Effect of abiotic factors on the stability of chosen oligopeptides isolated from the freshwater cyanobacterium Woronichinia naegeliana

Abstract

Cyanobacterial blooms have a significant impact on water quality. Implementing appropriate treatment methods to remove cyanobacterial secondary metabolites requires assessing their stability. In contrast to cyanotoxins, the effect of abiotic factors on cyanopeptides has been poorly studied. The present study analysed the impact of pH, temperature, visible and ultraviolet (UV) radiation on the stability of chosen oligopeptides found in a freshwater cyanobacterium Woronichinia naegeliana bloom that frequently appears in drinking water reservoirs worldwide. The tested cyanopeptolin 1081 (CYA-1081) and anabaenopeptin 899 (ANB-899) were relatively stable at room temperature for 12 weeks regardless of pH. However, boiling (100 °C) for one hour affected the partial decomposition of the compounds in a pH-dependent manner; the highest decrease in the initial content of CYA-1081 to 47.0% was recorded at pH 9, while for ANB-899 to 42.4% at pH 3. The tested cyanopeptolin was resistant to visible radiation, but UV radiation in an acidic condition caused its degradation by 32.3%. Treatment of ANB-899 with visible or UV radiation for 3 h caused its partial decomposition with a maximum reduction of 40.4 and 70.8%, respectively, at acidic pH. The presented data provided information on factors affecting the cyanopeptides persistence and may be useful in the search for and development of effective methods of removing cyanobacterial metabolites.