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Abstract:
This thesis comprises an array of studies about the bacterial gut microbiota in cockroaches and termites belonging to the superorder Dictyoptera. A high-throughput sequencing method, namely 454 pyrotag sequencing, was established and tested to analyzing bacterial 16S rRNA genes in intestinal tracts of insects. For this purpose the microbial communities within the gut compartments of the higher wood-feeding termite Nasutitermes corniger were investigated. In addition, physicochemical gut conditions of this termite were measured. Furthermore, a broad survey of specimen covering all families and subfamilies of cockroaches and lower and higher termites, including all known feeding habits, was conducted to investigate evolutionary and dietary patterns of their gut microbiota. The comprehensive study linking physicochemical gut conditions with the structure of the microbial communities in the different gut compartments of N. corniger revealed the dilated hindgut paunch (P3) as the densest colonized gut compartment dominating the whole microbial gut community. This compartment accumulates high hydrogen partial pressures (up to 12 kPa), which was apparently produced by the dense community of Spirochaetes and Fibrobacteres dominating also the gut of other Nasutitermes species. All other compartments such as the alkaline P1 (average pH 10.0) comprised small but distinct populations characteristic for each gut region. Finally, similarities in the microbial communities of posterior hindgut and crop suggested that proctodeal trophallaxis or coprophagy is present also in higher termites. The study of the Dictyoptera hindgut microbiota could show that the cockroach microbial gut community is more diverse and less specialized than that of the termites. Both differ significantly in their composition already on phylum level. The emerging patterns document a long history of (co)evolution of the gut microbiota with their dictyopteran host species. This resulted in clear and distinct clustering of the hosts concerning their phylogenetic relationship and dietary demands. Many of the bacterial lineages causing this clustering (e.g., Fibrobacteres, Treponema, and Bacteroidetes Cluster V) seem to be ubiquitous, albeit very rare in most of the Dictyoptera. The gut could serve as a reservoir of diverse bacteria that seem to exploit specific niches only in exclusive phylogenetic or dietary groups of host guts. Furthermore, the analyses could add to the inherent peculiar position of the wood-feeding cockroach Cryptocercus punctulatus sharing many microbial core taxa with the cockroaches, lower, and the higher termites. Statistical analyses verified the phylogenetic position of Cryptocercus hindgut microbiota in between the termites and cockroaches.
