Analysis of Stress Responsive Gene for Salinity in a Marine Cyanobacterium Synechococcus sp

Abstract

There are many stress conditions in natural environment where organisms have been developed their physiological functions to adapt to these conditions. Marine organisms have several strategies for adapting osmotic stress. We have screened many useful marine photosynthetic microorganisms from several oceanic area and found a unique marine cyanobacterium Synechococcus sp. NKBG042902 (Matsunaga et al., 1990) which grows under wide salinity range of 0–5% NaCI and quickly adapts to different salinity conditions. The NKBG042902 have an interesting endogenous plasmid, pSY10, which copy number is controlled by salinity conditions (Takeyama et al., 1991). This marine plasmid pSY10 is maintained at high copy number under seawater conditions (including 3% NaCl), whereas its copy number is depressed under fresh water conditions (without NaCl) (Figure 1). The size of this plasmid was determined 2561 bp and repA gene sequence encoding replication protein was found (Kawaguchi et al., 1994). The replication of this plasmid was presumed to be mediated by RepA protein. At upstream region of the repA gene, two promoter regions (Prep1, Prep2) having high similarity to strong promoter of E. coli sigma 70 factor were found. The replication mechanism of pSY10 mediated by RepA protein was elucidated under different salinity conditions.