For confocal analysis five animals of each developmental stage were investigated. Confocal laser scanning microscopy (CLSM) Midguts were dissected from individuals and gut content washed out in sterile PBS. Subsequently the midgut samples were fixed on microscopic slides and permeabilized as described previously [13]. Hybridization was carried out by default with FITC-selleck labeled oligonucleotide Bfl172 specific for B. floridanus 16S rRNA which had been used successfully in a previous study for fluorescent in situ hybridization studies [13]. The probe was labeled with the dye

at the 5′end as described by the manufacturer (Metabion International AG, Planegg-Martinsried, Germany). Alternatively, red fluorescent Cy3-labeled Bfl172 was used. For CLSM with a Leica DMR laser scanning microscope (Leica Microsystems 3-Methyladenine price www.selleckchem.com/products/OSI-906.html GmbH, Wetzlar, Germany) these labeled oligonucleotides were applied in combination with SYTO Orange 83 (Molecular Probes Inc.) with a concentration of 2.5 – 5 μM in TE buffer, pH 7.4, resulting in unspecific nucleic acid counterstaining of cytoplasm as well as mitochondria and nuclei after 30 minutes post-FISH incubation and 5 minute washing in TE buffer

at room temperature. For actin-staining 0.5 ng/μl FITC-Phalloidin (Invitrogen Inc.) was used (the B. floridanus specific probe was coupled to Cy3 instead of FITC in the respective experiments). The dyes were used according to the manufacturers’ protocols. Confocal images were analyzed

with the Leica Application Suite Advanced Fluorescence Software (Leica Microsystems GmbH, Wetzlar, Germany). Each of the images shown is representative Thymidylate synthase for a series of preparations from the respective host stage with very similar appearances. For the quantification of Blochmannia population densities of ant guts in different larval developmental stages, exemplarily shown in Figure 1 to 10, were calculated as follows: optical sections of gut preparations were recorded by CLSM (see above). Images in the Leica-specific lif file format were opened as ImageJ hyperstacks [31] making use of the LOCI bio-formats plugin (http://​loci.​wisc.​edu/​software/​bio-formats). The stack corresponding to the FITC channel was thresholded and binarized. The area fraction of labeled Blochmannia symbionts was thus measured within each confocal slice. Area fractions were collected for each slice of a stack, summed up, and normalized for the number of slices. The resulting value was termed volume fraction of symbionts (Figure 12). Differences in volume fractions among developmental stages were compared using a one-factorial ANOVA, after homogeneity of variances had been confirmed by Levene’s test implemented in SPSS 15.0 (SPSS Inc. Chicago, Illinois, USA). Acknowledgements We thank Dagmar Beier and Achim Paululat for critical reading of the manuscript and Adrian Mehlitz for help with confocal microscopy.