We have confirmed that termite fungus combs are vastly dominated by Termitomyces, and showed that this is not driven by obligate gut passage of substrates. This points to key behavioural and chemical defences of termite or the food fungus, Termitomyces. This is in line with our discovery that termites avoid substrates with virulent pathogens, and that termites rapidly use soil to cover exposed fungal gardens (WPIII). Cultivation efforts have allowed us to establish a series of putative pathogens to be used to test defences (WPIII) and for future experimental evolution work (WPII). Gut metabolome analyses from South African species is progressing, including network analyses and caste-specific compound identification, forming the backbone for new comparative metabolome analyses and for linking metabolome differences to differences in microbial communities (WPI). Our hypothesis that Termitomyces plays a major role in defence appears to hold true and work is now in progress to understand the role of volatiles of fungal origin in defence (WPI, III). This is supported by the sequencing of a number of Termitomyces species, for which analyses of biosynthetic gene clusters is progressing. Volatiles should only be able to play a prophylactic role in the symbiosis if the environment within which Termitomyces is maintained remains sealed from the surroundings. This is consistent with the hypothesis that layers of defence are essential to keep fungal gardens free from pathogens, and this does indeed appear to be prioritised by the termite host as indicated above. Gut metagenomics has proven challenging for biosynthetic gene cluster (BGC) characterisation, because of fragmented metagenomes and challenges associated with linking gene clusters to metabolites present in these complex environments. With novel approaches to metabarcoding BGC domains will be employed during 2021 to help overcome these challenges and identify the diversity and types of gene clusters prevalent in termite guts and fungal gardens. We have however through comparative genomics analyses established that Actinobacteria – well known for their unprecedented capacity to code for and secrete compounds with antimicrobial properties – are consistently present and rich in biosynthetic gene clusters. This supports that the prospects for novel compound discovery remains high, despite past efforts to identify chemical compounds of actinobacterial origins in the symbiosis.
A major goal of this action has been to improve protocols for establishing fungus-growing termites in the laboratory in the Ivory Coast where we perform field work and subsequently at the University of Copenhagen (WPIII). As expected, this has proven challenging, with our initial efforts nevertheless providing promising insights into the conditions that favour successful setups. Specifically, we attempted to establish >400 queen and king pairs of Ancistrotermes cavithorax in the laboratory in Copenhagen, but establishment of fungal gardens proved to be a critical point during the colony life cycle, with consequently very low success rates. We continue to work with local field assistants and partners in Ivory coast and now have a few colonies in the lab in Copenhagen and efforts are ongoing in Lamto. Major recent achievements include a comprehensive review published in Natural Product Reports (Schmidt et al. 2022), which is associated with a manually curated online database (
WPI, publication of termite gut metabolomes (Vidkjær et al. 2022) and microbial impacts on termite biology (Murphy et al. 2022) (WPI,III). We have finalised comparative genomics analyses of 39 Termitomyces genomes (20 species) and established their evolutionary histories (Schmidt et al. in preparation). These analyses – along with volatile analyses (Kreuzenbeck et al., 2022) – support that Termitomyces plays a major role in defence (WPI,II). The use of volatile terpenes in defence is possible because the termites ensure an enclosed, homeostatic environment that ensure constant temperature and humidity. This allows for CO2 build-up well beyond what most organisms can tolerate (5% or higher), and we have therefore also tested whether extremely high CO2 help protect from fungal infections, which appears to be the case; thus indicating that the environment acts as an additional layer of defence of the farming symbiosis (WPIII).