bis(3--5-)-cyclic-diguanylic-acid and Hypoxia

During infection, intracellular pathogens inevitably face the pressure of hypoxia. Mycobacterium tuberculosis and Mycobacterium bovis represent two typical intracellular bacteria, but the signalling pathway of their adaptation to hypoxia remains unclear. Here, we report a new mechanism of the hypoxic adaptation in M. bovis driven by the second messenger molecule c-di-GMP. We found that c-di-GMP was significantly accumulated in bacterial cells under hypoxic stress and blocked the inhibitory activity of ArgR, an arginine metabolism gene cluster regulator, which increased arginine synthesis and slowed tricarboxylic acid cycle (TCA cycle) and aerobic respiration. Meanwhile, c-di-GMP relieved the self-inhibition of argR expression, and ArgR could interact with the nitrite metabolic gene regulator Cmr, promoting the positive regulation of Cmr and, thereafter, the nitrite respiration. Consistently, c-di-GMP significantly induced the expression of arginine and nitrite metabolism gene clusters and increased the mycobacterial survival ability under hypoxia. Therefore, we found a new function of the second messenger molecule c-di-GMP and characterized ArgR as a metabolic switching regulator that can coordinate the c-di-GMP signal to trigger hypoxic adaptation in mycobacteria. Our findings provide a potential new target for blocking the life cycle of M. tuberculosis infection.

Topics: Arginine; Bacterial Proteins; Cyclic GMP; Gene Expression Regulation, Bacterial; Humans; Hypoxia; Mycobacterium bovis; Mycobacterium tuberculosis; Nitrites

Pseudomonas aeruginosa encodes many enzymes that are potentially associated with the synthesis or degradation of the widely conserved second messenger cyclic-di-GMP (c-di-GMP). In this study, we show that mutation of rbdA, which encodes a fusion protein consisting of PAS-PAC-GGDEF-EAL multidomains, results in decreased biofilm dispersal. RbdA contains a highly conserved GGDEF domain and EAL domain, which are involved in the synthesis and degradation of c-di-GMP, respectively. However, in vivo and in vitro analyses show that the full-length RbdA protein only displays phosphodiesterase activity, causing c-di-GMP degradation. Further analysis reveals that the GGDEF domain of RbdA plays a role in activating the phosphodiesterase activity of the EAL domain in the presence of GTP. Moreover, we show that deletion of the PAS domain or substitution of the key residues implicated in sensing low-oxygen stress abrogates the functionality of RbdA. Subsequent study showed that RbdA is involved in positive regulation of bacterial motility and production of rhamnolipids, which are associated with biofilm dispersal, and in negative regulation of production of exopolysaccharides, which are required for biofilm formation. These data indicate that the c-di-GMP-degrading regulatory protein RbdA promotes biofilm dispersal through its two-pronged effects on biofilm development, i.e., downregulating biofilm formation and upregulating production of the factors associated with biofilm dispersal.

Topics: Biofilms; Cyclic GMP; Gene Expression Regulation, Bacterial; Glycolipids; Guanosine Triphosphate; Hydrolysis; Hypoxia; Locomotion; Phosphoric Diester Hydrolases; Polysaccharides, Bacterial; Protein Structure, Tertiary; Pseudomonas aeruginosa