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A clonal culture of a Vietnamese strain of Alexandrium minutum, AlexSp17, was subjected to different salinity treatments to determine the growth and toxin production of this strain that produces a novel toxin analogue, deoxy GTX4-12ol. The experiment was carried out in batch cultures without pre-acclimatization at seven salinity treatments from 5 to 35 psu, under constant temperature of 25°C, illumination of 140 μmol photon m s, and 12:12 light/dark photoperiod. The strain grew in all salinity treatments, with optimum growth at 10-15 psu. However, the specific growth rate (0.2 day) was lower than those reported in Malaysian strains and other strains from different geographical areas. The optimum range of salinity for the growth of this species agreed with field observations of the locality of origin. No significant change in toxin profiles was observed at different salinities. The cellular toxin quota, Qt, was not affected by the salinity-dependent growth rate. The toxin GTX4-12ol is presumed to be a transformation product of GTX4 from specific cellular reductase enzymes. Further investigation at the molecular level of toxin biosynthesis and subcellular enzyme activities is needed to provide insight in the production of this unique toxin analogue. [ABSTRACT FROM AUTHOR]

While there is increasing evidence that marine bacteria are involved in the production of paralytic shellfish toxins in algal blooms, the exact roles of the bacteria and microalgae have proved elusive. A novel experimental approach to this problem involved incubating parallel cultures of toxin producing Alexandrium minutum Anokoha A in the dark and in a natural daylight cycle. High-performance liquid chromatography was used to measure paralytic shellfish toxins while bacterial growth was monitored by culture on high- and low-nutrient agar media. After a 22-day incubation period in the dark, A. minutum Anokoha A failed to produce saxitoxin while parallel light-grown cultures produced 1.17 μg per 10,000 algal cells. However, both dark- and light-grown cultures showed comparable gonyautoxin production. Copiotrophic and oligotrophic algal-associated bacteria showed similar growth patterns over the incubation period except that a dip in bacterial numbers corresponded to a peak in algal numbers in the light-grown cultures. It appears that inhibition of photosynthesis resulted in changes in the toxin profile of A. minutum Anokoha A. When used with other methods, this approach may help to elucidate the algal–bacterial-toxin connection. [ABSTRACT FROM AUTHOR]

Effects of nitrogen to phosphorous (N/P) ratios of two nitrogen sources (nitrate and ammonium) on growth and toxin production of a tropical estuarine dinoflagellate, Alexandrium minutum Halim, were examined using a strain isolated from a bloom at Tumpat Estuary, Malaysia in September 2001. Experiments were carried out in batch cultures, using either nitrate (N-NO3) or ammonium (N-NH4) as the nitrogen source at a constant amount, and with initial N/P ratios ranging from 5 to 500. Cell density, residual N and P in the medium, cellular toxin quota ( Qt), and toxin composition were analyzed throughout the growths. Our results showed that cell densities and growth rates of A. minutum were severely suppressed under high N/P ratios (>100) in both N-NO3 and N-NH4 treatments. Cells tended to be larger at lower growth rate and P-limited cultures. Toxin profile was relatively constant throughout the experiments, with GTX4/GTX1 as the dominant toxin congeners. Cellular toxin quota ( Qt) increased with elevated N/P ratios in both N-NO3 and N-NH4 treatments. Toxin production rate, Rtox, however was enhanced in N-NH4-grown cultures when P was limited, but showed no difference between N-NO3- and N-NH4-grown cultures when P was replete. Our results clearly showed that N/P ratios as well as the nitrogen compounds not only affected the growth of A. minutum, but also the cellular toxin quota and its toxin production rate. [ABSTRACT FROM AUTHOR]

Toxic dinoflagellates are important in natural ecosystems and are ofglobal economic significance because of the impact of toxic blooms onaquaculture and human health. Both the organisms and the toxins they producehave potential for biotechnology applications. We investigated autotrophicgrowth of a toxic dinoflagellate, Alexandrium minutum, inthree different high biomass culture systems, assessing growth, productivityandtoxin production. The systems used were: aerated and non-aerated2-L Erlenmeyer flasks; 0.5-L glass aerated tubes; anda 4-L laboratory scale alveolar panel photobioreactor. A range ofindicators was used to assess growth in these systems. Alexandriumminutum grew well in all culture conditions investigated, with amarked increase in both biomass and productivity in response to aeration. Thehighest cell concentration (4.9 × 105 cellsmL−1) and productivity (2.6 ×104cells mL−1d−1) was achieved inthe aerated glass culture tubes. Stable growth of A.minutum in the laboratory scale alveolar panel photobioreactor wasmaintained over a period of five months, with a maximum cell concentration of3.3 × 105 cells mL−1, a meanproductivity of 1.4 × 104 cells mL−1d−1, and toxin production of approximately 20μg L−1 d−1 with weeklyharvesting. [ABSTRACT FROM AUTHOR]