Synthesis of chitosan biocomposites loaded with pyrrole-2-carboxylic acid and assessment of their antifungal activity against Aspergillus niger.

A wide variety of chitosan (CS) biomaterials have been loaded with different antimicrobial agents to improve the activity of CS against phytopathogenic fungi. Recently, the antimicrobial activity of 1H-pyrrole-2-carboxylic acid (PCA) has been reported as a secondary metabolite of Streptomyces griseus, which was identified as the main bioactive compound in the biological control. However, it is sensitive to light and its activity against filamentous fungi has not yet been reported. The aim of the present research work was to evaluate the biological activity of CS-PCA biocomposites for the control of Aspergillus niger. CS-PCA biocomposites were obtained through nanoprecipitation. In vitro antifungal activity was determined by viability assay, spore germination, morphometric analysis of spores and hyphae, and the analysis of cellular components by fluorescence microscopy. CS-PCA showed an average size and Z potential of 502 ± 72 nm and + 54.7 ± 15 mV, respectively. Micrographs demonstrated well-distributed biocomposites with an apparently spherical shape. A new signal at 1473 cm-1 in the FT-IR spectrum of the CS-PCA biocomposite was observed, confirming the presence of PCA in the composition of the CS-PCA nanosystem. CS-PCA biocomposites reduced the spores' viability by up to 58%. Effects on fungi morphometry, observed as an increase in the spores' average diameter, swelling, distortion, and an increase in the branching of hyphae, were observed. Fluorescence analysis showed oxidative stress and membrane and cell wall damage, mainly at early growth stages. The inhibitory effect against CS-resistant fungi, such as A. niger, opens a door for the control of CS-sensitive fungi.