1,2-propanediol metabolism by heterofermentative lactobacilli in sourdough

The conversion of lactate to 1,2-propanediol and 1,2-propanediol to propionate sustains viability and metabolic activity of stationaryphase cells of lactobacilli over weeks or even months. The pathway was described only in few lactobacilli, and factors regulating its expression remain poorly understood. This study investigated the metabolic pathways of 1,2-propanediol in heterofermentative lactobacilli, focusing on lentilactobacilli, levilactobacilli and furfurilactobacilli. Lentilactobacillus buchneri FUA3252 demonstrated high 1,2-propanediol production in modified MRS (mMRS) medium with lactate, while Furfurilactobacillus spp. exhibited minimal 1,2-propanediol synthesis but produced notable amounts of mannitol. In sorghum sourdough, Ff. cerealis C5 and Ff. rossiae FUA3124 showed increased 1,2-propanediol levels after prolonged fermentation, with Ff. cerealis C5 yielding 40 mmol/kg sourdough by day 7. The effect of pH and lactate on expression of aldA, which encodes lactaldehyde dehydrogenase, was inconsistent among the strains and incubation conditions. The expression of pduC, coding for propanediol utilization enzyme, was not different between mMRS and sorghum sourdoughs, and its expression was not altered by lactate concentrations. The expression of aldA was consistently increased during the stationary phase of growth, which conforms to the continuing conversion of lactate to 1,2-propanediol by stationary phase cells during extended (weeks or month) incubation. The study provides insights into the metabolic versatility of lactobacilli and their potential applications in food biotechnology.