Lysozyme catalyzes the hidrolysis of the 1, 4-B-gucosidic linkage between N-acetylmuramic acid and N-acetylglucosamine of peptidoglucan present in the cell wall of many bacteria, causing cell lysis. Lysozyme is part of the defense mechanism against bacteria and has been distributed in most animals, including insects. Lysozyme has also implied in the midgut digestion of bacteria by organisms which ingest large amounts of them, or that harbor a bacterial culture in their guts, exemplified by vertebrate foregut fermenters Similarly, among the insects, digesting lysozymes are reported from saprophagous Diptera. These insects lysis bacteria in their food with stomach lysozyme and absorb microbial tissue in the midgut. On the other hand, wood-feeding termites re also oligonitrotrophic, and possibility that how they get enough nitrogen to construct living body is intriguing. We suspected the possibility that termites have digestive lysozyme to utilize their hindgut bacteria as nutrient source. We measured lysozyme and protease activities of enzyme extract prepared from termite tissues. Using amino acid analyzer, we analyzed amino acid composition in the termite guts, and calculated the concentration of total free amino acid in each part of guts. Total activity of lysozyme was found predominantly in salivary gland and to a minor extent in digestive tract. However, high specific activity of lysozyme was detected in foregut as well as in salivary gland. The similarity of lysozyme pH-profile in salivary gland and foregut suggested that foregut lysozyme came from salivary gland. The highest protease activity having the optimum pH 7.5 was found in midgut. Total amino acid content and concentration of midgut ware higher than foregut and hindgut. From these results, the possibility that lysozyme secreted from salivary gland to foregut digest the symbiont bacteria transferred by trophallaxis of the termite for use of nitrogen source is suggested. Provided that termites utilized their hindgut bacteria, it would be reasonable for them to ingest gut bacteria through proctodeal trophallaxis and lysis them in their foreguts, because their fermentative tissue is hindgut. Although, Breznak suspected the possibility of nutritive potential of bacterial cell material through trophallaxis in termites, there has been no study on this problem. In this study, we observed the behavior of R. speratus, and indicate termites digest a part of hindgut bacteria as nitrogen resource through proctodeal trophallaxis in the enzymologic way.

Index terms: Reticulitermes speratus, Lysozyme, Trophallaxis, Nitrogen Metabolism

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