Abstract:  A large number of flagellates live in the intestine of lower termites, which is vital for the survival of host termites. Different species of flagellates form a food digestion system to provide nutrients and energy for the host. Studies on the community structure of flagellates will provide the basis for elucidating the physiological functions of each member. Species identification based on morphological characteristics is influenced by the flagellate growth and developmental stages, sample preparation methods and other factors, but molecular biological methods based on molecular markers can avoid these drawbacks in studying complex microbial communities. In this study, the community structure of flagellates in the gut of Coptotermes formosanus was investigated with molecular biological methods combining with morphological characteristics. Three methods were also compared in studying community structure. Three species of flagellates (Pseudotrichonympha grassii, Holomastigotoides mirabile, and Spirotrichonympha leidyi) were identified by optical and scanning electron microscopic observation. Compared with morphological identification, 18S rDNA restriction fragment length polymorphism analysis can reveal more species diversity. Cell counting under optical microscopy is more accurate than 18S rDNA analysis in investigating the amount of each flagellate. The average number of flagellates per termite worker was 780±179 for P. grassii, 1 630±391 for H. mirabile, and 2 950±1 003 for Spirotrichonympha leidyi. This study established a method of combining optical microscopy observation with 18S rDNA analysis to investigate intestinal flagellate community, which is the foundation to clarify the biological functions of the gut symbionts.

Key words: Flagellate; Coptotermes formosanus, community structure, morphological identification, molecular marker, 18S rDNA, RFLP