Toxic cyanobacteria in a water reservoir in Sicily: Considerations for monitoring programs and risk assessment

During the last century several water reservoirs have been built for drinking and irrigation purposes in Sicily, the largest island in the South of Italy. Over the years some of them have been reported to be affected by cyanobacteria blooms, but monitoring programs have been discontinuous. A quarterly two years survey of cyanobacteria (CB) and cyanotoxins (CTX) in the main reservoirs started in 2016, in order to assess the possible risks for the exposed population. All lakes but one have a CB community and CTX concentrations within acceptable ranges. Here we present the preliminary results of the critic one, Lake Disueri, with a surface of 1,85 km2 and a 31 and 15.2 m maximum/average depth, which is strongly reduced during persistent dryness. Blooms of CB species have been detected for the first time during summer 2017 (characterized by very high temperature in a very dry period). Microcystis sp. and Cylindrospermopsis raciborskii were detected in July (108 and 107 cell/L, respectively) and by mid- Aug were replaced by Anabaenopsis sp. and Plankthotrix rubescens, still growing in mid-Sept were (107 and 106 cell/L, respectively). MCs concentrations were low, in agreement with the lack of qualitative amplification of the mcyE gene (demonstrated by a 370 bp product in the two positive controls), indicating that the MC-producing fraction within CB population was low. The amplification of both cyrJ (~ between 550 and 600 bp) and stxB (~ 270-300 bp + a high mw variable band) occurred in all samples, concurrently with high density of C. raciborskii and Anabaenopsis sp.. Therefore, a potential ability to produce CYN and STX could be assumed for these samples, even if at the moment no positive control was available. The detection of MC levels allowed to assess a very low risk for the population and livestock using the lake’s water, while by the number of cell the risk would have been considered much higher. The use of a simple qualitative PCR is a good tool to investigate the presence of potentially toxic CB, and to check for possible new toxin production population. The presence of cyrJ and stxB, once confirmed, could indicate the presence of a Cylindrospermopsis strain with potential production of CYN and STX, for the first time in Italy and Europe, and of a Anabaenopsis strain producing CYN and STX.