Analysis of a new defense mechanism against microbial infections found in Paramecium

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Once Paramecium caudatum has been infected by endosymbiotic bacterium Holospora obtusa, the host cells become reduced the ability for digestive vacuole formation to the secondary added same bacteria, and that this change in the vacuole formation is induced within 4 h after the first infection. H. obtusa-bearing host cells can ingest various bacteria if the host has not yet been infected before by them. These suggest that Paramecium can distinguish and memory the infectious Holospora and acquires an unknown defense mechanism for the secondary infection. Treatment of the secondary added infectious H. obtusa with Lipase, Proteinase K, Lyticase, alpha-mannnosidase, or beta-galactosidase did not affect the host digestive vacuole formation. Also, treatments of the secondary added infectious H. obtusa and the host with antibodies for a 250-kDa cell surface protein of aposymbiotic paramecia are not effective. This phenomenon is repeatable, but molecular mechanism is still unknown.