Bacteria Associated with the Gut Tract of Larval Stages of the Aquatic Cranefly Tipula abdominalis (Diptera; Tipulidae).

Scanning electron microscopy, light microscopy, and direct isolations were used to examine the distribution and diversity of bacteria in the gut tracts of larval stages of Tipula abdominalis. The animal had an enlarged hindgut which housed a diverse bacterial community in the lumen and directly attached to the gut wall. Distinct localization was noted, with the most dense and most diverse community anterior to the rectum. A distinct architecture of bacteria occurred in this region, characterized by a layering or a "weblike" array of filamentous bacteria overlying mats of bacteria closely associated with the gut wall. Although morphological diversity was high in the hindgut, filamentous bacteria were the dominant morphology observed. The attached microbiota, sloughed during ecdysis, recolonized to the same density and diversity observed before the molt. The majority of the isolatable bacterial types were facultatively anaerobic. The distinct localization and attached nature of the hindgut bacteria and the recolonization after each molt suggest they are indigenous to this region of the gut tract.