Using cell cycle analysis to estimate in situ growth rate of the dinoflagellate Dinophysis acuminata:drawbacks of the DNA quantification method

Dinophysis acuminata is a mixotrophic dinoflagellate frequently causing diarrhetic shellfish poisoning. D. acuminata was isolated from Danish coastal waters and cultivated using the mixotrophic ciliate Mesodinium rubrum as prey. The roles of food uptake and photosynthesis for the growth and survival of D. acuminata were studied. The observed maximum growth rate was ca. 0.45 d -1 at an irradiance of 100 µmol photons m -2 s -1 when supplied with well-fed M. rubrum at concentrations >1000 M. rubrum ml . Apart from the importance of prey concentration, data revealed that ingestion and growth of D. acuminata are, to a certain degree, dependent on the growth rate of its ciliate prey. Photosynthesis was studied in a culture of D. acuminata, initially grown at prey saturation (>1000 M. rubrum cells ml -1) and subsequently allowed to deplete the prey. When the ciliate prey was added, the photosynthetic rate of D. acuminata increased from about 7 to 38 pg C cell -1 h -1 within the first 2 d. When subsequently subjected to starvation, the photosynthetic activity rapidly decreased to a pre-feeding level, and, without a minimum food uptake, D. acuminata was not able to maintain photosynthetic growth. At high prey concentrations, 70 to 90% of the gross C uptake can be explained by food uptake. However, at low prey concentrations, only 0 to 55% of the gross C uptake is likely to be derived from food uptake. The data indicate that in natural environments, D. acuminata may often be food limited, and, in this situation, photosynthesis may not only be a supplement to the basic nutrition, but rather the primary C source.KEY WORDS: Dinophysis acuminata · Dinoflagellate · Mixotrophy · Photosynthesis · Growth · Survival · Mesodinium rubrumResale or republication not permitted without written consent of the publisher

Section: Growth and Grazingsupporting

confidence: 76%

Role of food uptake for photosynthesis, growth and survival of the mixotrophic dinoflagellate Dinophysis acuminata

Riisgaard¹,

Hansen²

2009

“…There- ), was a discrete, rapid (2 h) process. In contrast, Gisselson et al (1999), who applied the same technique to populations of D. acuminata from the Gullmar Fjord (Skagerrak, Sweden), found a constantly high percentage (23 to 43%) of cells with a double content of DNA (G2 + M cells), very poor synchronisation, and lack of a clear cell-division pattern. These latter authors concluded that the microfluorimetric method applied to several hundreds of cells was inadequate to detect low degrees of synchronization, especially with regard to the S phase.…”

Section: Discussionmentioning

confidence: 99%

“…This phenomenon might explain the observations of Gisselson et al (1999): they applied the method of Carpenter & Chang (1988) to natural populations of Dinophysis acuminata after a sudden decrease in insolation, and found a constantly high percentage (23 to 43%) of cells with a 2q content of DNA and no synchronization. Our interpretation of the results of Gisselson et al (1999) is that they were dealing with a population stressed by changes in weather conditions, and by the late time of year in the dynamic waters of the Gullmarfjord that had a very low division rate and probably an accumulation of 2qDNA cells. Another case of poor synchronization was described by Carpenter et al (1995) in a D. norvegica population in the Baltic Sea thermocline under low light intensity.…”

Section: Cell Division Patterns In Natural Populations Ofmentioning

confidence: 95%

Cell cycle patterns and estimates of in situ division rates of dinoflagellates of the genus Dinophysis by a postmitotic index

