Roy Gross, Department of Microbiology, Biocenter, University of Wuerzburg, Am Hubland, Wuerzburg, 97074, Germany and Heike Feldhaar, Department of Behavioural Physiology and Sociobiology, Biocenter, University of Wuerzburg, Am Hubland, 97074 Wuerzburg, Germany.
Blochmannia, the intracellular endosymbiont of carpenter ants and related genera resides in specialized bacteriocytes that are intercalated between midgut cells. Like in other intracellular endosymbionts the genome of Blochmannia is strongly reduced in size compared to its free-living relatives. In comparison to E. coli, Blochmannia has retained only about a sixth of the genes in its genome. Genes that are still present are supposedly important for the symbiotic interaction with the ant-host.
Among the genes of Blochmannia floridanus, that may be important for its host Camponotus floridanus, are those that encode all amino acids essential for the ant, a urease that may help in nitrogen-recycling, as well as genes for the metabolic pathway to reduce sulphate and synthesize cystein. However, as presence of genes within the endosymbiont´s genome does not necessarily mean that these metabolic pathways play a role for the host, we conducted feeding experiments with a holidic artificial diet to test the functions predicted by the genome sequence. These experiments confirm that Blochmannia provides the host with essential amino-acids. The capability of worker-groups of C. floridanus treated with antibiotics (to reduce the number of Blochmannia) were able to raise pupae from larvae at the same level as control groups when essential amino acids were provided in the artificial diet. In contrast, worker-groups treated with antibiotics that were not fed essential amino acids raised significantly fewer pupae. Additionally, feeding experiments using urea marked with stable isotopes (15N) show that the endosymbiont plays a role in nitrogen-recycling since the marked nitrogen was detected in the ant´s hemolymph in essential amino acids. We conclude that Blochmannia may enable the genera Camponotus and Polyrhachis to maintain large colonies in habitats that are strongly limited in nitrogen-resources, e.g. canopies of tropical rainforests where these two genera are species-rich and very abundant.
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