Isolation and characterisation of the antifungal activity of the cowpea defensin Cp-thionin II.

As a result of the rapidly growing human population, reducing post-harvest crop losses of cereals due to microbial pests has major importance. Plant defensins have the potential to fulfil these demands, being highly specific and efficient antimicrobial agents. Hence, this study aimed to extract and characterise a peptide from cowpea seeds and investigate its antifungal performance. After extraction and partial purification, N-terminal sequencing was used to identify the primary peptide in the extract as cowpea-thionin II. Antifungal activity in vitro was found against Fusarium culmorum (MIC = 50 μg/mL), but Aspergillus niger and Penecillium expansum showed an MIC > 500 μg/mL. The extract was resistant against heat treatment (100 °C, 15 min) but lost its antifungal activity in presence of cations (Na+, K+, Ca2+ and Mg2+, respectively). Membrane permeabilization of fungal hyphae was evident at 25 μg/mL, while induction of oxidative stress only had minor contribution to the antifungal performance. The extract did not induce haemolysis at all concentrations tested (up to 200 μg/mL). Finally, it was successfully used to protect stored wheat grains from fungal spoilage (determined via ergosterol content) when applied at 100 μg/mL. In conclusion, the defensin Cp-thionin II showed the potential for future application as food bio-preservative.