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Diversity, molecular monitoring and genomics of Blattabacterium spp., the obligatory bacterial endosymbionts of cockroaches

Final Activity Report Summary - ENDOBLATTA (Diversity, molecular monitoring and genomics of blattabacterium spp., the obligatory bacterial endosymbionts of cockroaches)

In the course of this project, the bacterial endosymbionts of cockroaches, called blattabacteria, were studied, focussing on the analysis of their genomes. Three different cockroaches, blattella germanica, periplaneta americana and blatta orientalis were studied and compared. An initial phylogenetic analysis showed the consistency with the formerly established models of co-evolution between host and symbiont.

As a primary step Fluorescence in situ hybridisation (FISH) was used to prove that the blattabacteria were the only endosymbionts in the fat body of the cockroaches. The absence of any other bacteria and therefore the unique presence of blattabacteria were confirmed for all three cockroaches.

Furthermore, as a first step of the genome analysis, the sizes of the genomes of the three endosymbionts were determined via Pulsed field gel electrophoresis (PFGE). All three symbionts of the three cockroach species had genome sizes of about 650 kb. This clearly indicated genome reduction, like it was common for bacterial endosymbionts of insects.

As another feature the degree of ploidy, i.e. the copy number of the chromosomes, per bacterial cell was determined using a quantitative real time polymerase chain reaction (RT-PCR) approach. In this way genome copy numbers of between 10 and 18 for p. americana and 320 and 353 for bl. orientalis were measured. These results showed that blattabacteria contained multiplied genomes in their cells and might in this way contribute to an enhanced expression of genes crucial for the symbiosis, similar to relevant findings for buchnera aphidicola in aphids.

A central part of the project consisted of the sequencing of the complete genome of a blattabacterium. For this purpose the endosymbiont of b. germanica was selected. However, due to unforeseen problems with contaminating Deoxyribonucleic acid (DNA) stemming from the host, which severely hindered the efficient generation of shot-gun libraries and the specific sequencing of the DNA from the blattabacterium, the sequencing project could not be finished by the time of the project completion. Up to this point 330 kb, equalling to 52 % of the genome, were assembled in 320 contigs. A preliminary analysis showed a clear affiliation within the phylum bacteroidetes with, however, quite distinct features that confirmed its placement as own lineage within this group.