Sterol biosynthesis in the harmful marine dinoflagellate, Karenia brevis: Identification of biosynthetic intermediates produced during exposure to the fungicide fenpropidine

Abstract

Karenia brevis is a harmful marine dinoflagellate that forms yearly blooms in the Gulf of Mexico. Under normal growth conditions, K. brevis forms two predominant sterols (24R)-4a-methyl-5a-ergosta-8(14),22-dien-3b-ol (gymnodinosterol) and its 27-nor isomer (brevesterol). At the current time, there are no published studies concerning the biosynthesis of these two sterols. We have therefore undertaken experiments in which K. brevis was exposed to the fungicide fenpropidine, an inhibitor of the D 14 -reductase and the D 8→7 -isomerase that operate in sterol biosynthesis in both fungal and plant systems. Such exposure to fenpropidine has produced two, tri-unsaturated intermediates. The identifications of these two K. brevis sterol biosynthesis intermediates, via gas chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy techniques, were 4a-methyl-5a-ergosta-8,14,22-trien-3b-ol and 5a-ergosta-8,14,22-trien-3b-ol.

Sterols of Testudodinium testudo (formerly Amphidinium testudo): Production of the Δ8(14) sterol gymnodinosterol and chemotaxonomic relationship to the Kareniaceae

“…Their retention times matched those of the T. testudo sterols, and, as evidenced in Figure 1, their mass spectra were also identical. Thus, we conclude that T. testudo produces a Δ 8( 14) sterol common to the Kareniaceae, and its presumed biosynthetic intermediate (see Leblond et al, 2011 for discussion on the biosynthesis of gymnodinosterol and brevesterol in K. brevis), rather than a Δ 8( 14) sterol specific to Amphidinium. It should be noted, however, that while the genus Amphidinium is one of the few dinoflagellate taxa where the sterol composition can be dominated by Δ 8( 14) sterols, exceptions include the photosynthetic Amphidinium massartii Biecheler, which has instead been observed to reside in a cluster of dinoflagellates which produce cholesterol as a dominant sterol in the absence of Δ 8( 14) sterols (Leblond et al, 2010), and heterotrophic Amphidinium longum Lohmann, which has also been observed to produce cholesterol (Chu et al, 2009).…”

“…Mass spectra of gymnodinosterol and 4α‐methyl‐5α‐ergosta‐8,14,22‐trien‐3β‐ol are shown in Figure 1, along with mass spectra of these same sterols from Karenia brevis (C.C.Davis) Gert Hansen & Moestrup. While spectra for these sterols from K. brevis were originally published in Leblond and Chapman (2002) and Leblond et al (2011), respectively, they are included again here as run on the same instrument as the T. testudo sterols. Their retention times matched those of the T. testudo sterols, and, as evidenced in Figure 1, their mass spectra were also identical.…”