Tissue Localization of the Endosymbiotic Bacterium “ Candidatus Blochmannia floridanus” in Adults and Larvae of the Carpenter Ant Camponotus floridanus

Abstract

The distribution of endosymbiotic bacteria in different tissues of queens, males, and workers of the carpenter ant Camponotus floridanus was investigated by light and electron microscopy and by in situ hybridization. A large number of bacteria could be detected in bacteriocytes within the midguts of workers, young virgin queens, and males. Large amounts of bacteria were also found in the oocytes of workers and queens. In contrast, bacteria were not present in oocyte-associated cells or in the spermathecae of mature queens, although occasionally a small number of bacteria could be detected in the testis follicles of males. Interestingly, the number of bacteriocytes in mature queens was strongly reduced and the bacteriocytes contained only very few or no bacteria at all, although the endosymbionts were present in huge amounts in the ovaries of the same animals. During embryogenesis of the deposited egg, the bacteria were concentrated in a ring of endodermal tissue destined to become the midgut in later developmental stages. However, during larval development, bacteria could also be detected in other tissues although to a lesser extent. Only in the last-instar larvae were bacteria found exclusively in the midgut tissue within typical bacteriocytes. Tetracycline and rifampin efficiently cleansed C. floridanus workers of their symbionts and the bacteriocytes of these animals still remained empty several months after treatment had ceased. Despite the lack of their endosymbionts, these adult animals were able to survive without any obvious negative effect under normal cultivation conditions.

Relevance of the Endosymbiosis of Blochmannia floridanus and Carpenter Ants at Different Stages of the Life Cycle of the Host

“…To investigate a possible role of Blochmannia at the colony level, experiments were carried out with animals treated with rifampin, which, as previously described, causes a strong decrease of the bacterial load in treated animals (19). Confirming the previous results, rifampin treatment did not interfere significantly with the viability of the adult workers and no obvious toxic effect on these animals could be noted.…”

“…Subsequently, the mother colony (including the queen and thus all brood produced by the queen) and one of the worker groups were treated with the antibiotic rifampin (C 43 H 58 N 4 O 12 ; Serva Elektrophorese GmbH); the other worker group, used as a control, was not. The antibiotic was fed to the ants twice a week over a period of 13 weeks in a solution containing 1% rifampin, 49.5% water, and 49.5% honey (wt/wt) as described previously (19). Workers that died were not replaced with workers from the mother colony, and thus the numbers of workers in the subcolonies decreased steadily during the experimental period.…”

“…The bacterial endosymbionts reside in specialized cells, the bacteriocytes, which are intercalated between enterocytes of the midgut tissue of the host. In females, the bacteria also occur in the oocytes, leading to a vertical transmission of the bacteria (6,13,19,20). Blochmannia is closely related to other insect endosymbionts, like Wigglesworthia glossinidia, the endosymbiont of the tsetse fly Glossina brevipalpis, and Buchnera aphidicola, the endosymbiont of aphids (1,2,3,9,11,22).…”

‘Candidatus Streptomyces philanthi’, an endosymbiotic streptomycete in the antennae of Philanthus digger wasps

“…For hybridization within the antennae, fresh antennae from female beewolves were cut into sections with a razor blade and glued onto microscope slides. Fixation and pre-treatment of the samples was performed following a previously described protocol (Sauer et al, 2002). Hybridization was carried out as for the bacterial samples, but with 3 h incubation with the labelled probe.…”

Metabolic Interdependence of Obligate Intracellular Bacteria and Their Insect Hosts

“…generally feed on a complex diet composed of dead and alive insects, bird excrement, and sweet food wastes. Despite their complex diet, these animals are endowed with bacterio-cytes carrying obligate intracellular bacteria of the genus "Candidatus Blochmannia" (10,104,105,109). On the other hand, a recent survey of ants living in tropical rain forest canopies has shown that at least in this geographical region, ants, including many Camponotus species, can be considered to be "secondary herbivores" since they may feed mainly on plant or insect exudates and are not predators or scavengers (24).…”