Abstract
Chitosan has been tested as a coagulant to remove cyanobacterial nuisance. While its coagulation efficiency is well studied, little is known about its effect on the viability of the cyanobacterial cells. This study aimed to test eight strains of the most frequent bloom-forming cyanobacterium, Microcystis aeruginosa, exposed to a realistic concentration range of chitosan used in lake restoration management (0 to 8 mg chitosan L−1). We found that after 1 h of contact with chitosan, in seven of the eight strains tested, photosystem II efficiency was decreased, and after 24 h, all the strains tested were affected. EC50 values varied from 0.47 to > 8 mg chitosan L-1 between the strains, which might be related to the amount of extracellular polymeric substances. Nucleic acid staining (Sytox-Green®) illustrated the loss of membrane integrity in all the strains tested, and subsequent leakage of pigments was observed, as well as the release of intracellular microcystin. Our results indicate that strain variability hampers generalization about species response to chitosan exposure. Hence, when used as a coagulant to manage cyanobacterial nuisance, chitosan should be first tested on the natural site-specific biota on cyanobacteria removal efficiency, as well as on cell integrity aspects.
Highlights
Cyanobacteria play an essential role in oxygen production, being responsible for half of the ocean’s primary production [1]
Our present study aims to extend the knowledge of possible side effects caused by chitosan on the cyanobacterium, Microcystis aeruginosa
Considering the effect of chitosan on the Photosystem II (PSII) efficiency, we could divide the M. aeruginosa strains based on their response into two groups: (1) the strains that have a delayed response to chitosan (MiRF-1, PCC Toxins and PCC 7820) and (2) the more sensitive strains with an earlier3 of response
Summary
Cyanobacteria play an essential role in oxygen production, being responsible for half of the ocean’s primary production [1]. Cyanobacterial species may form intense blooms under certain conditions, which have severe impacts on water bodies, such as increased water turbidity, nocturnal depletion of oxygen, fish kills, and malodour [2,3]. Cyanobacteria can produce toxins that are harmful to aquatic and terrestrial organisms, including humans and dogs, impeding water bodies use for recreational activities, drinking water production, fishing, and agricultural use and, causing severe economic losses [4,5,6,7,8]. The main cause of cyanobacterial blooms is the excess of nutrient supply to waterbodies (eutrophication) [9]. The classical and most straightforward approach is to reduce the external
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