Induction of diverse secondary metabolites in Aspergillus fumigatus by microbial co-culture

Irene Hallyburton,Alan T. Bull,Rakesh Santhanam,Mostafa E. Rateb,Wael E. Houssen,Michael Goodfellow,Rainer Ebel,Marcel Jaspars

doi:10.1039/c3ra42378f

Abstract

An established culture of Aspergillus fumigatus MBC-F1-10 proved to be very receptive to external stimuli and reacted with the production of secondary metabolites which were undetectable when the fungus was grown under standard conditions. Firstly, co-cultivation with the type strain of Streptomyces bullii, an isolate from hyper-arid Atacama desert soil, led to the isolation of ergosterol 1, seven metabolites belonging to the diketopiperazine alkaloids; brevianamide F 2, spirotryprostatin A 3, 6-methoxy spirotryprostatin B 4, fumitremorgin C and its 12,13-dihydroxy derivative (5–6), fumitremorgin B 7, and verruculogen 8, in addition to 11-O-methylpseurotin A 9 and its new isomer 11-O-methylpseurotin A210. In an independent experiment, addition of N-butyryl-DL-homoserine lactone to the culture medium led to the production of emestrins A and B (11–12). Neither microbe produced these compounds when cultured alone. The structures of all compounds were elucidated using NMR spectroscopic techniques and mass spectrometric analysis. The isolated compounds were tested for their potential antibacterial and antiprotozoal activities.

Highlights

An established culture of Aspergillus fumigatus MBC-F1-10 proved to be very receptive to external stimuli and reacted with the production of secondary metabolites which were undetectable when the fungus was grown under standard conditions
Streptomyces sp. strain C2, which was recently proposed as the type strain of Streptomyces bullii,17 was one of several putatively novel Streptomyces strains from the Atacama Desert included in our chemical screening programme
The fungus was purified by subculture on malt extract agar plates, and identified as Aspergillus fumigatus based on the comparison of the sequence of its ITS region with previously published sequences obtained from GenBank

Summary

Introduction

Microbial secondary metabolites have been considered one of the best resources for drug discovery.1 Up to early 2013, more than 42 000 natural compounds have been characterized from microorganisms and higher fungi.2 Parallel to this increase in the rate of isolation of new microbial natural products, the rate of re-isolation of known secondary metabolites has increased significantly in the past few years.3 Given the fact that microorganisms naturally interact with each other, simulating microbial competition for nutrition and space is regarded as a major route for the induction of bioactive secondary metabolites.4 mimicking the natural microbial environment, cultivation of two different microbial strains together in one culture vessel (i.e., competing co-culture) allows direct interaction between these microbes which mayMost previous co-culture experimental studies reported an increase in biological activity without the identification of the secondary metabolites responsible for this effect, confirmed the induction of antibiotic biosynthesis but not the induction of specific metabolic pathways or increased yields of previously described metabolites.7,8 the induction of a previously unexpressed biosynthetic pathway leading to the production of new secondary metabolites in response to coculture is less often described in the literature. These results prompted us to re-cultivate the bacterial sterile ferment on ISP2 agar plates with incubation at 30 uC, which led to the isolation of a pure culture of strain C2 in addition to an unknown fungal strain, labelled MBC-F1-10.

Results

Conclusion