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Replicase
Published in Paul Pumpens, Single-Stranded RNA Phages, 2020
Concerning hexamer to monomer equilibrium of the E. coli Hfq, Panja and Woodson (2012) found that the Hfq underwent a cooperative conformational change from monomer to hexamer around 1 μM protein, which was comparable to the in vivo concentration of the Hfq and above the dissociation constant of the Hfq hexamer from many RNA substrates. Above 2 μM protein, the Hfq hexamers associated in high-molecular-mass complexes. It was shown clearly that the Hfq was most active in RNA annealing when the hexamer was present. Selective 2′-hydroxyl acylation and primer extension, small-angle x-ray scattering, and Monte Carlo molecular dynamics simulations were applied to build up a low-resolution model of E. coli Hfq bound to the rpoS mRNA, a bacterial stress response gene that is targeted by three different sRNAs (Peng Y et al. 2014). Next, the ESI-MS analyses were used to characterize the native E. coli Hfq obtained through methods that preserved its posttranslational modifications (Obregon et al. 2015). This approach showed that the majority of the cellular Hfq cannot be extracted without detergents, and that purified Hfq can be retained on hydrophobic matrices. Analyses of the purified Hfq and the native Hfq complexes observed in whole-cell E. coli extracts indicated the existence of dodecameric assemblies likely stabilized by interlocking C-terminal polypeptides originating from separate Hfq hexamers and/or accessory nucleic acid. The cellular Hfq was redistributed between transcription complexes and an insoluble fraction that included protein complexes harboring polynucleotide phosphorylase. This distribution pattern was consistent with a function at the interface of the apparatuses responsible for the RNA synthesis and degradation. It was concluded that the Hfq functions as an anchor/coupling factor responsible for de-solubilization of RNA, and it is tethered to the degradosome complex (Obregon et al. 2015). Zheng et al. (2016) compared the RNA binding and RNA annealing activities of the Hfq from E. coli, P. aeruginosa, Listeria monocytogenes, B. subtilis, and S. aureus using minimal RNAs and fluorescence spectroscopy, and concluded that the RNA annealing activity increased with the number of arginine residues in a semi-conserved patch on the rim of the Hfq hexamer, and correlated with the previously reported requirement for the Hfq in the sRNA regulation.
Bacterial stress response: understanding the molecular mechanics to identify possible therapeutic targets
Published in Expert Review of Anti-infective Therapy, 2021
Amit Kumar, Anu Rahal, Jagdip Singh Sohal, Vivek Kumar Gupta
Understanding of physical, physiological changes produced by bacterial pathogen in cellular environment with cellular response to bacterial stress like immunomodulation, metabolism, process of cell cycle regulation, differentiation, and xenophagy adjudicate a better way for the selection of effective and successful selection of therapeutics for desired targets [20]. However, still more precise and comprehensive knowledge is required to understand many pathways involved in the bacterial stress response and its arbitration. Many of the pathways discussed are proposed one and yet to be established so before the recommendation or use of any therapeutic to alter any component of bacterial stress management system utmost care should be taken to avoid any untoward or undesired side effects.
Deletion of the lon gene augments expression of Salmonella Pathogenicity Island (SPI)-1 and metal ion uptake genes leading to the accumulation of bactericidal hydroxyl radicals and host pro-inflammatory cytokine-mediated rapid intracellular clearance
Published in Gut Microbes, 2020
Perumalraja Kirthika, Amal Senevirathne, Vijayakumar Jawalagatti, SungWoo Park, John Hwa Lee
The generation of reactive oxygen species (ROS) is a hallmark of the bacterial stress response. In bacteria, ROS are readily detoxified by enzymatic conversion of ROS (OH·) into hydrogen peroxide and subsequently to water and oxygen. However, in the presence of iron ions, the Fenton reaction can generate OH· that are lethal to bacterial cells.21 To elucidate the kinetics of OH· generation in JOL 401, JOL909, and JOL909::lon, cells were exposed to various naturally-occurring stress conditions for 5 h. JOL 401 was able to effectively mitigate OH· generation under cold and oxidative stress; however, the production of OH· was significantly higher under osmotic and acidic pH conditions. Under all stress conditions, JOL 909 appeared to have produced higher levels of OH·. The maximum level of OH· production in JOL 909 was observed under oxidative stress, suggesting the role of Lon protease in mitigating oxidative stress. The involvement of Lon seems to be comparatively less with osmotic and acidic stress conditions. The results were corroborated with JOL 909::lon, which effectively diminished OH· production. These results imply the critical involvement of Lon protease activity in mitigating oxidative stress in the phagosomes of host cells22 (Figure 3). It is worthwhile to note that JOL 909::lon exhibited lower levels of OH· compared to JOL 401. As the overproduction of Lon can prove fatal for bacterial cells, these low levels may be due to slightly higher levels of Lon protein in JOL 909 complemented in trans by a low-copy-number plasmid.
Investigation of the population dynamics within a Pseudomonas aeruginosa biofilm using a flow based biofilm model system and flow cytometric evaluation of cellular physiology
Published in Biofouling, 2018
Juzwa Wojciech, Myszka Kamila, Białas Wojciech
The percentages of the defined sub-populations supported the conclusion that the biofilm and planktonic forms of P. aeruginosa cells followed different physiological patterns in response to differences in the nutrients availability. This was observed for both the initial adhesion and the biofilm maturation stage vs corresponding samples of suspended cells. The more complex structure of P. aeruginosa population within a biofilm may occur due to generation of genetic diversity, as demonstrated in the number of reports on biofilm-derived cells. Many research groups found that bacterial growth within a biofilm can produce diverse genetic variants, even though no external stress or mutagen is applied. This was demonstrated for biofilms of Pseudomonas aeruginosa, Pseudomonas fluorescence, Vibrio cholerae, Streptococcus pneumoniae and Staphylococcus aureus (Boles et al. 2004; Kirisits et al. 2005; Allegrucci and Sauer 2007; Palmer and Stoodley 2007; Yarwood et al. 2007). The microbial cells forming a biofilm structure acquire the increased resistance to adverse conditions by inducing phenotypes that are not likely to occur among planktonically grown cells. The biofilm environment itself may induce bacterial stress response triggering hypermutability. The diverse sub-populations generated in this way result in the potential of the microbial community to thrive in a range of conditions (Moxon et al. 1994; Foster 1995; Chung et al. 2006; Boles and Singh 2008). The biofilm-mediated diversity within microbial communities originates from strong and varied selective pressure related to: (1) many microenvironments (chemical gradients and transport limitations) with differing conditions occurring within a spatial biofilm structure (Rasmussen and Lewandowski 1998; Teal et al. 2006); and (2) physical separation of the cells occupying different biofilm regions – geographic isolation leads to different bacterial lineages, which undergo different paths of evolution (Boles and Singh 2008). Even subtle genetic differences may result in phenotypic and morphotypic transformations, leading to emergence of microbial variants that differ substantially in biofilm formation abilities and expression of biofilm-related genes (Dragoš et al. 2017). This biofilm-related diversity of microbial cells may explain both the more complex structure of P. aeruginosa population observed for biofilm forms and the lower percentages of active cells compared to free-living cells.