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SigC sigma factor is involved in acclimation to low inorganic carbon at high temperature in Synechocystis sp. PCC 6803

Maija Pollari

Virpi Ruotsalainen

Plant Physiology and Molecular Biology, Department of Biology, University of Turku, FI-20014 Turku, Finland

Inactivation of the sigC gene (sll0184), encoding the group 2 sigma factor SigC, leads to a heat-sensitive phenotype of Synechocystis sp. PCC 6803. Cells of the sigC strain grew poorly at 43 °C at pH 7.5 under ambient CO₂ conditions. Addition of inorganic carbon in the form of 3 % CO₂ or use of an alkaline growth medium (pH 8.3) restored the growth of the sigC strain at 43 °C. These treatments compensate for the low concentration of inorganic carbon at high temperature. However, addition of organic carbon as glucose, pyruvate, succinate or 2-oxoglutarate did not restore growth of the sigC strain at 43 °C. In the control strain, the amount of the SigC factor diminished after prolonged incubation at 43 °C if the pH of the growth medium was 7.5 or 6.7. Under alkaline conditions, the amount of the SigC factor remained constant at 43 °C and cells of the control strain grew better than at pH 7.5 or pH 6.7. The pH dependence of high-temperature growth was associated with changes in photosynthetic activity, indicating that the SigC factor is involved in adjustment of photosynthesis according to the amount of available inorganic carbon. Our results indicate that acclimation to low inorganic carbon is a part of acclimation to prolonged high temperature and that the SigC factor has a central role in this acclimation.

Correspondence
Taina Tyystjärvi
taityy{at}utu.fi

Present address: VTT Technical Research Centre of Finland, FI-02044 Espoo, Finland.

Present address: Faculty of Biosciences, Natural Product Research Laboratories, University of Joensuu, FI-80101 Joensuu, Finland.