In Vitro Studies Reveal that Pseudomonas, from Odontotermes obesus Colonies, can Function as a Defensive Mutualist as it Prevents the Weedy Fungus While Keeping the Crop Fungus Unaffected.

Abstract

Insects that farm monocultures of fungi are canonical examples of nutritional symbiosis as well as independent evolution of agriculture in non-human animals. But just like in human agriculture, these fungal crops face constant threat of invasion by weeds which, if unchecked, take over the crop fungus. In fungus-growing termites, the crop fungus (Termitomyces) faces such challenges from the weedy fungusPseudoxylaria.The mechanism by whichPseudoxylariais suppressed is not known. However, evidence suggests that some bacterial secondary symbionts can serve as defensive mutualists by preventing the growth ofPseudoxylaria.However, such secondary symbionts must possess the dual, yet contrasting, capabilities of suppressing the weedy fungus while keeping the growth of the crop fungus unaffected. This study describes the isolation, identification, and culture-dependent estimation of the roles of several such putative defensive mutualists from the colonies of the wide-spread fungus-growing termitefrom India,Odontotermesobesus. From the 38 bacterial cultures tested, a strain of Pseudomonas showed significantly greater suppression of the weedy fungus than the crop fungus. Moreover, a 16SrRNApan-microbiome survey, using the Nanopore platform, revealedPseudomonasto be a part of the core microbiota ofO. obesus. A meta-analysis of microbiota composition across different species of Odontotermesalso confirms the widespread prevalence ofPseudomonaswithin this termite. These lines of evidence indicate that Pseudomonascould be playing the role of defensive mutualist withinOdontotermes.