Tripeptides From Casein Are Signal Molecules to Induce the Expression of the Extracellular Protease MCP-01 Gene in Marine Bacterium Pseudoalteromonas sp. SM9913

Multispecies biofilms in fermentation: Biofilm formation, microbial interactions, and communication

Food fermentation is driven by microorganisms, which usually coexist as multispecies biofilms. The activities and interactions of functional microorganisms and pathogenic bacteria in biofilms have important implications for the quality and safety of fermented foods. It was verified that the biofilm lifestyle benefited the fitness of microorganisms in harsh environments and intensified the cooperation and competition between biofilm members. This review focuses on multispecies biofilm formation, microbial interactions and communication in biofilms, and the application of multispecies biofilms in food fermentation. Microbial aggregation and adhesion are important steps in the early stage of multispecies biofilm formation. Different biofilm-forming abilities and strategies among microorganisms lead to several types of multispecies biofilm formation. The spatial distribution of multispecies biofilms reflects microbial interactions and biofilm function. Then, we discuss the intrinsic factors and external manifestations of multispecies biofilm system succession. Several typical interspecies cooperation and competition modes and mechanisms of microbial communication were reviewed in this review. The main limitations of the studies included in this review are the relatively small number of studies of biofilms formed by functional microorganisms during fermentation and the lack of direct evidence for the formation process of multispecies biofilms and microbial interactions and communication within biofilms. This review aims to provide the food industry with a sufficient understanding of multispecies biofilms in food fermentation. Practical Application: Meanwhile, it offers a reference value for better controlling and utilizing biofilms during food fermentation process, and the improvement of the yield, quality, and safety of fermented products including Chinese Baijiu, cheeese,kefir, soy sauce, kombucha, and fermented olive.

Integrated Transcriptome and Proteome Analyses Reveal Protein Metabolism in Lactobacillus helveticus CICC22171

Lactobacillus helveticus is a homofermentative lactic acid bacterium. It is widely used in the fabrication of Swiss cheese and other dairy products. The aim of this study was to elucidate the mechanism by which L. helveticus utilizes protein. Lactobacillus helveticus CICC22171 were cultured in two different media with various nitrogen sources. The control contained 20 basic amino acids, while the experimental medium contained casein. De novo transcriptome and isobaric tags for relative and absolute quantification (iTRAQ) proteome analyses were applied to determine how L. helveticus utilizes protein. The casein underwent extracellular hydrolysis via ATP-binding cassette (ABC) transporter upregulation and Mn²⁺-associated cell envelope proteinase (CEP) downregulation. Sigma factors and EF-Tu were upregulated and Mg²⁺ was reduced in bacteria to accommodate DNA transcription and protein translation in preparation for proteolysis. Hydrolase activity was upregulated to digest intracellular polypeptides and control endopeptidase genes. In these bacteria, casein utilization affected glycolysis, trehalose phosphotransferase system (PTS), and key factors associated with aerobic respiration and reduced glucose consumption.

Mechanisms for Induction of Microbial Extracellular Proteases in Response to Exterior Proteins

Proteins are a main organic nitrogen source for microorganisms. Many heterotrophic microorganisms secrete extracellular proteases (ex-proteases) to efficiently decompose proteins into oligopeptides and amino acids when exterior proteins are required for growth. These ex-proteases not only play important roles in microbial nutrient acquisition or host infection but also contribute greatly to the global recycling of carbon and nitrogen. Moreover, may microbial ex-proteases have important applications in industrial, medical, and biotechnological areas. Therefore, uncovering the mechanisms by which microorganisms initiate the expression of ex-protease genes in response to exterior proteins is of great significance. In this review, the progress made in understanding the induction mechanisms of microbial ex-proteases in response to exterior proteins is summarized, with a focus on the inducer molecules, membrane sensors, and downstream pathways. Problems to be solved for better understanding of the induction mechanisms of microbial ex-proteases are also discussed.