Screening of plant extracts for a microcosm in vivo test of inhibition of the toxic bloom-forming cyanobacteria Chrysosporum ovalisporum

Freshwater eutrophication is an increasing ecological and public health concern. One of the major consequences of eutrophication is the formation of harmful algal blooms (HABs), a rapid population increase and accumulation of microorganisms, namely algae and cyanobacteria. In this project, we aim to investigate a nature based solution to this environmental hazard. Our approach consisted in the evaluation of the potential of aquatic plants to control the growth and viability of Chrysosporum ovalisporum, a cyanobacteria species associated with HABs and that produces toxic metabolites such as cylindrospermopsin. First, we carried out a screening with different plant species – Iris pseudacoros, Typha latifolia, Sparganium erectum, Alisma plantago-aquatica, Alisma lanceolatum, Nasturtium officinale, Landoltia punctata, Lemna minor and Wolffia arrhiza – for the allelopathic effect of their extracts on this cyanobacteria. For this purpose, methanol/water (70:30, v:v) mixture extracts were prepared and tested, at various concentrations, in C. ovalisporum cultures. Exposure to L. punctata extracts at the highest concentration tested (2 mg L−1) showed significant cellular abundance inhibitory effects on C. ovalisporum. Secondly, a microcosm system was assembled to evaluate the effects of co-growth of C. ovalisporum and L. punctata. In this experiment, we tested the effect of the presence of this plant on C. ovalisporum cell abundance, under a nutritional surplus and equivalent cyanobacterial light exposure in between test and control groups. The results confirmed the allelopathic effect of L. punctata on C. ovalisporum. This work demonstrates that the allelopathic properties of aquatic plants could be exploited to control the growth of harmful algae, and could be used to develop novel, eco-friendly and practical solutions, for treatment of water contaminated with C. ovalisporum.