Paper accepted: Synergistic antimicrobial activities of chitosan mixtures and chitosan-copper combinations

Today, the manuscript or our postdoctoral researcher Dr. Philipp Lemke and his former Master student Lena Jünemann has been accepted for publication in a Special Issue on “Synthetic and Natural Antifungals – Desirable and Hazardous Effects” of the “International Journal of Molecular Sciences”. Lena had conducted systematic investigations into the synergistic activity of chitosan oligomers and polymers which we had recently reported for the first time. She was able to corroborate this effect with more highly acetylated chitosans than before, showing that this is a more general effect which can be used to potentiate the antimicrobial and phytostimulatory activities of chitosans. Then, she and Philipp combined these chitosan mixtures with copper ions which possess known antifungal activity, eventually verifying another synergistic effect, this time between the chitosans and the copper ions. Copper-based fungicides have been used successfully in agriculture to protect crop plants from microbial infections, and they are indispensable even today, particularly in organic agriculture where alternatives are often lacking. However, to be effective, high copper concentrations are required, and this has resulted in copper build-up in many soils. Therefore, to preserve soil health which is all-important for the production of high-quality crops, the amount of copper allowed to be used per hectare is continuously being reduced by the regulatory authorities. Combinations of copper with environmentally safe agro-biologics such as chitosans, which might allow this reduction, have long been proposed but are difficult to realise because copper-chitosan mixtures tend to precipitate. The synergism we now describe allows us to work with low concentrations of both components, thus avoiding precipitation. So far, it works in the lab – now, we will need to make it work in the field, too. Then, this will have the potential to become an important step in our urgently needed transition to sustainable agriculture.