The reversible effect of flow on the morphology of ceratocorys horrida (PERIDINIALES,DINOPHYTA)*

Most cells experience an active and variable fluid environment, in which hydrodynamic forces can affect aspects of cell physiology including gene regulation, growth, nutrient uptake, and viability. The present study describes a rapid yet reversible change in cell morphology of the marine dinoflagellate Ceratocorys horrida Stein, due to fluid motion. Cells cultured under still conditions possess six large spines, each almost one cell diameter in length. When gently agitated on an orbital shaker under conditions simulating fluid motion at the sea surface due to light wind or surface chop, as determined from digital particle imaging velocimetry, population growth was inhibited and a short‐spined cell type appeared that possessed a 49% mean decrease in spine length and a 53% mean decrease in cell volume. The reduction in cell size appeared to result primarily from a 39% mean decrease in vacuole size. Short‐spined cells were first observed after 1 h of agitation at 20°C; after 8 to 12 d of continuous agitation, long‐spined cells were no longer present. The morphological change was completely reversible; in previously agitated populations devoid of long‐spined cells, cells began to revert to the long‐spined morphology within 1 d after return to still conditions. During morphological reversal, spines on isolated cells grew up to 10 μm·d^?1. In 30 d the population morphology had returned to original proportions, even though the overall population growth was zero during this time. The reversal did not occur as a result of cell division, because single‐cell studies confirmed that the change occurred in the absence of cell division and much faster than the 16‐d doubling time. The threshold level of agitation causing morphology change in C. horrida was too low to inhibit population growth in the shear‐sensitive dinoflagellate Lingulodinium polyedrum. At the highest level of agitation tested, there was negative population growth in C. horrida cultures, indicating that fluid motion caused cell mortality. Small, spineless cells constituted a small percentage of the population under all conditions. Although their abundance did not change, single‐cell studies and morphological characteristics suggest that the spineless cells can rapidly transform to and from other cell types. The sinking rate of individual long‐spined cells in still conditions was significantly less than that of short‐spined cells, even though the former are larger and have a higher cell density. These measurements demonstrate that the long spines of C. horrida reduce cell sinking. Shorter spines and reduced swimming would allow cells to sink away from turbulent surface conditions more rapidly. The ecological importance of the morphological change may be to avoid conditions that inhibit population growth and potentially cause cell damage.     

INFLUENCE OF PHOSPHORUS LIMITATION ON TOXICITY AND PHOTOSYNTHESIS OF ALEXANDRIUM MINUTUM (DINOPHYCEAE) MONITORED BY IN‐LINE DETECTION OF VARIABLE CHLOROPHYLL FLUORESCENCE1

The effects of phosphorus (P) limitation on growth, toxicity, and variable chl fluorescence of Alexandrium minutum were examined in batch culture experiments. Cell division was greatly impaired in P‐limited cultures, but P spiking of these cultures after 9 days stimulated high levels of cell division equivalent to P‐replete cultures. The cellular concentration of paralytic shellfish toxins was consistent over the growth cycle of control cultures from lag phase into logarithmic growth phase, with toxins repeatedly lost to daughter cells during division. The low level of cell division in P‐limited cultures resulted in a 10‐fold increase of cellular toxin compared with controls, but this dropped upon P spiking due to increased rates of cell division. The history of phosphorus supply had an important effect on toxin concentration, with the P‐limited and the P‐spiked cultures showing values 2‐fold higher than the P‐replete cultures. Toxin profiles of the A. minutum strain used in these experiments were dominated by the N₁‐hydroxy toxins, gonyautoxins (GTX) GTX1 and GTX4, which were approximately 40 times more abundant than their analogues, GTX2 and GTX3, in P‐limited cultures. The dominance of the N₁‐hydroxy toxins increased significantly in control cultures as they advanced through logarithmic growth. In‐line measurements of the variable chl fluorescence of light‐adapted cells indicated consistent photochemical efficiency under P‐replete conditions. P limitation induced a drop in fluorescence‐based photochemical efficiency that was reversible by P spiking. There was an inverse linear relationship between in‐line fluorescence and cell toxin quota (r = ?0.88). Monitoring fluorescence in‐line may be valuable in managing efficient biotechnological production of toxins.     

