Adaptation of Lacticaseibacillus rhamnosus CM MSU 529 to Aerobic Growth: A Proteomic Approach

Unraveling the Genetic Adaptations in Cell Surface Composition and Transporters of Lactiplantibacillus plantarum for Enhanced Acid Tolerance

This study employed adaptive laboratory evolution to improve the acid tolerance of Lactiplantibacillus plantarum, a vital strain in food fermentation and a potential probiotic. Phenotype and genomic analyses identified the overexpression of stress response proteins, ATP synthases, and transporters as pivotal in conferring acid tolerance to the evolved strains. These adaptations led to a shorter lag phase, improved survival rates, and higher intracellular pH values compared to the wild-type strain under acid stress conditions. Additionally, the evolved strains showed an increased expression of genes in the fatty acid synthesis pathway, resulting in a higher production of unsaturated fatty acids. The changes in cell membrane composition possibly prevented H+ influx, while mutant genes related to cell surface structure contributed to observed elongated cells and thicker cell surface. These alterations in cell wall and membrane composition, along with improved transporter efficiency, were key factors contributing to the enhanced acid tolerance in the evolved strains.

Strategies to enhance stress tolerance in lactic acid bacteria across diverse stress conditions

Lactic acid bacteria (LAB) hold significant importance in diverse fields, including food technology, industrial biotechnology, and medicine. As basic components of starter cultures, probiotics, immunomodulators, and live vaccines, LAB cells resist a variety of stressors, including temperature fluctuations, osmotic and pH shocks, exposure to oxidants and ultraviolet radiation, substrate deprivation, mechanical damage, and more. To stay alive in these adversities, LAB employ a wide range of stress response strategies supported by various mechanisms, for example rearrangement of metabolism, expression of specialized biomolecules (e.g., chaperones and antioxidants), exopolysaccharide synthesis, and complex repair and regulatory systems. LAB can coordinate responses to various stressors using global regulators. In this review, we summarize current knowledge about stress response strategies used by LAB and consider mechanisms of response to specific stressful factors, supported by illustrative examples. In addition, we discuss technical approaches to increase the stress resistance of LAB, including pre-adaptation, genetic modification of strains, and adjustment of cultivation conditions. A critical analysis of the recent findings in this field augments comprehension of stress tolerance mechanisms in LAB, paving the way for prospective research directions with implications in fundamental and practical areas.

Genomic and in-vitro characteristics of a novel strain Lacticaseibacillus chiayiensis AACE3 isolated from fermented blueberry

Numerous different species of LAB are used in different fields due to their unique characteristics. However, Lacticaseibacillus chiayiensis, a newly established species in 2018, has limited microorganism resources, and lacks comprehensive evaluations of its properties. In this study, L. chiayiensis AACE3, isolated from fermented blueberry, was evaluated by genomic analysis and in vitro assays of the properties. The genome identified genes associated with biofilm formation (luxS, ccpA, brpA), resistance to oxidative stress (tpx, trxA, trxB, hslO), tolerance to acidic conditions (dltA, dltC), resistance to unfavorable osmotic pressure (opuBB, gbuA, gbuB, gbuC), and adhesion (luxS, dltA, dltC). The AACE3 showed 112 unique genes, relative to the other three L. chiayiensis strains. Among them, the presence of genes such as clpP, pepO, and feoA suggests a possible advantage of AACE3 over other L. chiayiensis in terms of environmental adaptation. In vitro evaluation of the properties revealed that AACE3 had robust antibacterial activity against eight common pathogens: Streptococcus agalactiae, Staphylococcus aureus, Escherichia coli, Salmonella enteritidis, Salmonella choleraesuis, Shigella flexneri, Pseudomonas aeruginosa, and Klebsiella pneumoniae. In addition, AACE3 showed more than 80% survival rate in all tests simulating gastrointestinal fluid, and it exhibited high antioxidant capacity. Interestingly, the cell culture supernatant was superior to intact organisms and ultrasonically crushed bacterial extracts in all tests of antioxidant capacity. These results suggested that the antioxidant capacity may originate from certain metabolites and extracellular enzymes produced by AACE3. Moreover, AACE3 was a moderate biofilm producer due to the self-agglomeration effect. Taken together, L. chiayiensis AACE3 appears to be a candidate strain for combating the growing incidence of pathogen infections and antioxidant production.