Two +ssRNA mycoviruses cohabiting the fungal cultivar of leafcutter ants

Abstract

Leafcutter ants are dominant herbivores in the Neotropics and rely on a fungus (Leucoagaricus gongylophorus) to transform freshly gathered leaves into a source of nourishment rather than consuming the vegetation directly. Here we report two virus-like particles that were isolated from L. gongylophorus and observed using transmission electron microscopy. RNA sequencing identified two +ssRNA mycovirus strains, Leucoagaricus gongylophorus tymo-like virus 1 (LgTlV1) and Leucoagaricus gongylophorus magoulivirus 1 (LgMV1). Genome annotation of LgTlV1 (7401 nt) showed conserved domains for methyltransferase, endopeptidase, viral RNA helicase, and RNA-dependent RNA polymerase (RdRp). The smaller genome of LgMV1 (2636 nt) contains one open reading frame encoding an RdRp. While we hypothesize these mycoviruses function as symbionts in leafcutter farming systems, further study will be needed to test whether they are mutualists, commensals, or parasites.

Keywords: Botourmiaviridae; Fungus-farming ant; Leafcutter ant; Leucoagaricus gongylophorus; Magoulivirus; Ourmia-like virus; Symbiosis; Tymo-like virus; Tymovirales; Tymovirus.

Fig. 1

TEM images of negative stained virus-like particles (VLPs) extracted from L. gongylophorus fungal isolates farmed by A. colombica (Ac2012-1) and the fecal fluid of the worker ants from the same colony. VLP1 presents a 30-nm wide icosahedral geometry with a high similarity to known tymovirus virions [25]. VLP2 has a 15-nm wide bacilliform morphology and varies between 30 and 100 nm long like known virions of ourmiaviruses in the family Botourmiaviridae [26, 27]. The scale bar for all panels is 50 nm

Fig. 2

Phylogenetic placement and genomic structure of Leucoagaricus gongylophorus tymo-like virus 1 (LgTlV1) A maximum-likelihood phylogenetic tree based on RdRp alignment (1755 aa) showing the position of LgTlV1 (green) within the order Tymovirales. Support values on the branches are ultrafast bootstrap values calculated with 1000 replicates (only shown UFBoot ≥ 50). The scale bar indicates 0.5 amino acid substitutions per site. B Genome structure with ORF positions and conserved sequence regions predicted

Fig. 3

Phylogenetic placement and genomic structure of Leucoagaricus gongylophorus magoulivirus 1 (LgMV1). A Maximum-likelihood phylogenetic tree based on RdRp alignment (1748 aa) showing the position of LgMV1 (green) within the family Botourmiaviridae. Support values on the branches are ultrafast bootstraps calculated with 1000 replicates (only shown UFBoot ≥ 50). The scale bar indicates 0.5 amino acid substitutions per site. B LgMV1 contains a single ORF that is highly similar to known RdRp sequences