Suppression of quorum sensing-mediated cell autolysis for highly efficient lactic acid production by Lactobacillus paracasei LYS2.

Deciphering the synergistic mechanism of quorum sensing and sulfate-reducing bacteria for directed acetate conversion during sludge fermentation.

The restricted bioconversion of C3-C5 short-chain fatty acids (SCFAs) to acetate due to thermodynamic limitations is the main bottleneck during sludge fermentation. To alleviate this constraint, this study developed an optimized approach by integrating quorum sensing regulation with incomplete-oxidation sulfate-reducing bacteria (io-SRB) to improve the selective conversion of carbon towards acetate. The results revealed that the addition of 5 μM C8-HSL combined with io-SRB led to the highest SCFAs and acetate production at 141.9 mg COD/g VSS and 87.2 mg COD/g VSS at 5 d, which was 37% and 37% higher than the group without C8-HSL addition, while increase the C8-HSL dosage had no significant promotion of SCFAs production. C8-HSL effectively accelerated the efficient utilization of soluble carbohydrates and proteins during sludge fermentation, and functional group analysis further confirmed its promotional effect on the biotransformation of macromolecular organic matter throughout the fermentation process. Functional microbes, i.e., hydrolytic bacteria, acid-producing bacteria, and io-SRB (e.g., Desulfobulbus and Desulfovibrio), were enriched in the 5 μM C8-HSL system. The molecular ecological network and Mantel analysis revealed cooperative interactions among these functional microorganisms. Moreover, the synergistic effects of exogenous C8-HSL with io-SRB enhanced the expression of key functional genes involved in glycolysis, amino-acid metabolism, and acetate synthesis pathways. These findings may improve the understanding of the biological transformation mechanisms of sludge organic matter, and provide useful theoretical support for the efficient production of value-added products from sludge fermentation.

Harnessing natural diversity of Saccharomyces cerevisiae for enhanced resistance to weak acids

Abstract The production of second-generation bioethanol from lignocellulosic biomass is a promising solution for sustainable energy, yet it faces significant challenges also due to the inhibitory effects of weak acids released during biomass pretreatment, particularly acetic, formic and levulinic acids. This review describes the ability of Saccharomyces cerevisiae, with a focus on natural isolates, in overcoming these challenging compounds. Indeed, natural isolates exhibit greater genetic and phenotypic diversity than laboratory and industrial strains, offering unique traits such as enhanced stress tolerance, metabolic efficiency, and adaptive responses to weak acids. This investigation explores the transcriptional and genomic mechanisms underlying yeast adaptive responses, emphasizing key regulatory networks and resistance pathways, including drug H+ antiporters, Reactive Oxygen Species (ROS) mitigation strategies, and membrane composition adjustments. Strategies for strains improvement, involving adaptive laboratory evolution (ALE), genome shuffling, and hybridization, are also discussed as complementary approaches to develop robust yeast capable of thriving under stressful industrial fermentation conditions. The integration of these techniques, along with genomic and transcriptomic insights, provides a comprehensive framework for engineering high-performance yeast strains. Ultimately, this review underscores the potential of leveraging natural diversity and innovative biotechnological strategies to advance the scalability and efficiency of lignocellulosic bioethanol production through S. cerevisiae fermentation. Graphical abstractMulti-panel diagram illustrating Saccharomyces cerevisiae isolates, genomic exploration, and metabolic engineering techniques.The figure features three connected panels detailing research on Saccharomyces cerevisiae. The first panel illustrates yeast cell icons with phenotypic traits: "High fermentative," "Weak acid resistant," "High secretory pathway," "Thermotolerant," and "Osmotic tolerant," with a glucose structure below. The second showcases a circular diagram of a "Mosaic genome," "Copy Number Variations," and single nucleotide polymorphisms (SNPs), with a heatmap for transcriptomics. The third illustrates metabolic engineering techniques, including CRISPR/Cas9, genome editing, Delta-integration, and transformation within yeast cells. STATEMENT OF SIGNIFICANCE Weak acids represent major inhibitory compounds in lignocellulosic fermentations, affecting the industrial viability of second-generation bioethanol. While most research has focused on laboratory or engineered strains, natural isolates of Saccharomyces cerevisiae can be still considered a resource of unexplored tolerance traits. This review highlights how omics-based insights into natural strains’ adaptive responses provide novel opportunities for metabolic engineering, particularly in weak acid resistance. By integrating genetic variability, ploidy diversity, and systems biology perspectives, a yeast strain capable of overcoming industrial-relevant stresses such as weak acids can be designed, advancing sustainable bioethanol production and expanding the scope of microbial biotechnology.

