Secondary metabolites produced during Aspergillus fumigatus and Pseudomonas aeruginosa biofilm formation

In Cystic Fibrosis (CF), mucus plaques are formed in the patient's lung, which creates a hypoxic condition and a propitious environment for colonization and persistence of many microorganisms. There is clinical evidence showing that Aspergillus fumigatus can co-colonize/infect CF patients with Pseudomonas aeruginosa, which has been associated with lung function decline. Several reports have showed that P. aeruginosa produces several compounds with inhibitory and anti-biofilm effects against A. fumigatus in vitro; however, little is known about the fungal compounds produced in counterattack. In this work we annotated fungal and bacterial secondary metabolites (SM) produced in mixed biofilms in normoxia and hypoxia conditions. We detected nine SMs produced by P. aeruginosa. Phenazines and different analogs of pyoverdin were the main compounds produced by P. aeruginosa, and their secretion were increased by the fungal presence. The roles of the two operons responsible for phenazines production (phzA1 and phzA2) were also investigated and the results showed that phzA1 and ΔphzA2 mutants are able to produce partial sets of phenazines when in hypoxia and in the presence of the fungus. We detected a total of 20 SMs secreted by A. fumigatus either in monoculture or in co-culture with P. aeruginosa. All these compounds are secreted during biofilm formation either in normoxia or hypoxia. However, only eight compounds (demethoxyfumitremorgin C, fumitremorgin, ferrichrome, ferricrocin, tricetylfusigen, gliotoxin, gliotoxin E, and pyripyropene A) were detected detected during the biofilm formation by the co-culture of A. fumigatus and P. aeruginosa upon both normoxia and hypoxia conditions. Overall, we showed how diverse is SM secretion during A. fumigatus and P. aeruginosa mixed culture and how this can affect biofilm formation both in normoxia and hypoxia.