionaldehyde (3-HPA) and further to 1,3-propanediol (1,3-PDO), the latter step catalysed by a propanediol dehydrogenase (PDH). The last step in this pathway regenerates NAD+ and enables therefore the energetically more favourable production of acetate over ethanol during growth on glucose.ResultsA search throughout the genome of L. reuteri DSM 20016 revealed two putative PDHs encoded by ORFs lr_0030 and lr_1734. ORF lr_1734 is situated in the pdu operon encoding the glycerol conversion machinery and therefore likely involved in 1,3-PDO formation. ORF lr_0030 has not been associated with PDH-activity so far. To elucidate the role of these two PDHs, gene deletion mutant strains were constructed. Growth behaviour on glucose was comparable between the wild type and both mutant strains. However, on glucose + glycerol, the exponential growth rate of Δlr_0030 was lower compared to the wild type and the lr_1734 mutant. Furthermore, glycerol addition resulted in decreased ethanol production in the wild type and Δlr_1734, but not in Δlr_0030. PDH activity measurements using 3-HPA as a substrate revealed lower activity of Δlr_0030 extracts from exponential growing cells compared to wild type and Δlr_1734 extracts.During biotechnological 3-HPA production using non-growing cells, the ratio 3-HPA to 1,3-PDO was approximately 7 in the wild type and Δlr_0030, whereas this ratio was 12.5 in the mutant Δlr_1734.ConclusionThe enzyme encoded by lr_0030 plays a pivotal role in 3-HPA conversion in exponential growing L. reuteri cells. The enzyme encoded by lr_1734 is active during 3-HPA production by non-growing cells and this enzyme is a useful target to enhance 3-HPA production and minimize formation of the by-product 1,3-PDO.

Nonclinical and Clinical Enterococcus faecium Strains, but Not Enterococcus faecalis Strains, Have Distinct Structural and Functional Genomic Features

“…glycerol to 1,3-propanediol is associated with restoring redox balance in L. reuteri during anaerobic growth on glucose (32). The 1,3-propanediol pathway is dependent on adenosylcobalamin, the synthesis of which is mediated by cobO (ortholog_2934), an NCenriched gene.…”

“…faecium NC genomes also have greater numbers of genes involved in glycerol fermentation to 1,3-propanediol. Biosynthesis of 1,3-propanediol was reported for several lactic acid bacteria, including Lactobacillus reuteri (32), Lactobacillus brevis (33), and Lactobacillus buchnerii (33), but not E. faecium. The pathway from (chromosome) containing NC-and CL-enriched genes.…”

Effect of Lineage-Specific Metabolic Traits of Lactobacillus reuteri on Sourdough Microbial Ecology

“…In human-lineage strains of L. reuteri, glycerol is converted to 1,3-propanediol by glycerol dehydratase and 1,3-propanediol dehydrogenase to regenerate NAD ϩ (16,27). In this study, the glycerol dehydratase gene was truncated to disable glycerol metabolism in L. reuteri FUA3400 because of the possible presence of more than one 1,3-propanediol dehydrogenase in the genome (28). Truncation of the glycerol dehydratase avoids accumulation of the antimicrobially active intermediate reuterin; besides, the lack of propanediol dehydrogenase may be compensated for by other dehydrogenase enzymes with broad substrate specificity (29).…”

Glycerol and cobalamin metabolism in lactobacilli: relevance of the propanediol dehydrogenase pdh30

“…reuteri outside of the pdu operon [37]; nevertheless, a subsequent search throughout the genome of Lb. reuteri DSM 20016 revealed two putative PDHs encoded by ORFs lr_0030 and lr_1734 [38]. Although it may be regulated differently, the pdu operon is highly similar in Lb.…”

“…The corresponding enzyme encoded by lr_0030 seems to play a pivotal role in 3-HPA conversion in exponential growing Lb. reuteri cells [38].…”