Genetic and phenotypic characterization of the heat shock response in Pseudomonas putida.
Bottom Line: Molecular chaperones function in various important physiological processes.Null mutants of genes for the molecular chaperone ClpB (Hsp104), and those that encode J-domain proteins (DnaJ, CbpA, and DjlA), which may act as Hsp40 co-chaperones of DnaK (Hsp70), were constructed from Pseudomonas putida KT2442 (KT) to elucidate their roles.P. putida CbpA, a probable Hsp, partially substituted the functions of DnaJ in cell growth and solubilization of thermo-mediated protein aggregates, and might be involved in the HSR which was regulated by a fine-tuning system(s) that could sense subtle changes in the ambient temperature and control the levels of σ(32) activity and quantity, as well as the mRNA levels of hsp genes.
Affiliation: Graduate School of Life Sciences, Toyo University, Gunma.Show MeSH
Related in: MedlinePlus
Mentions: Pseudomonas putida is a ubiquitous Gram-negative bacterium that is metabolically versatile and can adapt to various environmental conditions (Timmis 2002). The strain has a relatively high intrinsic resistance to organic solvents, and a number of factors are known to be involved in the resistance ability (Ramos et al. 2002). In a previous work, we described the toluene-resistant strain of P. putida KT2442 (KT) that accumulated several Hsps under non-stress conditions. A point mutation in dnaK was shown to be the cause of the characteristic phenotypes; namely, toluene resistance, temperature sensitivity, and Hsp accumulation (Kobayashi et al. 2011). Meanwhile, a dnaK insertion mutant isolated from another P. putida strain showed growth retardation at 35°C (Dubern et al. 2005). Although the bacterial HSR has been thoroughly investigated in E. coli; there are not many reports that systematically describe the HSR in the genus Pseudomonas (Allan et al. 1988; Keith et al. 1999; Zhao et al. 2007). Since E. coli and P. putida show notable differences in the control mechanisms for a minor sigma factor, σS (Venturi 2003), the HSR mediated by the heat shock minor sigma factor, σ32, which is encoded by the rpoH gene, in P. putida may be different than that in E. coli. Three J-domain family proteins (i.e., DnaJ, CbpA, and DjlA, encoded by PP4726, PP4848, and PP0407, respectively), each of which may act as a co-chaperone of DnaK, have already been annotated in the genome of P. putida KT2440 (Fig. 2). Our data suggest that the HSR in P. putida is controlled by a system quite similar to that in E. coli; however, curved-DNA-binding protein CbpA, which is controlled by σS in E. coli, is a σ32-dependent Hsp in P. putida, and hence acts as a replacement when DnaJ is depleted. Additionally, our data indicate that posttranscriptional controls of clpB, dnaK, and htpG can be distinct from that of groEL in the strain.
Affiliation: Graduate School of Life Sciences, Toyo University, Gunma.