Diversidade e evolução na simbiose entre bactérias e formigas Attini

• Autor(a) principal: Marchiori, Ana Carolina [UNESP]
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/110397
• topic: Ants; Formiga; Simbiose; Microbiota; Formigas - Nutrição; Bacterias; Formiga-cortadeira; Nitrogenio - Fixação

Ants of the Attini tribe are known for the habit of cultivating mutualistic fungi (Basidiomycota) on a variety of harvested materials to form what is called the fungus garden. This habit originated approximately 50 million years ago in South America and gave rise to five agricultural systems, which differ in the type of fungus and collected material. Attine ants utilize the fungus garden as a source of nutrients and enzymes, which are not only produced by the mutualistic fungus, but also by other microbes present in the garden. Therefore, for ants and fungi have access to these nutrients associations with other microorganisms became necessary. Studies of microbial community associated with attine ants are mostly related to the fungus gardens and aim to explore the mechanisms of plant biomass degradation. Information on the microbiota associated with the body of ants and its function are still lacking. Attine ants rely on microbial symbionts for nutrition and protection against parasites. On the other hand, some microbes threatens these ants and others appear to be only commensals. In this work, the bacteria associated with the attine ants Atta laevigata, Trachymyrmex urichi and Mycocepurus goeldii were identified by culture-independent methods and a scenario in which the evolution of attine ants is shaped by the interaction with these microorganisms has been proposed. In the present study a washing protocol was also developed to remove external bacteria, and used to sample microorganisms living inside the ants and possibly other insects. The results showed differences between the bacterial communities harbored by the attine ants studied. Discrimination of internal and external ants’ body bacteria was possible due to the standardization and application of the developed washing protocol. It was observed that the intestines of most basal attine M. goeldii are dominated by a single species of Spiroplasma. However, during the attine ants’ evolution, this bacterium was progressively replaced by two Rhizobiales species in the gut of the phylogenetically intermediate T. urichi, and finally a single species of Rhizobiales prevailed as the unique bacterial species in the gut of the most derived leaf-cutter ant A. laevigata. Leaf-cutters also harbor on their cuticles considerable amounts of Acetobacter sp. Both Rhizobiales and Acetobactersp. species are in the group of nitrogen-fixing bacteria. Thus, it is conceivable that specialization in nitrogen-fixing mutualists may have played a role in increasing population and body size during Attini evolution. A larger population is thought to be associated with increases in infection rates, but this tendency was apparently counterbalanced by high social complexity of leaf-cutters and by the maintenance of Burkholderiales and Actinomycetales species, which we only found in the cuticle of ants. These antibiotic-producing bacteria may have assumed the protective role that is currently attributed to Pseudonocardiaceae in the remaining Attini species. We also detected an association with cuticular Wolbachia mutualists, which may have begun in the more primitive Attini, then specialized in the intermediate ones, and finally being lost in the more derived leaf-cutters. Mutualistic associations appear to be recent and originated from a single acquisition of nitrogen-fixing bacteria and multiple acquisitions of antibiotic producing microbes.