Distribution of the obligate endosymbiont Blochmannia floridanus and expression analysis of putative immune genes in ovaries of the carpenter ant Camponotus floridanus

Abstract

The bacterial endosymbiont Blochmannia floridanus of the carpenter ant Camponotus floridanus contributes to its hosts' ontogeny via nutritional upgrading during metamorphosis. This primary endosymbiosis is essential for both partners and vertical transmission of the endosymbionts is guaranteed by bacterial infestation of oocytes. Here we present a detailed analysis of the presence and localisation of B. floridanus in the ants' ovaries obtained by FISH and TEM analyses. The most apical part of the germarium harbouring germ-line stem cells (GSCs) is not infected by the bacteria. The bacteria are detectable for the first time in lower parts of the germarium when cystocytes undergo the 4th and 5th division and B. floridanus infects somatic cells lying under the basal lamina surrounding the ovarioles. With the beginning of cystocyte differentiation, the endosymbionts are exclusively transported from follicle cells into the growing oocytes. This infestation of the oocytes by bacteria very likely involves exocytosis-endocytosis processes between follicle cells and the oocytes. Nurse cells were never found to harbour the endosymbionts. Furthermore we present first gene expression data in C. floridanus ovaries. These data indicate a modulation of immune gene expression which may facilitate tolerance towards the endosymbionts and thus may contribute to their transovarial transmission.

Alternative Transmission Patterns in Independently Acquired Nutritional Cosymbionts of Dictyopharidae Planthoppers

“…In some heteropteran bugs but also carpenter ants, symbiotic gammaproteobacteria infect early previtellogenic oocytes directly: infect follicular cells, gather in their cytoplasms, and then enter the oocyte’s cytoplasm via an endocytic pathway. In both cases, initially, symbionts are dispersed in the entire ooplasm, but during vitellogenesis they accumulate and form a “symbiont ball” ( 54 , 55 ). In some host lineages, enterobacterial symbionts have adopted more exotic transmission strategies.…”

Camponotus floridanus Ants Incur a Trade-Off between Phenotypic Development and Pathogen Susceptibility from Their Mutualistic Endosymbiont Blochmannia

“…The endosymbiont upgrades the host diet through recycling nitrogen and aiding in the synthesis of amino acids, fatty acids, and nucleotides [ 23 , 24 , 25 , 26 ], which are key in their pupal stage given the symbiont’s proliferation [ 27 , 28 ], gene expression [ 29 , 30 ], and the high fecundity of colonies compared to those with experimentally-reduced Blochmannia [ 25 , 29 , 31 ]. The ants tolerate the symbiont within bacteriocytes and ovaries; for example, Camponotus floridanus ants alter their expression of immunomodulators to reduce their immune response within these tissues [ 32 , 33 ]. The rest of the body maintains normal immune gene expression [ 32 ] unless Blochmannia floridanus is found in the haemocoel, at which point an immune response is mounted [ 34 ] that indicates the hosts’ readiness to prevent the spread of symbionts.…”

Gene Expression Profile Analysis is Directly Affected by the Selected Reference Gene: The Case of Leaf-Cutting Atta Sexdens

“…We have observed in some studies about gene expression in ants the use of only a single reference gene without any mention of its validation. Expression analyzes of genes involved in immunological responses, such as PGRP-LB and PGRP-SC2 in the ant Camponotus floridanus were normalized with only one reference gene, the RPL32 [ 32 ]. Similarly, the reference gene β-actin was the only one used for normalization of Calreticulin gene expression [ 33 ] and Muscarinic Cholinergic receptor [ 34 ] in studies with Polyrhachis vicina.…”