Salt-stress-responsive membrane proteins in Rhodobacter sphaeroides f. sp denitrificans IL106

The salt-mediated-stress response in Rhodobacter sphaeroides f. sp. denitri ficans IL 106 was Investigated by culturing cells in the presence and in th e absence of NaCl in growth media. Fractionation of cells followed by SDS-P AGE and 2D-PAGE revealed an increase in the levels of membrane proteins of 39 and 50 kDa and a decrease in the level of a membrane protein of 52 kDa w ith increasing levels of external NaCl. The proteins were isolated and sequ enced. The polypeptide of 50 kDa in the inner membrane was assigned to an A TP synthase beta chain and that of 52 kDa in the outer membrane to a flagel lar filament protein. As the N terminal of the 39 kDa protein in the outer membrane was blocked, partial proteolysis was carried out and four peptides were sequenced. Each sequence exhibited no significant homology with those available in databases, suggesting that the polypeptide of 39 kDa (named S spA) is a novel salt-stress-induced protein.