MECHANISMS OF FLUID SHEAR‐INDUCED INHIBITION OF POPULATION GROWTH IN A RED‐TIDE DINOFLAGELLATE1

Net population growth of some dinoflagellates is inhibited by fluid shear at shear stresses comparable with those generated during oceanic turbulence. Decreased net growth may occur through lowered cell division, increased mortality, or both. The dominant mechanism under various flow conditions was determined for the red‐tide dinoflagellate Lingulodinium polyedrum (Stein) Dodge. Cell division and mortality were determined by direct observation of isolated cells in 0.5‐mL cultures that were shaken to generate unquantified fluid shear. Larger volume cultures were exposed to quantified laminar shear in Couette‐flow chambers (0.004–0.019 N·m ^{? 2} shear stress) and to unquantified flow in shaken flasks. In these larger cultures, cell division frequency was calculated from flow cytometric measurements of DNA·cell^?1. The mechanism by which shear inhibits net growth of L. polyedrum depends on shear stress level and growth conditions. Observations on the isolated cells showed that shaking inhibited growth by lowering cell division without increased mortality. Similar results were found for early exponential‐phase cultures exposed to the lowest experimental shear stress in Couette‐flow chambers. However, mortality occurred when a late exponential‐phase culture was exposed to the same low shear stress and was inferred to occur in cultures exposed to higher shear stresses. Elevated mortality in those treatments was confirmed using behavioral, morphological, and physiological assays. The results predict that cell division in L. polyedrum populations will be inhibited by levels of oceanic turbulence common for near‐surface waters. Shear‐induced mortality is not expected unless shear‐stress levels are unusually high or when cellular condition resembles late exponential/stationary phase cultures.     

Laboratory evaluation of floating marine plastic debris as a potential vector for transportation of the harmful benthic dinoflagellate Fukuyoa koreansis

Marine plastic debris (MPD) can significantly impact marine ecosystems because it can function as a dispersal vector for organisms, including toxic and alien species. We performed laboratory experiments to assess the possible function of MPD as a dispersal vector for the harmful epiphytic dinoflagellate Fukuyoa koreansis. Specifically, we monitored growth of these cells under 6 conditions: no MPD (control; with or without agitation), with polyethylene (PE) film (sheet-like MPD; with or without agitation), and with polypropylene (PP) rope (cylindrical MPD; with or without agitation). Growth without agitation was not significantly different between experimental groups (p > 0.05, χ² = 0.228, Kruskal-Wallis test), indicating that the presence of MPDs had no significant effect on growth of F. koreansis under non-agitating conditions. After 15 days, growth without MPD was 25-fold greater without agitation than with agitation (150 ± 42 cells mL^-1 vs. 6 ± 1 cells mL^-1). When grown with both floating MPDs and agitation, 78 ± 1 % of the cells were attached to the MPD, which was 4-times greater than when they were grown without agitation. These results suggest that MPD or another attachment substrate is essential for the growth of F. koreansis in an unstable water mass, and that MPD may provide a habitat or shelter for F. koreansis and thereby function as a dispersal vector for this harmful epiphytic dinoflagellate.

     

The S phase is discrete and is controlled by the circadian clock in the marine dinoflagellate Gonyaulax polyedra

Cloned cultures of the dinoflagellate Gonyaulax polyedra grown in a 12-h light-12-h dark cycle (LD 12:12) were synchronized to the beginning of G₁ by a two sequential filtration technique. After the second filtration, with the cultures growing in LD 12:12, not many cells had divided after 1 day, but approximately half underwent cell division after 2 days. Flow cytometric measurements of the cells revealed that there is one unique S phase starting about 12 h prior to cell division and lasting for less than 4 h. A majority of cells in cultures synchronized in the same way but maintained in continuous light (LL) after filtration also divided synchronously after 2 days. Just as for the cultures in LD 12:12, those in LL have a similar discrete DNA synthesis phase prior to division. It is concluded that the circadian control of cell division acts before the S phase, giving rise to a discontinuous DNA synthesis phased by the circadian clock.     

Inhibition of cell proliferation by mechanical agitation involves transient cell cycle arrest at G1 phase in dinoflagellates

Summary.  Cell proliferation of dinoflagellates is negatively affected by mechanical agitation and red tides caused by members of the group have been correlated with periods of calm sea conditions. The mechanism involved in the mechanically transduced inhibition of cell proliferation is thought to involve the disruption of the cell division apparatus. In this study, we used highly synchronized cells and flow cytometry to study the effects of mechanical agitation on cell cycle progression. We observed that mechanical agitation induced transient cell cycle arrest at G₁ phase, in both the heterotrophic dinoflagellate Crypthecodinium cohnii and the photosynthetic dinoflagellate Heteroscapsa triquetra. Received March 12, 2002; accepted July 20, 2002; published online November 29, 2002     

