Natural products from microorganisms associated with nests of the leaf-cutter ant Atta sexdens rubropilosa

Author(s)

Eduardo Afonso da Silva Junior

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Ciências Farmacêuticas de Ribeirão Preto (PCARP/BC)
• Defense date: 2017-03-24

Examining board members

Monica Tallarico Pupo; Mauricio Bacci Junior; Fernando Batista da Costa; Antonio Eduardo Miller Crotti; Paulo Henrique Gorgatti Zarbin

• Advisor: Monica Tallarico Pupo; Jon Clardy

Abstract

Leaf-cutter ants collect plant material to cultivate their food source, a symbiotic fungus. Their colonies can be attacked by invading microorganisms and the ants have associated with protective antibiotic-producing bacteria. This work aimed to study the natural products produced by microorganisms associated with nests of the leaf-cutter ant Atta sexdens rubropilosa. Ants and fungal garden samples were washed with sterile aqueous solution and bacteria of the genera Serratia, Pseudonocardia and Burkholderia were isolated using ISP-2 and chitin agar plates. Serratia marcescens 3B2 produces 3-ethyl-2,5-dimethyl-pyrazine and 2,5-dimethyl-pyrazine, which are components of the ant trail pheromone, and the components of the metapleural glands secretions indole-3-acetic acid and phenylacetic acid were also produced by this strain. Serratia marcescens 3B2 genome was sequenced and the production of the antibiotics andrimid, oocydin A and serratamolide were identified by genome mining and dereplication of the crude extracts. Isotope labeling experiments have revealed that the amino acid L-threonine is the biossyntetic precursor of 2,5-dimethylpyrazine and 3-ethyl-2,5-dimethylpyrazine. Pseudonocardia spp., isolated from the ants and fungal garden, inhibited the growth of the fungus Escovopsis sp., a specialized fungal garden parasite. A bioassay-guided isolation of the Pseudonocardia sp. 1B7 ethyl acetate extract revealed indole-3-acetic acid as the active compound. This natural product selectively inhibited the spores growth of five Escovopsis spp. strains and it was not active against the fungal cultivar Leucoagaricus gongylophorus. Isotope feeding experiments and whole-genome sequencing of Pseudonocardia sp. 1B7 indicated that indole-3-acetic acid is biosynthesized by L-tryptophan dependent pathway. Burkholderia sp. JB2 was isolated from the fungal garden and it produces the antibiotic tropolone, which inhibits the Escovopsis sp. growth by iron privation. The fungal gardens produce a water-resistant layer that seems to be related to the garden protection, as evidenced by scanning electron microscopy analysis. The entomopathogenic fungus Aspergillus nomius ASR3 was isolated from a dead Atta sexdens rubropilosa queen and the aflatoxins B1 and G1 were produced by this fungus in laboratory and natural conditions. The results highlight the importance of bacterial microbiota for the defense and communication of Atta sexdens rubropilosa. These results could contribute for future development of new therapeutic strategies and environmentally friendly techniques to control leaf-cutter ants (AU)

• FAPESP's process: 12/24204-1 - Natural products involved in chemical and biological interactions of microorganisms associated to nests of the leaf-cutting ants Atta sexdens rubropilosa
• Grantee: Eduardo Afonso da Silva Junior
• Support Opportunities: Scholarships in Brazil - Doctorate