In vitro effect of recombinant amaranth cystatin (AhCPI) on spore germination, mycelial growth, stress response and cellular integrity of Aspergillus niger and Aspergillus parasiticus

The inhibitory effect of recombinant amaranth cystatin (AhCPI) on the spore germination and growth of the mycotoxigenic fungus Aspergillus parasiticus and Aspergillus niger was investigated. AhCPI showed a concentration-dependent antifungal activity against both fungi. Differential effects were observed when fungi were treated with cystatin in two developmental stages. When AhCPI was added to young mycelium cultures of A. niger, it had a dramatic effect on mycelial growth compared with old mycelium cultures. On the contrary, there was no differential effect of AhCPI addition to either old or young mycelium of A. parasiticus. Furthermore, electron microscopic observations showed that cystatin caused important effects at the level of cell morphology and organelle integrity of both fungi. Additionally, A. parasiticus spores treated with AhCPI presented sensitivity to oxidative, osmotic and ionic stresses; in opposition, under same conditions, A. niger did not show sensitivity to any stressful agent. These results suggest that AhCPI antifungal activity might be related with damage to cell integrity, affecting the survival of the fungi. In addition, our evidences showed that fungal species respond dissimilarly to cystatin; however, such disparities can be used to the control of unwanted fungi.