Mycelial interaction is a basic method for determining the antagonistic ability and tolerance to antagonism among fungi. It has been used as a tool to be screening of potential biological control agents [20, 21].
Different methods have been used to understand the interactions between cultures as colony interactions, hyphal interference, non-volatile metabolites, volatile metabolites [20]. Among them is the dual culture method that shows the interactions between two organisms involving the stimulation or inhibition of their growth [22]. In previous study [19] we used this method, described by Rahman et al. [23], to analyze the antagonistic effect of P. lilacinum on the growth of one S. brasiliensis isolate. In current study, we proved its usefulness and practicality to evaluate the antagonistic property of more P. lilacinum isolates from soil.
P. lilacinum has already been described as a biocontrol agent [24, 25], with ability to inhibit the growth of other fungi [26, 27], with and without physical contact between their colonies [24].
When Costa et al. [19] studied the interaction of some soil isolates of P. lilacinum with S. brasiliensis, the main causal agent of the sporotrichosis in Brazil, it was possible to note that some P. lilacinum isolates antagonized S. brasiliensis growth showing different degrees of inhibition. However, of the ten P. lilacinum isolates tested by these authors the percentage of inhibition was not considered high (8 to 25%) when compared of the percentage of inhibition (83.3%) of the P. lilacinum strain against Botrytis cinerea [28]. Therefore, we decided to look for new isolates from soil of the same region (Atlantic Forest region) also situated in the state’s sporotrichosis transmission belt in Rio de Janeiro, Brazil, that could have greater inhibition capacity when tested against pathogenic species of the genus Sporothrix. There is no record of an evaluation of the antagonistic activity of P. lilacinum against members of clinical clade (S. schenckii, S. brasiliensis, S. globosa, and S. luriei) and environmental clade (S. mexicana, S. chilensis, and S. pallida) of the genus Sporothrix.
Our results were similar to those described by Costa et al. [19] regarding the number of isolates from soil identified as P. lilacinum. Once again, we demonstrated the predominance of this species over other saprophytic species in an area considered to be the transmission sporothrichosis. We verified, as well as Costa et al. [19] that there is inhibition variation dependent on the P. lilacinum isolates. This same behavior has already been seen for other fungi in analyzes of antagonistic potential [23, 29, 30].
We also observed, for one isolate of P. lilacinum (RPL5), inhibition value of 41.1% and 61.5% of the growth of S. brasiliensis and S. globosa, respectively the second and third more frequent infectious agents of the disease [31]. In as much as S. brasiliensis is the main cause of epidemic outbreaks in Brazil, justified by its greater virulence and ability to evade the immune response [32], this isolate RPL5 may be important for future studies.
Additionally, was seen that Sporothrix spp belonging to the “pathogenic clade” (S. schenckii sensu stricto, S. brasiliensis, S. globosa and S. luriei) [33], classically more virulent species, had its growth inhibited by most of the P. lilacinum isolates, except for S. schenckii and S. luriei, inhibited by 4 and 3 P. lilacinum isolates, respectively. The other species from the environmental clade, considered of low virulence, such as S. pallida and S. chilensis, had their growth inhibited by only 1 of the P. lilacinum isolates, with exception of S. mexicana, inhibited by 9 of P. lilacinum isolates. On the other hand, we found an isolate (RPL2) capable of inhibiting all pathogenic Sporothrix spp., which make us again very interested in further studies in the search for bioactive compounds.
According to Boddy and Hiscox [34] the production of secondary metabolites by fungi can alter a series of physiological mechanisms of the other fungi, and it may be one of the possible mechanisms for antagonism between them. As previously described P. lilacinum can produce secondary metabolites such as leucinostatins, acremonidins, acremoxanthones, paecilomide, pyrones, phomoligols and others [35]. Leucinostatin Z, a new antifungal lipopeptaibol, was described by Liu et al. [28], when studying cocultures of P. lilacinum and Botrytes cinerea. For all records of diversity in secondary metabolites with bioactivity produced by P. lilacinum isolates and antagonistic effects between it and other fungi, mainly those described in this study for Sporothrix spp. reinforce our interest in identifying and studying the biological actions of the metabolites with bioprospecting potential involved in this interaction hereafter.