Bacterial communities associated with the hindgut of Tipula abdominalis larvae (Diptera: Tipulidae), a natural biorefinery
Cook, Dana Marie
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Insects are the largest taxonomic group of animals on earth. Although a few thorough studies have shown insect guts host high microbial diversity, many insect-microbe associations have not been investigated. Tipula abdominalis is an aquatic crane fly ubiquitous in riparian environments. T. abdominalis larvae are shredders, a functional feeding group of insects that consume coarse particulate organic matter, primarily leaf litter. In small stream ecosystems, leaf litter comprises the majority of carbon and energy inputs; however, many organisms are unable to degrade this lignocellulosic material. By converting lignocellulose into a form that other organisms can use, T. abdominalis larvae influence the bioavailability of carbon and energy within the ecosystem. Evidence suggests that the bacterial community associated with the T. abdominalis larval hindgut facilitates the digestion of its recalcitrant lignocellulosic diet. Such lignocellulose-ecosystem-insect-microbiota interactions provide a model natural biorefinery and have become of special interest recently for the application of microbial conversion of lignocellulose to biofuels, including ethanol, butanol, and hydrogen. Bacterial isolates from the T. abdominalis larval hindgut were characterized, and many had enzymatic activity against plant polymer model substrates. Several isolates had low 16S rRNA gene sequence similarity to previous described bacteria, including the proposed novel genus Klugiella xanthotipulae gen. nov., sp. nov. Clone libraries of the 16S rRNA gene revealed a phylogenetically diverse bacterial community associated with the larval hindgut wall epithelial and lumen material. Clostridia and Bacteroidetes dominated both hindgut wall and lumen, while Betaproteobacteria dominated leaf diet- and cast-associated microbiota. Although phylogenetic structure at the class level was similar between hindgut wall and lumen microbiota and between leaf diet and cast microbiota, statistical analyses suggest that these sub-communities are significantly different from one another. Enrichment cultures were constructed to cultivate a dynamic cellulolytic subpopulation from the hindgut microbiota. Although the phylogenetic structure of the cellulolytic enrichment cultures was highly variable, function remained stable over successive transfers of subcultures. The T. abdominalis larval hindgut hosts a novel phylogenetically diverse and dynamic microbial community.