CELL CYCLE AND CELL MORTALITY OF ALEXANDRIUM MINUTUM (DINOPHYCEAE) UNDER SMALL‐SCALE TURBULENCE CONDITIONS1

Decreased net population growth rates and cellular abundances have been observed in dinoflagellate species exposed to small‐scale turbulence. Here, we investigated whether these effects were caused by alterations in the cell cycle and/or by cell mortality and, in turn, whether these two mechanisms depended on the duration of exposure to turbulence. The study was conducted on the toxic dinoflagellate Alexandrium minutum Halim, with the same experimental design and setup used in previous studies to allow direct comparison among results. A combination of microscopy and Coulter Counter measurements allowed us to detect cell mortality, based on the biovolume of broken cells and thecae. The turbulence applied during the exponential growth phase caused an immediate transitory arrest in the G2/M phase, but significant mortality did not occur. This finding suggests that high intensities of small‐scale turbulence can alter the cell division, likely affecting the correct chromosome segregation during the dinomitosis. When shaking persisted for >4 d, mortality signals and presence of anomalously swollen cells appeared, hinting at the activation of mechanisms that induce programmed cell death. Our study suggests that the sensitivity of dinoflagellates to turbulence may drive these organisms to find the most favorable (calm) conditions to complete their division cycle.     

Physiological and Optical Responses of the Harmful Dinoflagellate Heterocapsa circularisquama to a Range of Salinity

The responses of division rate, cell volume, cellular carbon (C) and nitrogen (N), cellular pigments and optical characteristics to changes in salinity were examined in the dinoflagellate Heterocapsa circularisquama. The physiological and optical characteristics of H. circularisquama were significantly affected by changes in salinity. When cells were exposed to different salinities, they exhibited physiological acclimation by adjusting their cellular properties associated with growth. This could be a beneficial tactic for ensuring proliferation and limiting damages induced by adverse environmental factors. The results of this study could be essential for assisting in the development of growth models for H. circularisquama.     

Improvement in growth and toxin production of Alexandrium tamarense by two-step culture method

The growth and toxin content of the dinoflagellate Alexandrium tamarense ATHK was markedly affected by culture methods. In early growth phase at lower cell density static or mild agitation methods were beneficial to growth, but continuous agitation or aeration, to some extent, had an adverse effect on cell growth. Static culture in 2 L Erlenmeyer flasks had the highest growth rate (0.38 d⁻¹) but smaller cell size compared with other culture conditions. Cells grown under aerated conditions possessed low nitrogen and phosphorus cell yields, namely high N and P cell-quota. At day 18, cells grown in continuous agitated and 1 h aerated culture entered the late stationary phase and their cellular toxin contents were higher (0.67 and 0.54 pg cell⁻¹) compared with cells grown by other culture methods (0.27–0.49 pg cell⁻¹). The highest cell density and cellular toxin content were 17190 cells mL⁻¹ and 1.26 pg cell⁻¹ respectively in an airlift photobioreactor with two-step culture. The results indicate that A. tamarense could be grown successfully in airlift photobioreactor by a two-step culture method, which involved cultivating the cells statically for 4 days and then aerating the medium. This provides an efficient way to enhance cell and toxin yield of A. tamarense.     

Tracheary Element Formation from Single Isolated Cells in Culture

Friable callus tissue of Centaurea cyanus L. was grown on a solidified synthetic nutrient medium (EBM-1) to produce a tissue with a low frequency of differentiated tracheary elements. Tissues were then suspended in liquid nutrient medium with agitation to produce a suspension which was filtered and the single-cell suspension resulting was used as inoculum for either cell suspension cultures or for plating of cells into solidified medium in Petri plates. Media for the suspension cultures were selected to favor cytodifferentiation of tracheary elements. Differentiated tracheary elements formed as early as 10 days and numbers of tracheary elements increased with time roughly in relation to the increase in total cell number. From plating experiments it was shown conclusively that single isolated parenchyma cells differentiated directly into single isolated tracheary elements, although this event was rare. More usual was the division of isolated cells to form small colonies and then the differentiation of one, several or all of the cells into tracheary elements. Comparisons are made between results with cell plating experiments and cell suspension cultures. Optimism is expressed for finding a cell suspension culture system for studying cytodifferentiation.     