Reguera¹,

Garcés²,

Pazos³

et al. 2003

A cell cycle-analysis method based on morphological recognition of cytokinesis and sulcal list regeneration was chosen to estimate in situ division rates (µ) of 4 dinoflagellate species of the genus Dinophysis, associated with diarrhetic shellfish poisoning (DSP), following 2 different models. Sampling over 24 h was conducted on 4 mini-cruises in the Galician rías during spring and autumn proliferations of these species. Frequencies of paired and recently divided cells in integrated water samples (0 to 20 m) were measured at 30, 60, or 120 min intervals. Cellular division was phased in D. acuminata, D. acuta, D. caudata and D. tripos, but the shape of the phase fraction curves and the values of estimated division rates varied considerably between seasons and cruises for the same species. Frequencies of paired plus recently divided cells were maximal at dawn in D. acuminata, and 2 to 3 h later in the other species. The results presented here confirm that the cytokinetic (paired) phase can be very fast in Dinophysis spp. (0.3 to 2.7 h), but sulcal list regeneration was shown to be a more stable process and an unambiguous marker of cellular division. This 'postmitotic index' allowed estimates of µ at low field concentrations (10 2 to 10 3 cell l -1 ) of the target species and required a short time for sample processing (1 to 2 h per sample). Moderate (0.24) to high (0.57) values of µ were found under oceanographic conditions considered unfavourable for growth of Dinophysis spp., and the phase in the population growth season seemed to be a key factor affecting this value. A critical revision of previous results of asynchronous division obtained in cell cycle studies of Dinophysis spp. is presented. It is suggested that monitoring the content of DNA per cell through the cell cycle in Dinophysis spp. is not a reliable method until a reasonable knowledge on the nuclear behaviour during sexual processes and other nonmitotic processes is available for these species, and that even accepting that mitosis is a non-return process, cell division may be arrested in one of its phases, adding further inconsistencies to µ measurements based on quantification of DNA per cell.

“…Using these microfluorometry techniques, t d can be estimated in populations where cell division is to some degree synchronized. This is accomplished by monitoring changes in the relative proportion of G 1 to S + G 2 + M phase cells through time and applying deconvolution techniques to establish the length of the terminal event (Whitely et al 1993, Gisselson 1999. In this study, the method employed was less sensitive and only capable of detecting M phase cells.…”

Section: Methodsmentioning

confidence: 99%

Effect of diel and interday variations in light on the cell division pattern and in situ growth rates of the bloom-forming dinoflagellate Heterocapsa triquetra

Litaker¹,

E.²,

Rhyne³

et al. 2002

Heterocapsa triquetra is an important bloom-forming dinoflagellate found in estuaries and nearshore regions worldwide. In an initial time-intensive study, the shallow, tidally mixed Newport River estuary, North Carolina, USA, was sampled from a fixed point located in the middle of the estuary every 2 h for 2 wk during the development of an H. triquetra bloom. The objective of this study was to investigate how short-term, high-frequency changes in temperature, light and salinity affected diel and interday cell division patterns and in situ growth rates of H. triquetra. During this study, phytoplankton samples were preserved in buffered formaldehyde and mitotic indices determined by acridine orange staining. The diel division pattern showed a nocturnal maximum between 23:00 and 05:00 h with reduced division during the day, a pattern characteristic of most dinoflagellates. The relative proportion of binucleate cells present during the day was influenced by interday variations in total irradiance, increasing during 2 of the 3 periods when there were 3 or more consecutive high light days (> 28 E m -2 d -1). Approximately 40% of the overall variation in interday division rates could be accounted for by differences in daily irradiance. The interday light differences were largely due to well-developed atmospheric frontal systems that brought increased cloud cover to the study area at regular 3 to 4 d intervals. The initial study, however, was of insufficient length to determine if the transient day-to-day light limitation could significantly affect seasonal bloom formation. A second longer-term, spatially intensive study was therefore undertaken to assess the relative importance of the incident light levels and nutrient inputs in controlling H. triquetra bloom initiation. During the second study, the estuary was monitored for photosynthetically active radiation (PAR), salinity, temperature, inorganic nutrients and cell densities of H. triquetra at 9 locations every wk from 23 December 1997 to 27 March 1998. Maximal H. triquetra bloom formation occurred during a 2 wk period when daily incident light levels were at or near the annual low. This suggested that H. triquetra is well adapted for utilizing low light levels and that variation in in situ growth rates in response to daily changes in PAR had little effect on bloom development. Instead, bloom initiation began with inputs of nitrogen-rich water following a runoff event, indicating that nutrient inputs are much more important in controlling bloom development than is light.