Dual origin of gut proteases in Formosan subterranean termites (Isoptera: Rhinotermitidae)

Cellulose digestion in lower termites mediated by carbohydrases originating from both termite and endosymbionts is well characterized. In contrast, limited information exists on lower termite gut proteases, their origins and roles in termite nutrition. The objective of this study was therefore to characterize gut proteases of lower termites. The protease activity of lysates from gut tissues (fore, mid and hindgut) and protozoa isolated from hindgut of worker Formosan subterranean termites (Coptotermes formosanus Shiraki) was assayed using hide powder azure and analyzed by zymogram using gelatin sodium dodecylsulfate-polyacrylamide gel electrophoresis (gelatin SDS-PAGE). Midgut tissue lysates showed the highest protease activity followed by the protozoa lysates. High level of protease activity was also detected in protozoa lysates and culture supernatants after a 24 h incubation of the protozoa in Trager U saline. Incubation of gut and protozoa lysates with class-specific protease inhibitors revealed the presence of serine proteases. All proteolytic bands identified after gelatin SDS-PAGE of lysates were also inhibited by serine protease inhibitors. Finally, incubation with chromogenic substrates indicated that midgut tissue and the protozoa lysates possessed proteases with subtilisin/chymotrypsin-like and trypsin-like activities while the lysates from fore- and hindgut tissues possessed proteases with almost exclusively trypsin-like activity. Our results suggest that C. formosanus not only produces endogenous proteases in their gut tissues but also possesses proteases originating from their protozoan symbionts. Further purification and characterization of individual proteases are ongoing.