Morphological adaptation and inhibition of cell division during stationary phase in Caulobacter crescentus

During exponential growth, each cell cycle of the α-purple bacterium Caulobacter crescentus gives rise to two different cell types: a motile swarmer cell and a sessile stalked cell. When cultures of C. crescentus are grown for extended periods in complex (PYE) medium, cells undergo dramatic morphological changes and display increased resistance to stress. After cultures enter stationary phase, most cells are arrested at the predivisional stage. For the first 6–8 days after inoculation, the colony-forming units (cfu) steadily decrease from 10⁹ cfu ml⁻¹ to a minimum of 3 × 10⁷ cfu ml⁻¹ after which cells gradually adopt an elongated helical morphology. For days 9–12, the cfu of the culture increase and stabilize around 2 × 10⁸ cfu ml⁻¹. The viable cells have an elongated helical morphology with no constrictions and an average length of 20 μm, which is 15–20 times longer than exponentially growing cells. The level of the cell division initiation protein FtsZ decreases during the first week in stationary phase and remains at a low constant level consistent with the lack of cell division. When resuspended in fresh medium, the elongated cells return to normal size and morphology within 12 h. Cells that have returned from stationary phase proceed through the same developmental changes when they are again grown for an extended period and have not acquired a heritable growth advantage in stationary phase (GASP) compared with overnight cultures. We conclude that the changes observed in prolonged cultures are the result of entry into a new developmental pathway and are not due to mutation.     

Synchronization of encystment of <Emphasis Type="BoldItalic">Scrippsiella lachrymosa</Emphasis> (Dinophyta)

The encystment of Scrippsiella lachrymosa cells (strain B-10), which can be induced reliably in encystment medium, was inhibited by stirring the culture. 100 mL cultures in glass beakers were stirred at 1 rotation s⁻¹. Stirring inhibited vegetative cells from congregating (swarming) at the walls of the culture container. When stirring was stopped, a rapid induction of sexual reproduction was seen. As soon as stirring stopped (within 2 min), cells were observed swarming near the edges of the glass beaker. Four days after cessation of stirring, large percentages of the cells were mating and, after 7 days, most were zygotes. Cultures were observed after 31, 38, and, 45 days of stirring. When cultures were stirred for 45 days, cysts developed in the stirred treatments, but these cysts were attached to flocculent material that had also formed in the medium. The use of this laboratory method is advantageous for the study of the mating through cyst stages of the dinoflagellate life history. This method may also demonstrate the need for a ‘surface’ as a place for the dinoflagellate to congregate in order to successfully encyst and may help explain environmental observations of encystment at pycnoclines.     

A PHAGOTROPHICALLY DERIVABLE GROWTH FACTOR IN THE PLASTIDIC DINOFLAGELLATE GYRODINIUM RESPLENDENS (DINOPHYCEAE)

The marine dinoflagellate Gyrodinium resplendens Hulburt is a mixotroph. It possesses chloroplasts and is photosynthetic, and it also feeds phagotrophically on another dinoflagellate, Prorocentrum minimum (Pavillard) Schiller. The species could be cultivated only in food-replete cultures. When kept in cultures without food, cellular chl a content and photosynthetic activity of G. resplendens decreased and growth ceased after a few days. In food-replete cultures, G. resplendens could grow strictly heterotrophically in darkness, but growth rate was then three times lower than in food-replete cultures kept in light. It is suggested that the main importance of phagotrophy is to acquire a growth factor essential to photosynthetic growth. The addition of soil extract or amino acids to the growth medium induced enhanced photosynthetic growth of the species even without the presence of particulate food, but only for approximately 2 weeks. Long-term starvation of G. resplendens led to loss of the ability to feed, and therefore starved cells eventually reached a point of no return where neither photosynthesis nor phagotrophy could sustain further growth. Light microscopical observations on G. resplendens revealed new morphological and behavioral details of the species.     

RESPONSE OF MARINE SYNECHOCOCCUS (CYANOPHYCEAE) CULTURES TO IRON NUTRITION1

Three clones of marine Synechococcus (WH6501, WH7803, and WH8018) were grown through at least three transfers, at 6-day intervals, in synthetic medium with total iron concentrations from 10^?9 to 10^?6 M. After 6 days of exponential growth, these cultures were harvested, and the cell density and protein and pigment concentrations were measured. Aliquots of the culture were assayed for their carbon fixation rates at two light intensities. Cell density and protein concentration increased by up to 7.8 times over a range of iron from the lowest (10^?9 M) to the highest concentrations (10^?6 M). The concentration of chlorophyll-a and phycobiliproteins showed a wider range of response, increasing by up to 48 times. The carbon fixation rate (per mL of culture) also increased approximately 40 times over the total range of iron concentration. The ranges of these biochemical and physiological responses were much lower than the range of total available iron, which was 1000-fold, and the range of total cellular iron, which was estimated to be about 160-fold. This “less-than-linear” relationship indicates that the cells are adapting to make more efficient use of iron under limiting conditions. Our results demonstrate characteristics of iron-limited Synechococcus that may be important in understanding the relationships between primary productivity and iron availability in the oceans.     

