Effect of High Hydrostatic Pressure on Stress-Related dnaK, hrcA, and ctsR Expression Patterns in Selected Lactobacilli 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.

Depiction of the In Vitro and Genomic Basis of Resistance to Hop and High Hydrostatic Pressure of Lactiplantibacillus plantarum Isolated from Spoiled Beer

Among the beer-spoiling microorganisms, the dominant ones belong to the genera Lactobacillus, Leuconostoc, Oenococcus, and Pediococcus. It is assumed that resistance to hop bitters correlates with resistance to other factors and can significantly impact the brewing industry. Beer preservation with high hydrostatic pressure eliminates the spoiling microorganisms while preserving all desired properties of the beer. Here, we present comprehensive in vitro and genomic analysis of the beer-spoiling Lactiplantibacillus plantarum KKP 3573 capacity to resist hop and high hydrostatic pressure. Lp. plantarum KKP 3573 is a strain isolated from spoiled beer. Our finding suggests that the growth rate of the strain depends on the medium variant, where a small concentration of beer (5 IBU) stimulates the growth, suggesting that the limited concentration has a positive effect on cell growth. At the same time, increased concentrations of 20 IBU, 30 IBU, and pure beer 43.6 IBU decreased the growth rate of the KKP 3573 strain. We observed that higher extract content in the pressurized beer increased microbial survivability. The wort and Vienna Lager beer can stimulate the baroprotective effect. The taxonomy of the novel strain was confirmed after whole genome sequencing (WGS) and comparative genomic analysis. More specifically, it contains a chromosome of 3.3 Mb with a GC content of 44.4%, indicative of the Lp. plantarum species. Accordingly, it possesses high genomic similarity (>98%) with other species members. Annotation algorithms revealed that the strain carries several genes involved in resistance to stress, including extreme temperature, hop bitters and high pressure, and adaptation to the brewing environment. Lastly, the strain does not code for toxins and virulence proteins and cannot produce biogenic amines.

Genomic Analysis and In Vitro Investigation of the Hop Resistance Phenotype of Two Novel Loigolactobacillus backii Strains, Isolated from Spoiled Beer

Loigolactobacillus backii is an important beer-spoiling species, exhibiting high hop tolerance. Here, we present the annotated whole genome sequence of two recently isolated strains, Lg. backii KKP 3565 and KKP 3566. Firstly, to study the genetic basis of the persistence of the two isolates in beer, a comprehensive bioinformatic analysis ensued. Their chromosome map was constructed, using whole-genome sequencing and assembly, revealing that the two strains carry genomes with a length of 2.79 Mb with a GC content of 40.68%. An average nucleotide identity (ANI) analysis demonstrated that the novel strains possess unique genomic sequences, also confirming their classification into the Lg. backii species. Their genome harbors numerous insertion sequences and plasmids, originating from other beer-spoiling species. Regarding their adaptation in brewery environment, homologous genes that confer resistance to hop were spotted, while the impact of hop bitters and pure beer on bacterial growth was investigated, in vitro. In brief, low hop concentrations were found to induce the proliferation of strains, while a higher concentration negatively affected their growth. Nonetheless, their ability to survive in pure beer indicated their tolerance to high hop concentrations. These results offer insight into the capacity of Lg. backii KKP 3566 and Lg. backii KKP 3566 to tolerate the extreme conditions prevalent in the brewery environment.