Multiannual trend of microcystin production in the toxic cyanobacterium Planktothrix rubescens in Lake Garda (Italy)

ABSTRACT

Massive developments (blooms) of cyanobacteria represent a major concern in many natural and artificial waterbodies, because of the high levels of toxins that can be released into water. Microcystins, potent hepatotoxins, represent the most frequent toxins produced by cyanobacteria. The determination of the microcystins’ profile in waterbodies is important for determining the real toxic potential. We have investigated the evolution of the microcystins’ profile of Lake Garda (Italy) from both a qualitative and a quantitative point of view over a period of five years. We have also analysed possible correlations between toxin profile and selected environmental parameters. We found that a demethylated microcystin variant (RRdm) was always dominant but showing a cyclic trend, alternating periods in which it represented the only variant, and periods in which other variants were present (LRdm, HtyrRdm, RR, and LR). These changes are probably due to changes in chemotypes composition inside the resident Planktothrix rubescens population and do not seem to be exclusively linked to the considered environmental variables. Total microcystin concentrations were always low (in the ng L⁻¹ scale), and showed typical peaks in the metalimnetic layer during summer–autumn time of each year.

KEYWORDS:

• Lake Garda
• cyanobacteria
• Planktothrix rubescens
• cyanotoxins
• microcystins
• LC–MS
• environmental parameters

Acknowledgements

Investigations in Lake Garda were conducted in the framework of the LTER (Long Term Ecological Research) Italian network, site ‘Southern Alpine lakes', IT08-000-A (http://www.lteritalia.it/). This work was supported by PhD fellowships to S.S. from the Fondazione Edmund Mach. We thank the European Cooperation in Science and Technology COST Action ES1105 CYANOCOST for networking and knowledge transfer support. We are finally grateful to Mr. Andrea Zampedri and staff from ARPA Veneto (Giorgio Franzini) for their support in the field and laboratory activities.

Disclosure statement

No potential conflict of interest was reported by the authors.