The use of the chemostat to study the relationship between cell growth rate, viability, and the effect of interferon on L 1210 cells

Mouse leukemia L 1210 cells were cultivated in the chemostat at growth rates ranging from 0.1 day⁻¹ (population doubling time (T_d) 166.3 h) to 2.0 day⁻¹ (T_d 8.3 h). At growth rates of 1.0 day⁻¹ and above, the viability of the steady-state culture was greater than 99%. However, below 1.0 day⁻¹ there was a progressive decrease in the viability of the culture with decreasing growth rate until a minimum growth rate (0.1 day⁻¹) was reached below which steady-state cultures of L 1210 cells could not be established. Interferon treatment had no effect on the viability (>99%) of L 1210 cells cultivated at fast growth rates in the chemostat, whereas at slow growth rates (0.35 day⁻¹) interferon treatment markedly reduced the viability of the culture, even though the percentage increase in the doubling time of interferon-treated cultures was the same for cells cultivated at both fast and slow growth rates. Thus, although interferon is not directly cytotoxic, it can cause cell death by reducing the rate of cell multiplication below the minimum value compatible with viability.     

ACTIVE GROWTH OF THE OCEANIC DINOFLAGELLATE CERATIUM TERES IN THE CARIBBEAN AND SARGASSO SEAS ESTIMATED BY CELL CYCLE ANALYSIS1

The growth rate of an oceanic dinoflagellate, Ceratium teres Kofoid, was investigated in the Sargasso and Caribbean Seas from September 1989 to July 1990 using the cell cycle analysis method. Estimated growth rates ranged from 0.29 to 0.58 day^?1 and were 1.5–7.2 times higher than generally accepted rates for oceanic dinoflagellates. The higher rates in this report were mainly due to an improvement in techniques that determine the duration of a terminal cell cycle phase in situ. The day-to-day variation in growth rates was surprisingly small, but, from long-term measurements, a weak correlation was found among temperature, daily irradiance, and seasonal growth rate. The calculated species-specific primary production ranged from 0.5 to 1.8 mg C·m^?2·day^?1, about 1% of the estimated total production. Ceratium teres may be an important carbon source at the base of the grazing food chain.     

Dinophysis blooms in the deep euphotic zone of the Baltic Sea: do they grow in the dark?

In situ growth rates of the toxin-producing dinoflagellate Dinophysis norvegica collected in the central Baltic Sea were estimated during the summers of 1998 and 1999. Flow cytometric measurements of the DNA cell cycle of D. norvegica yielded specific growth rates (μ) ranging between 0.1 and 0.4 per day, with the highest growth rates in stratified populations situated at 15–20 m depth. Carbon uptake rates, measured using ¹⁴C incubations followed by single-cell isolation, at irradiances corresponding to depths of maximum cell abundance were sufficient to sustain growth rates of 0.1–0.2 per day. The reason for D. norvegica accumulation in the thermocline, commonly at 15–20 m depth, is thus enigmatic. Comparison of depth distributions of cells with nutrient profiles suggests that one reason could be to sequester nutrients. Measurements of single-cell nutrient status of D. norvegica, using nuclear microanalysis, revealed severe deficiency of both nitrogen and phosphorus as compared to the Redfield ratio.It is also possible that suitable prey or substrate for mixotrophic feeding is accumulating in the thermocline. The fraction of cells containing digestive vacuoles ranged from 2 to 22% in the studied populations. Infection by the parasitic dinoflagellate Amoebophrya sp. was observed in D. norvegica in all samples analysed. The frequency of infected cells ranged from 1 to 3% of the population as diel averages, ranging from 0.2 to 6% between individual samples. No temporal trends in infection frequency were detected. Estimated loss rates based on observed infection frequencies were 0.5–2% of the D. norvegica population daily, suggesting that these parasites were not a major loss factor for D. norvegica during the periods of study.     

CHEMICAL ESTIMATIONS OF DNA CHANGES DURING SYNCHRONOUS GROWTH OF EUDORINA ELEGANS (CHLOROPHYCEAE)12

Analysis of synchronous populations of Eudorina elegans Ehrenberg reveals that DNA replication occurs coincidentally with the very rapid sequence of cell divisions. The average doubling time for DNA in such synchronous populations is 40 min. The basal amount of DNA/E. elegans cell is estimated to be 0.5 × 10^?12 g.     

