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- Lactobacillus reuteri growth and fermentation under high pressure towards the production of 1,3-propanediolPublication . Mota, Maria J.; Lopes, Rita P.; Sousa, Sérgio; Gomes, Ana M.; Delgadillo, Ivonne; Saraiva, Jorge A.Lactobacillus reuteri is a lactic acid bacterium able to produce several relevant bio-based compounds, including 1,3-propanediol (1,3-PDO), a compound used in food industry for a wide range of purposes. The performance of fermentations under high pressure (HP) is a novel strategy for stimulation of microbial growth and possible improvement of fermentation processes. Therefore, the present work intended to evaluate the effects of HP (10–35 MPa) on L. reuteri growth and glycerol/glucose co-fermentation, particularly on 1,3-PDO production. Two different types of samples were used: with or without acetate added in the culture medium. The production of 1,3-PDO was stimulated at 10 MPa, resulting in enhanced final titers, yields and productivities, compared to 0.1 MPa. The highest 1,3-PDO titer (4.21 g L−1) was obtained in the presence of acetate at 10 MPa, representing yield and productivity improvements of ≈ 11 and 12%, respectively, relatively to the same samples at 0.1 MPa. In the absence of acetate, 1,3-PDO titer and productivity were similar to 0.1 MPa, but the yield increased≈26%. High pressure also affected the formation of by-products (lactate, acetate and ethanol) and, as a consequence, higher molar ratios 1,3-PDO:by-products were achieved at 10 MPa, regardless of the presence/absence of acetate. This indicates a metabolic shift, with modification of product selectivity towards production of 1,3-PDO. Overall, this work suggests that HP can be a useful tool to improve of 1,3-PDO production from glycerol by L. reuteri, even if proper process optimization and scale-up are still needed to allow its industrial application. It also opens the possibility of using this technology to stimulate other glycerol fermentations processes that are relevant for food science and biotechnology.
- Utilization of glycerol during consecutive cycles of Lactobacillus reuteri fermentation under pressure: the impact on cell growth and fermentation profilePublication . Mota, Maria J.; Lopes, Rita P.; Sousa, Sérgio; Gomes, Ana M.; Lorenzo, Jose M.; Barba, Francisco J.; Delgadillo, Ivonne; Saraiva, Jorge A.Exposure of bacterial cells to sub-lethal high pressure (HP) during growth and fermentation may promote development of new adaptive features, with potential biotechnological interest. The present work evaluated the effect of consecutive fermentation cycles under HP on Lactobacillus reuteri growth and glycerol/glucose co-fermentation. At all conditions tested (0.1, 10 and 25 MPa), 1,3-propanediol production from glycerol was enhanced over the cycles. The highest titers, yields and productivities were achieved at 10 MPa. In addition, the HP-cycles promoted shifts in by-product formation (ethanol, acetate and lactate), with different profiles according to the pressure. Ratios between 1,3-propanediol:by-products increased throughout the cycles, especially at 10 MPa, indicating shifts in metabolic selectivity. Data regarding the effects of HP-cycles on protein and nucleic acid leakage suggested that, in some cases, L. reuteri changed membrane permeability as a possible adaptation to HP. Overall, this work confirms that HP may be an useful tool to stimulate production of 1,3-propanediol, as well as other biocompounds.