Induction of the heat shock protein ClpB affects cold acclimation in the cyanobacterium Synechococcus sp. strain PCC 7942

Abstract

The heat shock protein ClpB is essential for acquired thermotolerance in cyanobacteria and eukaryotes and belongs to a diverse group of polypeptides which function as molecular chaperones. In this study we show that ClpB is also strongly induced during moderate cold stress in the unicellular cyanobacterium Synechococcus sp. strain PCC 7942. A fivefold increase in ClpB (92 kDa) content occurred when cells were acclimated to 25°C over 24 h after being shifted from the optimal growth temperature of 37°C. A corresponding increase occurred for the smaller ClpB (78 kDa), which arises from a second translational start within the clpB gene of prokaryotes. Shifts to more extreme cold (i.e., 20 and 15°C) progressively decreased the level of ClpB induction, presumably due to retardation of protein synthesis within this relatively cold-sensitive strain. Inactivation of clpB in Synechococcus sp. increased the extent of inhibition of photosynthesis upon the shift to 25°C and markedly reduced the mutant's ability to acclimate to the new temperature regime, with a threefold drop in growth rate. Furthermore, around 30% fewer ⌬clpB cells survived the shift to 25°C after 24 h compared to the wild type, and more of the mutant cells were also arrested during cell division at 25°C, remaining attached after septum formation. Development of a cold thermotolerance assay based on cell survival clearly demonstrated that wild-type cells could acquire substantial resistance to the nonpermissive temperature of 15°C by being pre-exposed to 25°C. The same level of cold thermotolerance, however, occurred in the ⌬clpB strain, indicating ClpB induction is not necessary for this form of thermal resistance in Synechococcus spp. Overall, our results demonstrate that the induction of ClpB contributes significantly to the acclimation process of cyanobacteria to permissive low temperatures.

Effects of high light on transcripts of stress-associated genes for the cyanobacteria Synechocystis sp. PCC 6803 and Prochlorococcus MED4 and MIT9313

“…In the present study, clpB1 transcripts transiently increased while clpB2 mRNA levels did not change following the transfer to HL (Tables 3-5). ClpB1 was shown to be essential for resistance to highand low-temperature stress in Synechococcus elongatus Porankiewicz & Clarke, 1997). While ClpB2 has been suggested to be an essential constitutive protein with general chaperone activity (Eriksson et al, 2001), our data indicate that ClpB1 might have a stress-related function.…”

clpB, a Novel Member of theListeria monocytogenesCtsR Regulon, Is Involved in Virulence but Not in General Stress Tolerance

“…A recent study reports the induction of L. monocytogenes clpB during growth at low temperature (36), a condition which seems to induce the activity of most of the general stress proteins; for the cyanobacterium Synechococcus sp., ClpB was shown to be involved in cold adaptation (49). Growth at low temperature is an important part of the L. monocytogenes life cycle and is one which favors food contamination and outbreaks of food-borne disease.…”

Identification of a gene, ccr-1 (sll1242), required for chill-light tolerance and growth at 15 °C in Synechocystis sp. PCC 6803

“…Heat-shock proteins ClpB, ClpP1, HtpG and GroEL are required for cold tolerance and/or are upregulated at low temperature (Porankiewicz & Clarke, 1997;Porankiewicz et al, 1998;Hossain & Nakamoto, 2002). Transcripts and/or proteins encoded by rbp (RNA-binding protein) (Sato, 1995), crhC (RNA helicase) (Chamot et al, 1999;Chamot & Owttrim, 2000) and btpA (required for stabilization of photosystem I, PSI) (Zak & Pakrasi, 2000) accumulate at low temperature in cyanobacteria.…”