Bacterial type II toxin-antitoxin systems acting through post-translational modifications.

The post-translational modification (PTM) serves as an important molecular switch mechanism to modulate diverse biological functions in response to specific cues. Though more commonly found in eukaryotic cells, many PTMs have been identified and characterized in bacteria over the past decade, highlighting the importance of PTMs in regulating bacterial physiology. Several bacterial PTM enzymes have been characterized to function as the toxin component of type II TA systems, which consist of a toxin that inhibits cell growth and an antitoxin that protects the cell from poisoning by the toxin. While TA systems can be classified into seven types based on nature of the antitoxin and its activity, type II TA systems are perhaps the most studied among the different TA types and widely distributed in eubacteria and archaea. The type II toxins possessing PTM activities typically modify various cellular targets mostly associated with protein translation and DNA replication. This review mainly focuses on the enzymatic activities, target specificities, antitoxin neutralizing mechanisms of the different families of PTM toxins. We also proposed that TA systems can be conceptually viewed as molecular switches where the 'on' and 'off' state of the system is tightly controlled by antitoxins and discussed the perspective on toxins having other physiologically roles apart from growth inhibition by acting on the nonessential cellular targets.

EmhR is an indole-sensing transcriptional regulator responsible for the indole-induced antibiotic tolerance in Pseudomonas fluorescens.

Indole is well known as an interspecies signalling molecule to modulate bacterial physiology; however, it is not clear how the indole signal is perceived and responded to by plant growth promoting rhizobacteria (PGPR) in the rhizosphere. Here, we demonstrated that indole enhanced the antibiotic tolerance of Pseudomonas fluorescens 2P24, a PGPR well known for its biocontrol capacity. Proteomic analysis revealed that indole influenced the expression of multiple genes including the emhABC operon encoding a major multidrug efflux pump. The expression of emhABC was regulated by a TetR-family transcription factor EmhR, which was demonstrated to be an indole-responsive regulator. Molecular dynamics simulation showed that indole allosterically affected the distance between the two DNA-recognizing helices within the EmhR dimer, leading to diminished EmhR-DNA interaction. It was further revealed the EmhR ortholog in Pseudomonas syringae was also responsible for indole-induced antibiotic tolerance, suggesting this EmhR-dependent, indole-induced antibiotic tolerance is likely to be conserved among Pseudomonas species. Taken together, our results elucidated the molecular mechanism of indole-induced antibiotic tolerance in Pseudomonas species and had important implications on how rhizobacteria sense and respond to indole in the rhizosphere.

rAAV9-UPII-TK-EGFP can precisely transduce a suicide gene and inhibit the growth of bladder tumors.

Bladder cancer is a common and widespread cancer of the human urinary system, and its incidence is increasing. Gene therapy is a promising treatment of bladder cancer. In our study, a recombinant adeno-associated virus (rAAV9-UPII-TK-EGFP) driven by a UPII promoter was constructed. The efficacy and safety of infection of bladder cells was tested in vivo and in vitro. The ability of rAAV9-UPII-TK-EGFP to penetrate the glycosaminoglycan (GAG) layer on the surface of bladder cells and to transduce the bladder cells in vivo was very high. Additionally, we confirmed that the TK/GCV system has a powerful cytotoxic effect on bladder tumor cells in vitro and in vivo. Thus, our data indicate that rAAV9-UPII-TK-EGFP is a precise gene drug delivery system for the treatment of bladder cancer, and the TK/GCV therapeutic strategy has a powerful antitumor effect. These findings can be widely used in clinical and scientific studies.