QUANTITATIVE CHANGES IN PERIPLASMIC PROTEINS OF THE MACRONUCLEUS-SPECIFIC BACTERIUM HOLOSPORA-OBTUSA IN THE INFECTION PROCESS OF THE CILIATE PARAMECIUM-CAUDATUM

The Gram-negative bacterium Holospora obtusa is a macronucleus-specifi c symbiont of the ciliate Paramecium caudatum. The infectious form of this bacterium infects the host macronucleus through digestive vacuole s and differentiates into the reproductive form two days after the inf ection in the nucleus. The monoclonal antibodies IF-3-1 and IF-3-2 rea cted with 39 and 15 kDa periplasmic proteins, respectively, that were specific for the infectious form of H. obtusa. Because the antigens we re not detected in the reproductive form of the bacterium, it appears that expression of the proteins decreases during or soon after the inf ection. Using these antibodies, quantitative changes in the antigens i n the early infection process were examined by immunoblotting and immu nogold electron microscopy. Immunoblotting showed that the amounts of both antigens were reduced within 1 h after the bacteria were engulfed into the digestive vacuoles of the paramecia, but that the amounts of IF-3-2 antigens declined earlier than the IF-3-1 antigen. Immunogold labeling showed that the level of IF-3-2 antigens became very low in t he bacteria in the host digestive vacuoles, whereas there was no simil ar decrease in amount of IF-3-1 antigens. Possible functions of the an tigens are discussed. The IF-3-1 antigens decrease in concentration in parallel with the decrease in the periplasmic region.