Cultivation-dependent effects of quorum sensing signals on a lactic acid and chain-elongating bacterium

Evaluation of Saccharomyces cerevisiae Yeast Cell Wall as a Microbial-Derived Prebiotic Substrate for Enhancing the Functional Properties of Lactic Acid Bacteria

Saccharomyces cerevisiae yeast cell wall (SC), a fermentation by-product rich in β-glucans, mannans, and mannoproteins, was evaluated as a sustainable microbial-derived prebiotic for Lacticaseibacillus paracasei, Lacticaseibacillus rhamnosus, and Levilactobacillus brevis. FTIR confirmed the characteristic structure of SC. Its effects on probiotic functionality were assessed through growth kinetics, biomass production, antimicrobial, antioxidant, enzymatic, and organic acid analyses, using MRS and inulin as controls. SC significantly enhanced biomass production, with the highest yield obtained for L. paracasei in 10% SC (5.85 g), compared with 3.75 g in MRS. L. rhamnosus showed superior antimicrobial activity in SC supplemented medium and inhibited Escherichia coli and Staphylococcus aureus (up to 4 mm), while L. paracasei exhibited 76.06% DPPH scavenging activity. L. rhamnosus showed the highest lipase (5.80 U/mL) and lactic acid (11.80 g/L) production, whereas L. brevis produced the highest acetic (0.56 g/L) and butyric acids (0.0050 g/L). These findings demonstrated that SC is a promising sustainable microbial-derived prebiotic for synbiotic fermentation and valorization of industrial yeast by-products.

Lactic Acid Bacteria-Derived γ-Aminobutyric Acid: From Targeted Screening and Biosynthesis to Functional Food Applications and Health Benefits

γ-Aminobutyric acid (GABA) is a non-proteinogenic amino acid that acts as a major signaling molecule across the nervous, cardiovascular, and immune systems. While GABA has historically been produced via chemical synthesis or plant extraction, microbial fermentation using lactic acid bacteria (LAB) provides a safe, sustainable, and food-grade alternative. This review details the recent progress of LAB-derived GABA, covering the workflow from strain selection to functional food applications. We discuss how modern screening methods combine high-throughput phenotypic testing with genomic mining of the gad operon to efficiently identify high-yielding strains. The biochemical mechanisms of the GABA shunt are also explained, alongside recent CRISPR-based metabolic engineering efforts designed to bypass natural yield limits. Furthermore, we address practical industrial challenges—such as the poor proteolytic ability of key producers like Levilactobacillus brevis—and evaluate viable solutions, including symbiotic co-cultures and optimized downstream purification steps. The review then summarizes the specific health benefits of dietary LAB-derived GABA, focusing on its ability to relieve anxiety via the microbiota-gut–brain axis, control blood pressure, and regulate immunity. Finally, we analyze the current regulatory and sensory hurdles, highlighting how integrating multi-omics data can help establish LAB-derived GABA as a reliable ingredient for functional foods and personalized nutrition.

Unravelling Nutritional Drivers of Biohydrogen Production from Syngas Fermentation in a Natural Microbial Consortium

Syngas fermentation offers a promising route for biological hydrogen (H2) production, yet industrial application is restrained by low yields and limited understanding of nutrient requirements in natural microbial consortia. This study investigated the macro- and micronutrient roles influencing carbon monoxide (CO)-to-H2 conversion in a thermophilic consortium using a medium for thermophilic, anaerobic, and carboxydotrophic microorganisms as the starting formulation. Yeast extract and trace element solution showed the strongest positive associations with H2 production, supplying essential vitamins, nitrogen, and enzymatic cofactors, including Ni and Fe, for CO dehydrogenase and hydrogenase activity. In contrast, sulfide solution and NH4Cl showed inhibitory trends, likely through redox imbalance and hydrogenase suppression. Optimizing the concentrations of yeast extract (7.5 g/L) and trace element solution (4 mL/L) increased H2 production by 53% (3.59 ± 0.06 mmol), although the elevated volatile fatty acid concentration indicated partial reliance on organic carbon metabolism. Reducing yeast extract to 0.5 g/L and supplementing with Wolin’s vitamin solution maintained equivalent productivity while reducing medium costs by approximately 45% relative to DSMZ 507. These findings suggest that precise nutrient management plays a decisive role in governing CO conversion toward H2, providing critical insights for scalable, economically viable biohydrogen production from syngas fermentation.