Energetics and kinetics of lactate fermentation to acetate and propionate via methylmalonyl-CoA or acrylyl-CoA

Abstract

Fermentation balances and growth yields were determined with various bacteria fermenting lactate to acetate plus propionate either via methylmalonyl-CoA or via acrylyl-CoA. All strains fermented lactate to acetate plus propionate at approximately a 1:2 ratio. Growth yields of Propionibacterium freudenreichii were more than twice as high as those of Clostridium homopropionicum or Veillonella parvula. Hydrogen was formed as a side product to a significant extent only by V. parvula and Pelobacter propionicus; the latter formed hydrogen preferentially when using ethanol as substrate. Acrylyl-CoA reductase of C. homopropionicum and Clostridium neopropionicum was found nearly exclusively in the cytoplasm thus confirming that this reduction step is unlikely to be involved in energy conservation. C. homopropionicum exhibited higher K S and higher W max values, as well as higher specific substrate turnover rates than P. freudenreichii. The results allow us to conclude that C. homopropionicum using the acrylyl-CoA pathway with low growth yield obtains its specific competitive advantage compared to P. freudenreichii not through higher substrate affinity or metabolic shift toward enhanced acetate-plus-hydrogen formation but through faster specific substrate turnover. ß

Bacterial Stern layer diffusion: experimental determination with spectral induced polarization and sensitivity to nitrite toxicity

“…The biomass increase was matched by increasing σ″ signals in both SIP columns (G1 and G2). Cell counts for the column sacrificially sampled immediately before phase II are omitted, because propionate was detected, suggesting that the bacteria fermented lactate (Seeliger, Janssen and Schink, ), and that the column did not behave as a replicate. Temporal trends in peak‐ σ″ from a non‐growth control column, inoculated with S. oneidensis , but devoid of NO 3 − and lactate, are compared with the SIP measurements in column G2 in Supporting Information Fig.…”

Two beta‐alanyl‐CoA:ammonia lyases in Clostridium propionicum

“…A possible function of acryloyl‐CoA as terminal acceptor in an electron transport phosphorylation similar to fumarate reductase [32] appears unlikely as it has been shown that acryloyl‐CoA reductase is a soluble enzyme, which uses NADH rather than menaquinol as electron donor. Growth experiments with two lactate fermenting organisms confirm the conservation of only one ATP/acetate via the acryloyl‐CoA pathway [33]. Clostridium homopropionicum ferments lactate via acryloyl‐CoA (Fig.…”

“…The latter pathway comprises additional electron transport phosphorylation via the oxidation of reduced ferredoxin and NADH by fumarate via menaquinol [32]. Hence, the low ATP yield in the β‐alanine fermentation by C. propionicum should increase the catabolic substrate flux, which in the presence of high β‐alanine concentrations enhances the growth rate [33] and probably keeps the concentration of the toxic acryloyl‐CoA at a low level.…”

Carboxylic acid production from ensiled crops in anaerobic solid‐state fermentation ‐ trace elements as pH controlling agents support microbial chain elongation with lactic acid

“…In periods with low lactic acid concentrations, most likely lactic acid was produced but instantly consumed by secondary processes. Lactic acid can be converted to acetic and propionic acid by microbes using the acrylyl‐CoA or the methylmalonyl‐CoA pathway or solely to acetic acid by heterotrophic homoacetogens exploiting lactate dehydrogenase, pyruvate decarboxylase and the Wood‐Ljungdahl pathway . Alternatively, the reduction to 1,2‐propanediol and ethanol is possible .…”