Impacts of type II toxin-antitoxin systems on cell physiology and environmental behavior in acetic acid bacteria

Regulatory mechanisms of acetic acid, ethanol and high temperature tolerances of acetic acid bacteria during vinegar production

Acetic acid bacteria (AAB) play a pivotal role in the food fermentation industry, especially in vinegar production, due to their ability to partially oxidize alcohols to acetic acid. However, economic bioproduction using AAB is challenged by harsh environments during acetic acid fermentation, among which initial ethanol pressure, subsequent acetic acid pressure, and consistently high temperatures are common experiences. Understanding the stress-responsive mechanisms is essential to developing robust AAB strains. Here, we review recent progress in mechanisms underlying AAB stress response, including changes in cell membrane composition, increased activity of membrane-bound enzymes, activation of efflux systems, and the upregulation of stress response molecular chaperones. We also discuss the potential of advanced technologies, such as global transcription machinery engineering (gTME) and Design-Build-Test-Learn (DBTL) approach, to enhance the stress tolerance of AAB, aiming to improve vinegar production.

Comparative analysis of five type II TA systems identified in Pseudomonas aeruginosa reveals their contributions to persistence and intracellular survival

Background

Pseudomonas aeruginosa is a grave nosocomial pathogen that persistently inhabits the lungs of patients with cystic fibrosis (CF) and causes various chronic infections. The bacterial toxin-antitoxin (TA) system is associated with latent and long-term infections, but the underlying mechanisms remain to be fully characterized.

Methods

We here investigated the diversity and function of five genomic type II TA systems widely distributed among P. aeruginosa clinical isolates. We also examined the distinct structural features of the toxin protein from different TA systems and characterized their contributions to persistence, invasion ability, and intracellular infection caused by P. aeruginosa.

Results

ParDE, PA1030/PA1029, and HigBA could modulate persister cell formation under treatment with specific antibiotics. Furthermore, cell-based transcriptional and invasion assays revealed that PA1030/PA1029 and HigBA TA systems were critical for intracellular survival.

Discussion

Our results highlight the prevalence and diverse roles of type II TA systems in P. aeruginosa and evaluate the possibility of using PA1030/PA1029 and HigBA TA pairs as targets for novel antibiotic treatments.

Structural insights into the PrpTA toxin-antitoxin system in Pseudoalteromonas rubra

Bacteria could survive stresses by a poorly understood mechanism that contributes to the emergence of bacterial persisters exhibiting multidrug tolerance (MDT). Recently, Pseudoalteromonas rubra prpAT module was found to encode a toxin PrpT and corresponding cognate antidote PrpA. In this study, we first reported multiple individual and complex structures of PrpA and PrpT, which uncovered the high-resolution three-dimensional structure of the PrpT:PrpA2:PrpT heterotetramer with the aid of size exclusion chromatography-multi-angle light scattering experiments (SEC-MALS). PrpT:PrpA2:PrpT is composed of a PrpA homodimer and two PrpT monomers which are relatively isolated from each other and from ParE family. The superposition of antitoxin monomer structures from these structures highlighted the flexible C-terminal domain (CTD). A striking conformational change in the CTDs of PrpA homodimer depolymerized from homotetramer was provoked upon PrpT binding, which accounts for the unique PrpT-PrpARHH mutual interactions and further neutralizes the toxin PrpT. PrpA2-54-form I and II crystal structures both contain a doughnut-shaped hexadecamer formed by eight homodimers organized in a cogwheel-like form via inter-dimer interface dominated by salt bridges and hydrogen bonds. Moreover, PrpA tends to exist in solution as a homodimer other than a homotetramer (SEC-MALS) in the absence of flexible CTD. Multiple multi-dimers, tetramer and hexamer included, of PrpA2-54 mediated by the symmetric homodimer interface and the complicated inter-dimer interface could be observed in the solution. SEC-MALS assays highlighted that phosphate buffer (PB) and the increase in the concentration appear to be favorable for the PrpA2-54 oligomerization in the solution. Taken together with previous research, a model of PrpA2-54 homotetramer in complex with prpAT promoter and the improved mechanism underlying how PrpTA controls the plasmid replication were proposed here.

Comprehensive deciphering prophages in genus Acetobacter on the ecology, genomic features, toxin–antitoxin system, and linkage with CRISPR-Cas system

Acetobacter is the predominant microbe in vinegar production, particularly in those natural fermentations that are achieved by complex microbial communities. Co-evolution of prophages with Acetobacter, including integration, release, and dissemination, heavily affects the genome stability and production performance of industrial strains. However, little has been discussed yet about prophages in Acetobacter. Here, prophage prediction analysis using 148 available genomes from 34 Acetobacter species was carried out. In addition, the type II toxin–antitoxin systems (TAs) and CRISPR-Cas systems encoded by prophages or the chromosome were analyzed. Totally, 12,000 prophage fragments were found, of which 350 putatively active prophages were identified in 86.5% of the selected genomes. Most of the active prophages (83.4%) belonged to the order Caudovirales dominated by the families Siphoviridae and Myroviridae prophages (71.4%). Notably, Acetobacter strains survived in complex environments that frequently carried multiple prophages compared with that in restricted habits. Acetobacter prophages showed high genome diversity and horizontal gene transfer across different bacterial species by genomic feature characterization, average nucleotide identity (ANI), and gene structure visualization analyses. About 31.14% of prophages carry type II TAS, suggesting its important role in addiction, bacterial defense, and growth-associated bioprocesses to prophages and hosts. Intriguingly, the genes coding for Cse1, Cse2, Cse3, Cse4, and Cas5e involved in type I-E and Csy4 involved in type I-F CRISPR arrays were firstly found in two prophages. Type II-C CRISPR-Cas system existed only in Acetobacter aceti, while the other Acetobacter species harbored the intact or eroded type I CRISPR-Cas systems. Totally, the results of this study provide fundamental clues for future studies on the role of prophages in the cell physiology and environmental behavior of Acetobacter.