Transcriptional profiling of the endosymbiont Blochmannia floridanus during different developmental stages of its holometabolous ant host

Abstract

The transcriptome of Blochmannia floridanus, the endosymbiont of the carpenter ant Camponotus floridanus, is presented during various developmental stages of its holometabolous host by use of a whole-genome DNA macroarray. The detected transcription patterns indicate the presence of local transcription units as well as global regulatory mechanisms. Yet, the overall regulation scale is very modest, rarely exceeding a factor of three. A large number of genes show differential expression in different life stages and a distinct expression pattern of genes possibly involved in symbiotic function as compared with housekeeping genes is apparent. However, these transcriptional changes are small as compared with the changes in the number of bacteria during host development, which is the highest in pupae and in young imagines. Control of replication of the bacteria in certain life stages may therefore be the decisive parameter influencing the overall level of gene expression of Blochmannia in the animal. The few highly expressed genes like those encoding molecular chaperones exhibit a significantly higher G+C content than moderately expressed genes.

Promoter Characterization in the AT-Rich Genome of the Obligate Endosymbiont “ Candidatus Blochmannia floridanus”

“…Blochmannia." In a recent survey of transcription profiles of the endosymbiont during different developmental stages of the holometabolous host animals, only minor transcriptional changes were noted (15). This is in line with the fact that most of the transcription regulators present in free-living relatives within the Enterobacteriaceae have been lost in "Ca.…”

“…It is interesting that most of these genes belong to the most strongly expressed factors in "Ca. Blochmannia floridanus" (15). Again, well-defined transcriptional start sites were found in front of each gene which in all cases corresponded to the predicted promoters ( Fig.…”

“…Blochmannia floridanus" as well as in Buchnera aphidicola, the closely related obligate endosymbiont of aphids, overall gene organization resembles that of the free-living relative E. coli (5,14). Here, numerous intergenic sequences of considerable length are present, and in many cases genes can be assigned to specific operons or consist of single transcription units (15). However, since RpoD-dependent promoters are AT rich, their reliable bioinformatic prediction is very difficult in these strongly AT-biased genomes.…”

“…4A). To further corroborate and refine these data, we isolated the bacteria from the animals as described previously (15). Then we subjected them to a heat shock at 42°C, whereas controls were kept at 25°C, and followed expression of the groEL, groES, dnaK, dnaJ, grpE, and lon genes during a time course of up to 30 min using E. coli DH5␣ as a control.…”

“…These factors were selected either because of the presence of relatively long nontranslated intergenic regions in front of the genes or because they are transcribed in the opposite direction from the upstream gene, suggesting the presence of specific promoters. Bacteria were isolated from their host animals as described recently by Stoll et al (15), and primer extensions with bacterial whole-cell RNA were performed as described previously using the primers shown in Table 1 (6). In most cases one or a few defined transcription start points are found, usually with one transcript being most abundant (Fig.…”