Sparking Fungal Activity with Bacterial Components: Can co-culture with bacterial components induce antibacterial activity in New Zealand fungi?

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum β-lactamase (ESBL) and carbapenemase-producing bacteria cause deadly multi-drug resistant infections, against which most of the current antibiotics we use are ineffective. To replenish our banks of antibiotics, the biodiscovery of natural products in the form of fungi secondary metabolites is attractive and has resulted in several interesting antibacterial compounds. The OSMAC (One Strain, Many Compounds) approach has been undertaken to induce secondary metabolite production by fungi. More recently, bacterial components have also been used to activate fungal secondary metabolite function. For this project, I investigated whether co-culturing New Zealand fungi with bacterial components such as lipopolysaccharide (LPS) and lipoteichoic acid (LTA), or autoclaved bacteria would impact fungal secondary metabolite production. I made use of bioluminescent derivatives of Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa, and S. aureus to detect any antibacterial activity by the co-culture supernatant. As these tagged bacteria only glow when they are alive, bioluminescence is a sensitive, rapid, and non-destructive way to measure bacteria metabolism and viability. Finally, I used liquid chromatography coupled with mass spectrometry (LC-MS) to help elucidate changes in the secondary metabolite profile of the fungi. I screened 30 New Zealand fungi, a mixture of previously tested and untested isolates, and identified eight that were active under at least one of the conditions I grew them under. Of these fungi, the addition of autoclaved bacteria induced antibacterial activity in Neofusicoccum cryptoaustrale and Heterobasidion araucariae, and the presence of LTA potentially enhanced antibacterial activity of Stropharia rugosoannulata. All other active isolates displayed activity both in the presence and absence of the additives, with some additive conditions prolonging or enhancing antibacterial activity. Four isolates retained active fractions after LC-MS allowing me to identify two known antibacterial compounds, patulin from Penicillium expansum and piptamine from Stropharia rugosoannulata. While I did not discover any novel antibacterial compounds during my studies, my findings confirm the potential for bacterial components to induce changes in fungal secondary metabolite production, and highlight the utility of LC-MS as a complementary dereplication tool.