Changes in Cell Size and DNA Content in Sulfolobus Cultures during Dilution and Temperature Shift Experiments

Stationary-phase cultures of different hyperthermophilic species of the archaeal genus Sulfolobus were diluted into fresh growth medium and analyzed by flow cytometry and phase-fluorescence microscopy. After dilution, cellular growth started rapidly but no nucleoid partition, cell division, or chromosome replication took place until the cells had been increasing in size for several hours. Initiation of chromosome replication required that the cells first go through partition and cell division, revealing a strong interdependence between these key cell cycle events. The time points at which nucleoid partition, division, and replication occurred after the dilution were used to estimate the relative lengths of the cell cycle periods. When exponentially growing cultures were diluted into fresh growth medium, there was an unexpected transient inhibition of growth and cell division, showing that the cultures did not maintain balanced growth. Furthermore, when cultures growing at 79 degrees C were shifted to room temperature or to ice-water baths, the cells were found to "freeze" in mid-growth. After a shift back to 79 degrees C, growth, replication, and division rapidly resumed and the mode and kinetics of the resumption differed depending upon the nature and length of the shifts. Dilution of stationary-phase cultures provides a simple protocol for the generation of partially synchronized populations that may be used to study cell cycle-specific events.     

Growth and toxin production in batch cultures of a marine dinoflagellate Alexandrium tamarense HK9301 isolated from the South China Sea

Nutritional and environmental conditions were characterized for a batch culture of the marine dinoflagellate Alexandrium tamarense HK9301 isolated from the South China Sea for its growth (cells ml⁻¹), cellular toxin content (Qt in fmol cell⁻¹) and toxin composition (mol%). Under a nutrient replete condition, Qt increased with cell growth and peaked at the late stationary phase. Toxin content increased with the nitrate concentration in the culture while it reached a maximum at 5 μM phosphate. When nitrate was replaced with ammonia, Qt decreased by 4.5-fold. Salinity and light intensity were important factors affecting Qt. The latter increased two-fold over the range of salinity from 15 to 30‰, while decreased 38% as light intensity increased from 80 to 220 μE m⁻² s⁻¹. Toxin composition varied with growth phase and culture conditions. In nutrient replete cultures, toxin composition varied greatly in the early growth phase (first 3 days) and then C1/C2, C3/C4 and GTX1 remained relatively constant while GTX4 increased from 32 to 46% and GTX5 decreased from 28 to 15%. In general, the composition of GTXs was affected in a much greater extent than C toxins by changes in nutrient conditions, salinity and light intensity. This is especially true with GTX4 and GTX5. These data indicate that the cellular toxin content and toxin composition of A. tamarense HK9301 are not constant, but that they vary with growth phase and culture conditions. Use of toxin composition to identify a toxigenic marine dinoflagellate is not always valid. The data also reveal that high salinity and low light intensity, together with high nitrate and low phosphate concentrations, would favor toxin production by this species.     

Adaptation to cycloheximide of macromolecular synthesis in Tetrahymena

Cycloheximide (CHI) at 10 ng/ml partially inhibited protein synthesis in exponential cultures of Tetrahymena Sp. At 20 ng/ml or greater, inhibition was complete. When protein synthesis was inhibited to any extent, cell division ceased immediately. In all instances where measured, synthesis of RNA and DNA also ceased. After a period of delay, cellular functions reinitiated in the order: (i) protein synthesis, (ii) DNA synthesis and, (iii) RNA synthesis and cell division. The delay in cell division was divided into three phases of: I, zero; II, low; and, III, fully recovered rates of exponential protein synthesis. The length of the three phases increased with increasing concentration of CHI Prior growth of cells for one generation in the presence of 7.5 ng/ml CHI (facilitation) eliminated phase I and slightly decreased phases II and III following subsequent challenge with an inhibitory concentration of CHI. Facilitation for six generations further decreased phases II and III. Protein synthesis and cell division were not inhibited during facilitation In the culture, succinate dehydrogenase activity did not increase during the delay but increased normally at the onset of division. In contrast, NADPH-cytochrome c reductase activity continued to increase for an hour after inhibition of protein synthesis, was constant for a period and did not increase again until an hour after reinitiatoin of cell division and RNA synthesis Inhibition of division of all cells was immediate and reinitiation of synthesis and cell division was non-synchronous.     

