Deciphering the Antitoxin-Regulated Bacterial Stress Response via Single-Cell Analysis.

Bacterial toxin-antitoxin (TA) systems, which are diverse and widespread among prokaryotes, are responsible for tolerance to drugs and environmental stresses. However, the low abundance of toxin and antitoxin proteins renders their quantitative measurement in single bacteria challenging. Employing a laboratory-built nano-flow cytometer (nFCM) to monitor a tetracysteine (TC)-tagged TA system labeled with the biarsenical dye FlAsH, we here report the development of a sensitive method that enables the detection of basal-level expression of antitoxin. Using the Escherichia coli MqsR/MqsA as a model TA system, we reveal for the first time that under its native promoter and in the absence of environmental stress, there exist two populations of bacteria with high or low levels of antitoxin MqsA. Under environmental stress, such as bile acid stress, heat shock, and amino acid starvation, the two populations of bacteria responded differently in terms of MqsA degradation and production. Subsequently, resumed production of MqsA after amino acid stress was observed for the first time. Taking advantage of the multiparameter capability of nFCM, bacterial growth rate and MqsA production were analyzed simultaneously. We found that under environmental stress, the response of bacterial growth was consistent with MqsA production but with an approximate 60 min lag. Overall, the results of the present study indicate that stochastic elevation of MqsA level facilitates bacterial survival, and the two populations with distinct phenotypes empower bacteria to deal with fluctuating environments. This analytical method will help researchers gain deeper insight into the heterogeneity and fundamental role of TA systems.

Relationship Between Quorum Sensing and Secretion Systems.

Quorum sensing (QS) is a communication mechanism between bacteria that allows specific processes to be controlled, such as biofilm formation, virulence factor expression, production of secondary metabolites and stress adaptation mechanisms such as bacterial competition systems including secretion systems (SS). These SS have an important role in bacterial communication. SS are ubiquitous; they are present in both Gram-negative and Gram-positive bacteria and in Mycobacterium sp. To date, 8 types of SS have been described (T1SS, T2SS, T3SS, T4SS, T5SS, T6SS, T7SS, and T9SS). They have global functions such as the transport of proteases, lipases, adhesins, heme-binding proteins, and amidases, and specific functions such as the synthesis of proteins in host cells, adaptation to the environment, the secretion of effectors to establish an infectious niche, transfer, absorption and release of DNA, translocation of effector proteins or DNA and autotransporter secretion. All of these functions can contribute to virulence and pathogenesis. In this review, we describe the known types of SS and discuss the ones that have been shown to be regulated by QS. Due to the large amount of information about this topic in some pathogens, we focus mainly on Pseudomonas aeruginosa and Vibrio spp.