Toxin variability during the cell cycle of the dinoflagellate Alexandrium fundyense

Abstract

Cultures of the toxic dinoflagellate AlexandriumfundyenseBalech were subjected to conditions that induced two synchronized divisions over a period of 48 h. Before, during, and after this in:erval, toxin content, toxin composition, and several other physiological parameters were monitored every 2 h for 94 h. Toxin production was discontinuous, induced by light, and always occurred during a defined time frame within Ihe G, phase of the cell cycle. Specific toxin production rates were positive for a period of -8-10 h in early G, and dropped to zero for the remainder of the interphase and mitosis. Analysis of toxin composition showed that cellalar concentrations of all the saxitoxin derivatives followed a similar pattern of increase, stabilization, and decrease throughout one generation time. A putative sequence of interconversions between the derivatives could be established, with C2 as the first compound to appear. Division of a subset of the population during the first 24 h of the experiment and the ensuing total synchrony of the culture suggest the existence of two transition points in the cell cycle of this dinoflagellate. The first transition point, at the beginning of G,, is light-dependent and holds the cells in a Go-like period. The second block point at the end of G, is size-dependent and arrests the cells in G,. Mre propose a model of the cell cycle of A. fundyense in which progression through the cell cycle can be arrested at two different transition points located in G, and toxin production is induced by light during G,. The restriction 0:' toxin production to a relatively short segment of the cell cycle provides a tool for comparing cells that are and are not synthesizing toxin.

Identification and Characterization of Three Differentially Expressed Genes, Encoding S -Adenosylhomocysteine Hydrolase, Methionine Aminopeptidase, and a Histone-Like Protein, in the Toxic Dinoflagellate Alexandrium fundyense

“…DD of mRNA was applied to synchronized cells of A. fundyense in different cell cycle stages (Fig. 2B) and while toxin production was on or off (52). Two samples were drawn during G 1 , one while toxin production was active (Fig.…”

“…A series of studies with synchronized cultures of Alexandrium fundyense has further shown that STX is accumulated during a discrete time period localized in the G 1 phase of the cell cycle ( Fig. 1) (52). The combination of these two factors, nuclear genes and discontinuous toxigenesis, gave rise to the hypothesis that STX biosynthesis could be regulated at the transcriptional level, with the genes responsible for toxin production being activated in a cyclic pattern.…”

The Biosynthesis of Polyketide Metabolites by Dinoflagellates

“…In this case, the DD patterns were identical for G 1 , S, and G 2 phases, which permitted the identification of differentially expressed bands. Saxitoxin has been shown to accumulate during a discrete time period in the G1 phase of the cell cycle (Taroncher-Oldenburg et al, 1997). Thus, the focus was to identify genes expressed or suppressed in early G 1 when compared with the remainder of the cell cycle.…”

Physiological and behavioral diagnostics of nitrogen limitation for the toxic dinoflagellate Alexandrium fundyense

“…Therefore, toxin composition has been used as a chemotaxonomic character that distinguishes isolates of Alexandrium from different geographic regions . Only recently have changes in Alexandrium toxin composition been observed during growth in batch culture (late stationary phase) ), over the cell cycle and in N-and P-limited semi-continuous cultures (Anderson et al 1990b;Taroncher-Oldenburg et al 1997). …”