Abstract
Toxin-antitoxin (TA) systems are widely distributed in bacterial genomes and are involved in the adaptive response of microorganisms to stress conditions. Few studies have addressed TA systems in Lactobacillus and their role in the adaptation to food environments and processes. In this work, for six strains belonging to L. casei group isolated from dairy products, the expression of DinJ-YafQ TA system was investigated after exposure to various food-related stresses (nutrient starvation, low pH, high salt concentration, oxidative stress, and high temperature), as well as to the presence of antibiotics. In particular, culturability and DinJ-YafQ expression were evaluated for all strains and conditions by plate counts and RT qPCR. Among all the food-related stress conditions, only thermal stress was capable to significantly affect culturability. Furthermore, exposure to ampicillin significantly decreased the culturability of two L. rhamnosus strains. The regulation of DinJ-YafQ TA system resulted strain-specific; however, high temperature was the most significant stress condition able to modulate DinJ-YafQ expression. The increasing knowledge about TA systems activity and regulation might offer new perspectives to understand the mechanisms that L. casei group strains exploit to adapt to different niches or production processes.
Highlights
Toxin-antitoxin (TA) are systems encoded by two neighbouring genes widely distributed in the genomes of bacteria and archea, involved in the management of adaptive response of microorganisms by regulating cell growth and death as a result of stress conditions
The type I TA locus identified in plasmid DNA of dairy L. rhamnosus isolates, is characterized by a mRNA encoding for the toxin peptide (Lpt) and a non-coding RNA acting as antitoxin convergently transcribed [13]
This phenomenon has been observed for L. casei group in response to raw-milk cheese manufacturing process characterized by technological parameters inducing a selective pressure [18]
Summary
Toxin-antitoxin (TA) are systems encoded by two neighbouring genes widely distributed in the genomes of bacteria and archea, involved in the management of adaptive response of microorganisms by regulating cell growth and death as a result of stress conditions. The species L. casei, L. paracasei and L. rhamnosus, commonly defined as L. casei group due to their phylogenetic relatedness, are associated with a variety of environments, such as raw and fermented dairy products, fermented vegetables and gut microbiota of vertebrates [5] Their ubiquity in diverse environments is due to their metabolic flexibility [6], such as the aptitude to ferment different substrates [7,8], and to their capability to cope with environmental stress conditions commonly encountered in their niches, such as food environment [9,10] and human gastrointestinal tract. The initial bacterial load is low and increases during the ripening despite the unfavourable growth environment
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