Project description:Food waste is a major source of environmental pollution, as its landfills attribute to greenhouse gas emissions. This study developed a robust upcycling bioprocess that converts food waste into lactic acid through autochthonous fermentation and further produces biodegradable polymer polyhydroxybutyrate (PHB). Food can be stored without affecting its bioconversion to lactic acid, making it feasible for industrial application. Mapping autochthonous microbiota in the food waste fermentation before and after storage revealed lactic-acid-producing microorganisms dominate during the indigenous fermentation. Furthermore, through global transcriptomic and gene set enrichment analyses, it was discovered that coupling lactic acid as carbon source with ammonium sulfate as nitrogen source in Cupriavidus necator culture upregulates pathways, including PHB biosynthesis, CO2 fixation, carbon metabolism, pyruvate metabolism, and energy metabolism compared to pairing with ammonium nitrate. There was ∼90 % PHB content in the biomass. Overall, the study provides crucial insights into establishing a bioprocess for food waste repurposing.
Project description:The presence of anti-microbial phenolic compounds, such as the model compound ferulic acid, in biomass hydrolysates poses significant challenges to the widespread use of biomass in conjunction with whole cell biocatalysis or fermentation. Currently, these inhibitory compounds must be removed through additional downstream processing to create feedstock suitable for most industrially important microbial strains. This study explores the high ferulic acid tolerance in Lactobacillus brevis (L. brevis), a lactic acid bacteria often found in fermentation processes, by global transcriptional response analysis. The transcriptional profile of L. brevis under ferulic acid stress reveals that the presence of ferulic acid primarily triggers the expression of membrane proteins to counteract ferulic acid induced changes in membrane fluidity and ion leakage, in the midst of a generalized stress response. Several promising routes for understanding phenolic acid tolerance have been identified based upon these findings. These insights may be used to guide further engineering of model industrial organisms to better tolerate phenolic compounds in processed biomass.
Project description:Lactococcus lactis is the main bacterium used for food fermentation and is a candidate for probiotic development. In addition to fermentation growth, supplementation with heme in aerobic conditions activates a cytochrome oxidase, which promotes respiration metabolism. In contrast to fermentation in which cells consume energy to produce mainly lactic acid, respiration metabolism dramatically changes energy metabolism, such that massive amounts of acetic acid and acetoin are produced at the expense of lactic acid. Our goal was to investigate the metabolic changes that correlate with significantly improved growth and survival during respiration growth. Using transcriptional time course analyses, mutational analyses, and promoter reporter fusions, we uncover two main pathways that can explain the robust growth and stability of respiration cultures: The acetate pathway contributes to biomass yield in respiration, without affecting medium pH. The acetoin pathway allows cells to cope with internal acidification, which directly affects cell density and survival in stationary phase. Our results suggest that manipulation of these pathways could lead to fine tuning respiration growth, with improved yield and stability.
Project description:Lactic acid bacteria (LAB) belong to an economically important group of Gram-positive microorganisms, whose main characteristic is the production of lactic acid by carbohydrates fermentation. Lactobacillus paraplantarum CRL 1905 is a LAB isolated from quinoa sourdoughs with biotechnological potential as a starter or probiotic. Inorganic phosphate (Pi) is an essential nutrient for most bacteria cell functions and it is involved in many regulatory processes. The aim of the project was to evaluate the influence of environmental Pi concentration in different physiological and molecular aspects of the CRL 1905 strain. Phenotypic and proteomic data provide new insights to understand the adaptations in several metabolic pathways that CRL 1905 experiments in response to differential Pi conditions.
Project description:The present study aims to explore chemostat-based transcriptome analysis of mixed cultures by investigating interactions between the yeast S. cerevisiae and the lactic acid bacterium L. bulgaricus . S. cerevisiae and L. bulgaricus are both frequently encountered in kefir, a fermented dairy product. In the context of this study, this binary culture serves as a model for the many traditional food and beverage fermentation processes in which yeasts and lactic acid bacteria occur together. The design of the cultivation conditions was based on the observation that L. bulgaricus, but not S. cerevisiae, can use lactose as a carbon source for growth and that S. cerevisiae, but not L. bulgaricus, can grow on galactose that is released upon hydrolysis of lactose by the bacterial β-galactosidase. Mixed populations of yeasts and lactic acid bacteria occur in many dairy, food and beverage fermentations, but knowledge about their interactions is incomplete. In the present study, interactions between Saccharomyces cerevisiae and Lactobacillus delbrueckii subsp. bulgaricus, two microorganisms that co-occur in kefir fermentations, were studied during anaerobic growth on lactose. By combining physiological and transcriptome analysis of the two strains in the co-cultures, five mechanisms of interaction were identified. 1. L. bulgaricus hydrolyses lactose, which cannot be metabolized by S. cerevisiae, to galactose and glucose. Subsequently, galactose, which cannot be metabolized by L. bulgaricus, is excreted and provides a carbon source for yeast. 2. In pure cultures, L. bulgaricus only grows at increased CO2 concentrations. In anaerobic mixed cultures, the yeast provides this CO2 via alcoholic fermentation. 3. Analysis of amino acid consumption from the defined medium indicated that S. cerevisiae supplied alanine to the bacteria. 4. A mild but significant low-iron response in the yeast transcriptome, identified by DNA microarray analysis, was consistent with the chelation of iron by the lactate produced by L. bulgaricus. 5. Transcriptome analysis of L. bulgaricus in mixed cultures showed an overrepresentation of transcripts involved in lipids metabolism suggesting either a competition of the two microorganisms for fatty acids, or a response to the ethanol produced by S. cerevisiae.