Cyanotoxins have been largely studied in planktonic and benthic cyanobacteria, but
microcystin (MCYST) production in epiphytic cyanobacteria has not been reported yet. The
present study reports for the first time the MCYST production in epiphytic cyanobacteria
on submerged macrophytes. During this study, four common submerged macrophytes in
eutrophic pond in Saudi Arabia were surveyed for the presence of toxic epiphytic cyanobacteria.
The results showed that chlorophyll-a and total biovolume of epiphytic cyanobacteria
differed significantly among submerged plants with highest values obtained in
Stratiotes aloides and lowest in Elodea canadensis. Epiphytic materials collected from
Ceratophyllum demersum and S. aloides had higher species diversities than materials
collected from E. canadensis and Myriophyllum verticillatum. The cyanobacteria, Merismopedia
tenuissima and Leptolyngbya boryana were recorded with a high abundance in
epiphytic materials collected from all submerged macrohpytes. Based on Enzyme-linked
immunosorbent assay (ELISA), these two species were found to produce MCYSTs
(MCYSTs) with concentrations of 1438 and 630 mg g1 dry weight, respectively. HPLC
analysis of the methanolic extracts of the two species showed that M. tenuissima extract
contained MCYST-RR and -LR/demethyl LR plus 3 minor unidentified MCYSTs, while
L. boryana extract contained MCYST-YR, -LR/demethyl LR, and 2 minor unidentified
MCYSTs. This study suggests that epiphytic species should be considered during monitoring
of toxic cyanobacteria in water sources.