INGESTION AND RETENTION OF CHROOMONAS SPP. (CRYPTOPHYCEAE) BY GYMNODINIUM ACIDOTUM (DINOPHYCEAE)1

Gymnodinium acidotum Nygaard, a blue-green dinoflagellate previously shown to contain cryptophycean chloroplasts and other organelles, was observed from water and soil samples and in culture. The dinoflagellate excysts from soil samples as a mononucleated colorless cell that is positively phototactic. Colorless cells in unialgal culture remain colorless and can only be maintained less than one week whereas pigmented cells cultured unialgally grow for 10 days but then decline rapidly. Colorless cells cultured with Chroomonas spp. regain chloroplasts and have been maintained in mixed cultures for nine months. Fifty-seven percent of the dinoflagellates from mixed cultures are bi-nucleated, and three cells have been observed possibly ingesting cryptophytes. We suggest that cryptophycean chloroplasts are retained and possibly utilized by G. acidotum for at least ten days and then digested.     

The Role of Intercellular Contacts in the Initiation of Growth and in the Development of a Transiently Nonculturable State by Cultures of Rhodococcus rhodochrous Grown in Poor Media

It was found that the growth of Rhodococcus rhodochrous cells in a modified Saton’s medium strongly depends on the rate of culture agitation in the flask: agitation at 250 rpm in flasks with baffles stops cell multiplication, whereas slight agitation leads to pronounced culture growth. The growth retardation phenomenon was reversible and did not manifest itself in exponential-phase cultures or when the cells were grown in a rich medium; furthermore, it was not connected with the degree of culture aeration. When agitated at a moderate rate, the bacterial cells formed aggregates in the lag phase, which broke up into single cells in the exponential phase. The inhibitory effect of vigorous agitation was removed by the addition, to the medium, of the supernatant (SN) of a log-phase culture grown in the same medium with moderate agitation. Vigorous agitation is thought to interfere with cell contact, whose establishment is necessary for the development of an R. rhodochrous culture in a poor medium, which occurs in the form of (micro) cryptic growth. When grown in a modified Saton’s medium, R. rhodochrous cells were capable of transition, in the prolonged stationary phase, to a resting and transiently nonculturable state. Such cells could be resuscitated by incubation in a liquid medium with the addition of the supernatant or the Rpf secreted protein. The formation of transiently nonculturable cells was only possible under the conditions of a considerable agitation rate (250–300 rpm), which prevented secondary (cryptic) growth of the culture. This circumstance indicates the importance of intercellular contacts not only for the initiation of growth but also for the transition of the bacteria to a dormant state.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 489–797.Original Russian Text Copyright © 2005 by Voloshin, Shleeva, Syroeshkin, Kaprelyants.     

Growth inhibition of dinoflagellate algae in shake flasks: Not due to shear this time!

Large scale algae cultures present interesting challenges in that they exhibit characteristics of typical bacterial and animal cell cultures. One current commercial food additive, docosahexaenoic acid (DHA), is produced using the dinoflagellate algae, Crypthecodinium cohnii. Like animal cell culture, the perceived sensitivity of algae culture to hydrodynamic forces has potentially limited the agitation and aeration applied to these systems. However, the high density cultivation of C. cohnii required for an economically feasible process inevitably results in high oxygen demand. In this study, we demonstrated what first appeared to be a problem with shear sensitivity in shake flasks is most probably a mass transfer limitation. We subsequently demonstrated the limit of chronic and rapid energy dissipation rate, EDR, that C. cohnii cells can experience. This limit was determined using a microfluidic device connected in a recirculation loop to a stirred tank bioreactor, which has been previously used to repeatedly expose animal cells to high levels of EDR. Inhibition of cell growth was observed when C. cohnii cells were subjected to an EDR of 5.9 × 10⁶ W/m³ with an average frequency of 0.2/min or more. This level of EDR is sufficiently high that C. cohnii can withstand typically encountered hydrodynamic forces in bioprocesses. This result suggests that at least one dinoflagellate algae, C. cohnii, is quite robust with respect to hydrodynamic forces and the scale‐up of process using this type of algae should be more concerned with providing sufficient gas transfer given the relatively high oxygen demand. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010