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:Staphylococcus aureus is an important food poisoning bacterium. In food preservation, acidification is a well-known method. Permeant weak organic acids, like lactic and acetic acids, are known to be more effective against bacteria than inorganic strong acids (e.g., HCl). Growth experiments and metabolic and transcriptional analyses were used to determine the responses of a food pathogenic S. aureus strain exposed to lactic acid, acetic acid, and HCl at pH 4.5. Lactic and acetic acid stress induced a slower transcriptional response and large variations in growth patterns compared with the responses induced by HCl. In cultures acidified with lactic acid, the pH of the medium gradually increased to 7.5 during growth, while no such increase was observed for bacteria exposed to acetic acid or HCl. Staphylococcus aureus increased the pH in the medium mainly through accumulation of ammonium and the removal of acid groups, resulting in increased production of diacetyl (2,3-butanedione) and pyrazines. The results showed flexible and versatile responses of S. aureus to different types of acid stress. As measured by growth inhibition, permeant organic acid stress introduced severe stress compared with the stress caused by HCl. Cells exposed to lactic acid showed specific mechanisms of action in addition to sharing many of the mechanisms induced by HCl stress. Data is also available from http://bugs.sgul.ac.uk/E-BUGS-87
Project description:In this study, we performed an RNA-Seq transcriptomic analysis concerning acetic acid bacteria’s acid resistance mechanisms during a continuous and periodical industrial submerged vinegar fermentation process, where the acetic acid concentration fluctuates between ~8% and ~12%
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:Many food fermentations are carried out by mixed cultures of lactic acid bacteria. Interactions between strains are of key importance for the performance of these fermentations. Yoghurt fermentation by Streptoccus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (L.bulgaricus) is one of the best-described mixed culture fermentations. These species stimulate each other’s growth by the exchange of metabolites such as folic acid and carbon dioxide. Recently, post-genomic studies have been applied to reveal the global physiological response to mixed culture growth in S. thermophilus, but an in-depth molecular analysis of mixed culture growth of both strains remains to be established. Here we report the application of mixed culture transcriptome profiling and a systematic analysis of candidate interaction compounds on growth, which allowed the unraveling of the molecular responses associated with co-culture growth in batch of S. thermophilus CNRZ1066 and L. bulgaricus ATCC BAA-365 in milk. Comparisons of mono cultures versus mixed cultures, at four time-points in batch fermentation, and comparisons between the four time-points within each fermentation, all in duplicate
Project description:High concenHigh concentration acetic acid in the fermentation medium represses cell growth, metabolism and fermentation efficiency of Saccharomyces cerevisiae, which is widely used for cellulosic ethanol production. Our previous study proved that supplementation of zinc sulfate in the fermentation medium improved cell growth and ethanol fermentation performance of S. cerevisiae under acetic acid stress condition. However, the molecular mechanisms is still unclear. To explore the underlying mechanism of zinc sulfate protection against acetic acid stress, transcriptomic and proteomic analysis were performed. The changed genes and proteins are related to carbon metabolism, amino acid biosynthesis, energy metabolism, vitamin biosynthesis and stress responses. In a total, 28 genes showed same expression in transcriptomic and proteomic data, indicating that zinc sulfate affects gene expression at posttranscriptional and posttranslational levels.tration acetic acid in the fermentation medium represses cell growth, metabolism and fermentation efficiency of Saccharomyces cerevisiae, which is widely used for cellulosic ethanol production. Our previous study proved that supplementation of zinc sulfate in the fermentation medium improved cell growth and ethanol fermentation performance of S. cerevisiae under acetic acid stress condition. However, the molecular mechanisms is still unclear. To explore the underlying mechanism of zinc sulfate protection against acetic acid stress, transcriptomic and proteomic analysis were performed. The changed genes and proteins are related to carbon metabolism, amino acid biosynthesis, energy metabolism, vitamin biosynthesis and stress responses. In a total, 28 genes showed same expression in transcriptomic and proteomic data, indicating that zinc sulfate affects gene expression at posttranscriptional and posttranslational levels.