In situ morphology of the gut microbiota of wood-eating termites [Reticulitermes flavipes (Kollar) and Coptotermes formosanus Shiraki]

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Abstract
Light microscopy and scanning and transmission electron microscopy were used to examine the in situ morphology of the gut microbiota of Reticulitermes flavipes and Caoptotermes formosanus. Laboratory-maintained termites were used and, for R. flavipes, specimens were also prepared immediately after collection from a natural infestation. The latter endeavor enabled a study of different castes and developmental stages of R. flavipes and revealed differences in the microbiota of field versus laboratory specimens. The termite paunch microbiota consisted of an abundance of morphologically diverse bacteria and protozoa. Thirteen bacterial morphotypes in the paunch were described in detail: seven were observed only in R. flavipes, three were observed only in C. formosanus, and three were common to both termite species. The paunch epithelium was densely colonized by bacteria, many of which possessed holdfast elements that secured them tightly to this tissue and to other bacterial cells. Besides bacteria, the protozoan Pyrsonympha vertens adhered to the paunch epithelium of R. flavipes by means of an attachment organelle. Cuplike indentations were present on the paunch epithelial surface and were sites of bacterial aggregation. Ultrastructural features of cups suggested their involvement in ion absorption. In addition to the paunch, the midgut was also colonized by bacteria that were situated between epithelial microvilli. Results suggest that bacteria are an integral part of the gut ecosystem.