Retinoid compounds associated with water blooms dominated by Microcystis species

•Retinoid-like activity and retinoic acids found in water and cyanobacteria from lakes.•Studied independent water bodies with bloom dominated by Microcystis aeruginosa.•Retinoid-like activity up to 2838ngREQ/gdm in all cyanobacterial biomasses.•Retinoid-like activity up to 28.7ngREQ/L in some surrounding waters.•ATRA and 9-cis RA mostly contributed relatively little to the total REQs. Retinoic acids play a critical role in vital physiological processes and vertebrate development, and their derivatives can be produced by some cyanobacterial species into surface waters. This study presents important environmentally-relevant information on total retinoid-like activity of field cyanobacterial biomasses and their surrounding waters. Intracellular and extracellular levels of total retinoid-like activity and retinoic acids have been investigated at a set of independent sites with the occurrence of water bloom dominated by widespread species Microcystis aeruginosa. Twelve samples of biomass and surrounding water from seven localities affected by blooms were studied in comparison with samples from M. aeruginosa laboratory cultures. The method for biomass extraction was optimized and final extracts and samples of surrounding water concentrated by solid phase extraction were assessed using in vitro reporter gene bioassay and chemical analyses for all-trans-retinoic acid (ATRA), 9-cis retinoic acid (9-cis RA) and microcystins RR, LR and YR. Methanol was the most efficient solvent for the extraction of compounds with retinoid-like activity. An in vitro bioassay with the P19/A15 transgenic cell line revealed retinoid-like activity in all cyanobacterial biomasses in the range of 356–2838ng of retinoid acid equivalents (REQ)/g dry mass (dm), while only three of surrounding water samples exhibited detectable retinoid-like activity, in the range of 12.8–28.7ngREQ/L. Microcystins were detected in all samples, but they elicited no detectable retinoid-like activity up to 10mg/L. Chemical analyses detected concentrations up to 340ng/gdm of all-trans-retinoic acid (ATRA) and 84ng/gdm 9-cis retinoic acid (9-cis RA) in bloom extracts, and up to 19ng/L ATRA and 2.2ng/L 9-cis RA in surrounding water. In most samples, ATRA and 9-cis RA contributed relatively little to the total REQs, which indicates the presence of significant amounts of other compounds with retinoic acid receptor-mediated modes of action. The impact of retinoid-like cyanobacterial metabolites could be of importance