Alteration of the gut microbiota and its effect on nitrogen metabolism in termites

Abstract

When the spirochaetes in the gut of Nasutitermes exitiosus were killed with oxygen, the glutamate dehydrogenase activity of whole termite extracts declined by some 75%. Starvation, which caused a similar termite mortality rate to oxygen treatment, did not greatly affect this enzyme. Treatment of N. exitiosus with tetracycline to kill all the gut flora led to glutamate dehydrogenase activity falling to zero. Treatment of Coptotermes lacteus with oxygen to kill gut protozoa and spirochaetes resulted in the activity of glutamate dehydrogenase remaining low, whereas in starved and normal termites the activity of the enzyme increased about seven-fold. A similar result was observed when tetracycline was used to kill the gut flora and fauna. Aspartate aminotransferase and alanine aminotransferase activities (which appear to be of termite origin) were little affected by these treatments. The glutamate dehydrogenase was NAD +-dependent and was not found in the bacteria (excluding spirochaetes) colonising the hindgut. In all experiments there was a slight increase in the uric acid content of the termites in both control and treated insects. The free amino acid content of both species of termites was increased (about 50%) when they were starved, but was little affected when the gut flora and/or fauna were killed. Thus the gut flora and fauna do not appear to be involved in amino acid metabolism. When C. lacteus was kept under argon-oxygen mixtures for seven weeks the total nitrogen, enzyme activities and uric acid content were similar to those of termites kept under nitrogen-oxygen mixtures. These results indicate that in the short term termites do not need to fix nitrogen and also that nitrogen is well conserved.