Abstract: To date, bacterial,algal and other microbial symbionts have been found in more than 100 species of ciliates. The study of the host-symbiont system in ciliates shows that: (1) The inheritance of kappa particles in the cytoplasm of Paramecium aurelia is a classic example of the cytoplasmic inheritance theory. (2)Bacterial symbionts in some anerobic ciliates that lack mitochondria play the major role in the host's metabolism. (3) In the P. caudatum Holospora obtusa system, 39-and 15-kDa periplasmic proteins of the infectious H. obtusa reacted with IF-3-1 and IF-3-2 monoclonal antibodies respectively. The amounts of both antigens were reduced during the early infection process. The reproductive H. obtusa selectively synthesized a 63-kDa protein, which may function as a key molecules in the various symbiotic systems. (4) In the P. bursaria Chlorella system, the precondition of the symbiosis may be the gluosamine composition that exists in the rigid wall of the algae. The symbiotic algae takes part in the host's metabolism, and the specific association between the symbiont and host is mutually beneficial. Some genomic structures in P. bursaria may be influenced by the function of the Chlorella,so that the host's gene expression may change.A general trend in the research of symbiosis in ciliates is further exploration of the influence of the symbiont on the gene structure and gene expression of the host. The expected results will contribute to a better understanding of the regulatory mechanisms controlling the interaction,the exchange of substances between the host and symbiont at a molecular level, and the pattern of life processes surrounding the relationship between cellular structures and functions in eukaryocytes.

Key words: Qilian, butterfly, habitat types, diversity