Characteristics of the chemostat culture of murine leukemia L 1210 cells

Mouse leukemia L 1210 cells were cultivated under glucose limitation in a chemostat. More than 20 steady-states were established over 9 different dilution rates ranging from 0.20 day⁻¹ (cell doubling time 83 h) to 2.0 days⁻¹ (cell doubling time 8.3 h). The steady-states were characterized by: a constant cell number, constant cell volume, constant concentrations of DNA, RNA, and L-lactate (in the culture supernatant), a constant percentage of cells labelled by autoradiography, and constant rate of incorporation of [³H]TdR, [³H]uridine, and ¹⁴C-labelled amino acids into cellular acid-precipitable material. Individual steady-states were maintained for periods up to 600 h continuous operation of the chemostat. A maximum output of 66.4 × 10⁶ cells/h was obtained at a dilution rate of 1.3 day⁻¹. The glucose substrate constant was determined as 0.0063 mg/ml. The relationships between dilution rate and the steady-state cell concentration, glucose concentration, and output of L 1210 cells from the chemostat, were in general agreement with the theoretical curves. It was found that the principles of continuous culture derived from the study of microorganisms are to a large extent applicable to the cultivation of animal cells.     

Bottom-up and top-down controls of the microbial food web in the Southern Ocean: experiments with manipulated microcosms

Summary We have studied bottom-up and top-down control of the Southern Ocean microbial food web by microcosm experiments. Water from the Weddell Sea and Weddell Scotia Confluence were used for the experiments. Microcosms were manipulated by nutrients and light, and by size-selective screening. Incubation at the higher light level doubled phytoplankton growth rates from 0.12 to 0.24 day^–1 in the Weddell experiment and from 0.15 to 0.30 day^–1 in the Confluence experiment. Nutrient enrichment had no significant effect on growth rates in either of the experiments, indicating that phytoplankton growth was not nutrient-limited. In the microcosms where dinoflagellate growth rate was different, high dinoflagellate numbers were reflected as depressed nanoflagellate growth as well as depressed growth of phytoplankton, suggesting that dinoflagellates controlled both heterotrophic nanoflagellates and autotrophic nanoplankton. Only during short periods, when dinoflagellate numbers were low, could exponential growth of nanoflagellates be demonstrated. Bacterioplankton growth rates were, on average, 0.26 day^–1 in the Weddell experiment and 0.22 day^–1 in the Confluence experiment. Bacteria were controlled by heterotrophic nanoflagellates. Potential growth rates up to 0.75 day^–1 were measured from batch cultures without predators. With the microcosm experiments, we could demonstrate a strong top-down control by dinoflagellates on phytoplankton and on heterotrophic nanoflagellates, and a control by heterotrophic nanoflagellates on bacteria. We could also demonstrate weak nutrient limitation on autotrophs and substrate limitation on heterotrophic bacteria. In the two study areas, biomass production and carbon flow were mediated mainly by organisms that passed through a 20 m net and had growth rates in the order of 0.20 to 0.30 day^–1.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Competitive and Cooperative Interactions Affecting a Fermentative Spirochete in Anaerobic Chemostats

Terminal restriction fragment length polymorphism and fluorescent in situ hybridization revealed that spirochete-related populations dominated two glucose-fed methanogenic bioreactor communities at dilution rates of 0.06, 0.13, and 0.17 day^–1. At dilution rates of 0.25 and 0.50 day^–1, spirochete-related populations decreased while Clostridium-related populations increased. Isolates representing both dominant populations were obtained (Treponema R8 and Clostridium S9) and competed against each other in continuous culture. Treponema R8 outcompeted Clostridium S9 at all dilution rates applied (0.17 to 1.0 day^–1) when sufficient pantothenate was supplied in the medium. Without sufficient pantothenate, the population size of Treponema R8 was limited to 40% of the total cells. Coculture of Treponema R8 with Methanobacterium bryantii increased the cell yield of Treponema R8 and relieved the pantothenate requirement. Triculture of Treponema R8, Clostridium S9, and M. bryantii in pantothenate-deficient medium allowed Treponema R8 to outcompete Clostridium S9 in continuous culture up to a dilution rate of 0.50 day^–1. These experiments demonstrate that cofactor and vitamin requirements can affect the competitive success of a microbial species. Present affiliation: S.L. Dollhopf Department of Biology, Florida State University, Tallahassee, FL 32303, USA     

Phytoplankton growth rates in the Ross Sea, Antarctica, determined by independent methods: temporal variations

