Symbioses: An environmentally-relevant source of natural substances in the search for antimicrobial compounds

Novel antifungal and antibacterial principles with greater efficacy are urgently needed, a fact that further encourages the search for new antimicrobial compounds from unexplored natural sources [1, 2]. The relatively little-known and very diverse groups of symbiotic microbes hold the promise of exciting discoveries to come. Few examples of defence mutualisms between social insects and microorganisms have been described in the literature, in which it has been demonstrated that social insects have developed mutually beneficial associations with microbes that provide colonies with antimicrobial agents [3]. Twelve termite species were collected in French Guiana from which 130 entomogenic microbes were isolated. A screening of all microbial EtOAc extracts was carried on pathogenic fungi (Candida albicans, C. parapsilosis, Aspergillus fumigatus and Trichophyton rubrum) and bacteria (Staphyloccocos aureus and Escherischia coli). Active extracts yielded to several active compounds, including a large proportion of previously undescribed ones. In particular, two strains of Pseudallescheria boydii have allowed us to isolate the antibacterial metabolites tyroscherin and N-methyl-tyroscherin, as well as a number of ovalicin analogs for which a biosynthetic pathway can be proposed. Interestingly, several strains of P. boydii have been isolated from several termite nests, and considering the very strong antibacterial potential of tyroscherins, it can be hypothesized that P. boydii may be symbiotically associated to several termite species in French Guiana. P. boydii metabolites can undoubtedly inspire the discovery of active antibacterial compounds.

Acknowledgements: This work has benefited from an “Investissement d'Avenir” grant managed by the ANR (CEBA, ref. ANR-10-LABX-25 – 01).

Keywords: Pseudallescheria boydii, symbiose, entomogen, termites, antimicrobial metabolites

References:

[1] Davies G. R., et al. (2013) CPT Pharmacometrics Syst. Pharmacol., 2: e70.

[2] Purvis A. Hector A. (2000) Nature 405: 212 – 219.

[3] Stow A., Beattie A. (2008) Brain Behav. Immun. 22: 1009 – 1013.