Specialized Metabolites Reveal Evolutionary History and Geographic Dispersion of a Multilateral Symbiosis

Abstract

Fungus-growing ants engage in a multilateral symbiosis: they cultivate a fungal garden as their primary food source and host symbiotic actinobacteria ( Pseudonocardia spp.) that provide chemical defenses. The bacterial symbionts produce small specialized metabolites that protect the fungal garden from specific fungal pathogens ( Escovopsis spp.), and in return, they are fed by the ant hosts. Multiple studies on the molecules underlying this symbiotic system have led to the discovery of a large number of structurally diverse antifungal molecules, but somewhat surprisingly no shared structural theme emerged from these studies. A large systematic study of Brazilian nests led to the discovery of the widespread production of a potent but overlooked antifungal agent, which we named attinimicin, by nearly two-thirds of all Pseudonocardia strains from multiple sites in Brazil. Here we report the structure of attinimicin, its putative biosynthetic gene cluster, and the evolutionary relationship between attinimicin and two related peptides, oxachelin A and cahuitamycin A. All three nonribosomal peptides are structural isomers with different primary peptide sequences. Attinimicin shows iron-dependent antifungal activity against specific environmental fungal parasites but no activity against the fungal cultivar. Attinimicin showed potent in vivo activity in a mouse Candida albicans infection model comparable to clinically used azole-containing antifungals. In situ detection of attinimicin in both ant nests and on worker ants supports an ecological role for attinimicin in protecting the fungal cultivar from pathogens. The geographic spread of the attinimicin biosynthetic gene cluster in Brazilian Pseudonocardia spp. marks attinimicin as the first specialized metabolite from ant-associated bacteria with broad geographic distribution.

Cave Microbes as a Potential Source of Drugs Development in the Modern Era

“…Bacteria are symbiotic with cave animals (beetles, salamanders, isopods, cave crickets, millipedes and insects, and other arthropods). Bacteria protect cave animals from fungal attacks by killing pathogenic fungi through secretion of bioactive antifungal metabolites [ 81 ]. Insects and arthropods produce various antifungal compounds, such as specialist peptides, cuticular excretions, venoms, and hemolymph.…”

Ammonia Production by Streptomyces Symbionts of Acromyrmex Leaf-Cutting Ants Strongly Inhibits the Fungal Pathogen Escovopsis

“…With the identification of the antifungal compounds from leaf-cutting ant symbionts, we started to gain an in-depth picture on the chemistry of the interspecies interactions in the microcosmos of leaf-cutting ants. In the last decade, a growing variety of polyketide and non-ribosomal peptide antifungals, e.g., candicidin [ 22 ], dentigerumycin [ 23 , 26 ], nystatin P1 [ 25 ], antimycins [ 27 , 28 ] or attinimycins [ 29 ], have been characterized from microbial symbionts of different leaf-cutting ant species indicating the diversity of defense mechanisms. Some of the antifungals appear to be common and widespread among symbionts of leaf-cutting ants and even occur at different geographical locations [ 22 , 25 , 29 ].…”

“…In the last decade, a growing variety of polyketide and non-ribosomal peptide antifungals, e.g., candicidin [ 22 ], dentigerumycin [ 23 , 26 ], nystatin P1 [ 25 ], antimycins [ 27 , 28 ] or attinimycins [ 29 ], have been characterized from microbial symbionts of different leaf-cutting ant species indicating the diversity of defense mechanisms. Some of the antifungals appear to be common and widespread among symbionts of leaf-cutting ants and even occur at different geographical locations [ 22 , 25 , 29 ]. Some secondary metabolites from microbial symbionts of leaf-cutting ants were directly identified in their biological context (e.g., on the ants’ integument or in waste material) thus strongly suggesting their ecological function [ 27 , 29 ].…”

“…Some of the antifungals appear to be common and widespread among symbionts of leaf-cutting ants and even occur at different geographical locations [ 22 , 25 , 29 ]. Some secondary metabolites from microbial symbionts of leaf-cutting ants were directly identified in their biological context (e.g., on the ants’ integument or in waste material) thus strongly suggesting their ecological function [ 27 , 29 ]. So far, all antimicrobial compounds from microbial symbionts were—as expected—complex secondary metabolites of polyketide or non-ribosomal peptide origin.…”

Aspectos químicos e filogenéticos envolvidos na simbiose entre >i<Amycolatopsis>/i< e formigas attina

“…Recentemente, um estudo sistemático com ninhos de formigas levou ao isolamento do composto attinimicina (2) (Figura 2), um novo peptídeo não ribossomal com atividade antifúngica e também seletivo frente ao Escovopsis. Tal composto foi detectado em 70% das linhagens de Pseudonocardia coletadas no Brasil, o que indica que ele possui um papel ecológico importante para os organismos envolvidos na simbiose (FUKUDA et al, 2021).…”