Abstract
3-Hydroxypropionic acid (3-HP) is a novel antimicrobial agent against foodborne pathogens like Salmonella and Staphylococcus species. Lactobacillus reuteri converts glycerol into 3-HP using a coenzyme A-dependent pathway, which is encoded by propanediol utilization operon (pdu) subjected to catabolite repression. In a catabolite-repression-deregulated L. reuteri RPRB3007, quantitative PCR revealed a 2.5-fold increase in the transcripts of the genes pduP, pduW and pduL during the mid-log phase of growth. The production of 3-HP was tested in resting cells in phosphate buffer and growing batch cultures in MRS broth of various glucose/glycerol ratios. Due to the upregulation of pathway genes, specific formation rate of 3-HP in the mutant strain was found to be enhanced from 0.167 to 0.257 g per g of cell dry mass per h. Furthermore, formation of 3-HP in resting cells was limited due to the substrate inhibition by reuterin at a concentration of (30±5) mM. In batch cultures, the formation of 3-HP was not observed during the logarithmic and stationary phases of growth of wild-type and mutant strains, which was confirmed by NMR spectroscopy. However, the cells collected in these phases were found to produce 3-HP after washing and converting them to resting cells. Lactate and acetate, the primary end products of glucose catabolism, might be the inhibiting elements for 3-HP formation in batch cultures. This was confirmed when lactate (25±5 mM) or acetate (20±5 mM) were added to biotransformation medium, which prevented the 3-HP formation. Moreover, the removal of sodium acetate and glucose (carbon source for lactic acid production) was found to restore 3-HP formation in the MRS broth in a similar manner to that of the phosphate buffer. Even though the genetic repression was circumvented by the up-regulation of pathway genes using a mutant strain, 3-HP formation was further limited by the substrate and catabolite inhibition.
Highlights
3-Hydroxypropionic acid (3-HP) is a novel antimicrobial agent against foodborne pathogens like Salmonella and Staphylococcus species
Even though the genetic repression was circumvented by the up-regulation of pathway genes using a mutant strain, 3-HP formation was further limited by the substrate and catabolite inhibition
Lactobacillus reuteri is an attractive host for 3-HP synthesis as it is known for the production of its precursor molecule, 3-hydroxypropanaldehdye (3-HPA/ reuterin), from glycerol
Summary
3-Hydroxypropionic acid (3-HP) is a novel antimicrobial agent against foodborne pathogens like Salmonella and Staphylococcus species. The production of 3-HP was tested in resting cells in phosphate buffer and growing batch cultures in MRS broth of various glucose/glycerol ratios. Even though the genetic repression was circumvented by the up-regulation of pathway genes using a mutant strain, 3-HP formation was further limited by the substrate and catabolite inhibition. 3-Hydroxypropionic acid (3-HP) is a C3 β-hydroxy carboxylic acid and a structural isomer of lactic acid It is one of the novel antimicrobial compounds against foodborne pathogens like Salmonella and Staphylococcus species [1]. The 3-HP metabolic pathway of CRE mutant RPRB3007 was analysed quantitatively at transcript levels and the effect of mutation over 3-HP formation was studied in the resting cells and growing batch cultures
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