The development of the seasonal phytoplankton bloom in the Ross Sea was studied during two cruises. The first, conducted in November-December 1994, investigated the initiation and rapid growth of the bloom, whereas the second (December 1995-January 1996) concentrated on the bloom's maximum biomass period and the subsequent decline in biomass. Central to the understanding of the controls of growth and the summer decline of the bloom is a quantitative assessment of the growth rate of phytoplankton. Growth rates were estimated over two time scales with different methods. The first estimated daily growth rates from isotropic incorporation under simulated in situ conditions, including ¹⁴C, ¹⁵N and ³²Si uptake measurements combined with estimates of standing stocks of particulate organic carbon, nitrogen and biogenic silica. The second method used daily to weekly changes in biomass at selected locations, with net growth rates being estimated from changes in standing stocks of phytoplankton. In addition, growth rates were estimated in large-volume experiments under optimal irradiances. Growth rates showed distinct temporal patterns. Early in the growing season, short-term estimates suggested that growth rates of in situ assemblages were less than maximum (relative to the temperature-limited maximum) and were likely reduced due to low irradiance regimes encountered under the ice. Growth rates increased thereafter and appeared to reach their maximum as biomass approached the seasonal peak, but decreased markedly in late December. Differences between the major taxonomic groups present were also noted, especially from the isotopic tracer experiments. The haplophyte Phaeocystic antarctica was dominant in 1994 throughout the growing season, and it exhibited the greatest growth rates (mean 0.41 day^-1) during spring. Diatom standing stocks were low early in the growing season, and growth rates averaged 0.100 day^-1. In summer diatoms were more abundant, but their growth rates remained much lower (mean of 0.08 day^-1) than the potential maximum. Understanding growth rate controls is essential to the development of predictive models of the carbon cycle and food webs in Antarctic waters.      

AUTOLYSIS KINETICS OF THE MARINE DIATOM DITYLUM BRIGHTWELLII (BACILLARIOPHYCEAE) UNDER NITROGEN AND PHOSPHORUS LIMITATION AND STARVATION1

Autolysis kinetics in axenic cultures of the diatom Ditylum brightwellii (West) Grunow were studied under nutrient limitation in continuous cultures and under nutrient starvation in batch-mode cultures obtained by switching off nutrient supply in the continuous cultures. Under N limitation, the specific algal autolysis rates (δ, day^?1) were found constant at 0.014 ± 0.002 day^?1over a broad range of specific dilution rates (D, day^?1) (0.09–0.56 day^?1), implying an intrinsic death factor independent of the physiologzc state of the algal cells. Under P limitation, 8 was inversely related to D and ranged between 0.067 and 0.005 day^?1 at D = 0.17–0.44 day^?1. Under conditions of nutrient stamation, the degree of algal nutrient deficiency prior to stamation affected autolysis rates (δ_b, day^?1) and subsequently survival of the algal cultures. Nitrogen-starved D. brightwellii showed highest δ_b (maximum, 0.10 day^?1) when precultured at the higher growth rates. Phosphorus stamation led to highest δ_b (maximum, 0.21 day^?1) in the cultures preconditioned at the lower steady state growth rates. The lower death rates for D. brightwellii under limitation and starvation of N compared to P suggest that D. brightwellii was better equipped to handle N than P deficiency. The present results showed that cell lysis induced by nutrient stress was a significant cause of mortality in D. brightwellii and provided more insight into the field distribution of this neritic diatom.     

Effects of organic matter and season on leaf litter colonisation and breakdown in cave streams

1. Low organic matter availability is thought to be a primary factor influencing evolutionary and ecological processes in cave ecosystems. We examined links among organic matter abundance, macroinvertebrate community structure and breakdown rates of red maple (Acer rubrum) and corn litter (Zea mays) in coarse‐ (10 × 8 mm) and fine‐mesh (500‐μm) litter bags over two seasonal periods in four cave streams in the south‐eastern U.S.A. 2. Organic matter abundance differed among cave streams, averaging from near zero to 850 g ash‐free dry mass m^?2. Each cave system harboured a different macroinvertebrate community. However, trophic structure was similar among caves, with low shredder biomass (2–17% of total biomass). 3. Corn litter breakdown rates (mean k = 0.005 day^?1) were faster than red maple (mean k = 0.003 day^?1). Breakdown rates in coarse‐mesh bags (k = 0.001–0.012 day^?1) were up to three times faster than in fine‐mesh bags (k = 0.001–0.004 day^?1). Neither invertebrate biomass in litter bags nor breakdown rates were correlated with the ambient abundance of organic matter. Litter breakdown rates showed no significant temporal variation. Epigean (surface‐adapted) invertebrates dominated biomass in litter bags, suggesting that their effects on cave ecosystem processes may be greater than hypogean (cave‐adapted) taxa, the traditional focus of cave studies. 4. The functional diversity of our cave communities and litter breakdown rates are comparable to those found in previous litter breakdown studies in cave streams, suggesting that the factors that control organic matter processing (e.g. trophic structure of communities) may be broadly similar across geographically diverse areas.     

Survival and photosynthetic activity of different Dinophysis acuminata populations in the northern Baltic Sea

This study deals with a recently found phenomenon in the northern Baltic Sea: the occurrence of the dinoflagellate Dinophysis acuminata in the deep water below the thermocline. This was first observed in July 2001 at the station BY 15 in the Gotland Deep, where a sharp and intensive chlorophyll fluorescence signal was encountered at 77 m depth. The fluorescence peak was due to a dinoflagellate community dominated by Dinophysis acuminata (approximately 18 000 cells l⁻¹). The survival of this community was followed in laboratory incubations in low light (20 μE m⁻² s⁻¹) and low temperature (+5 °C). After 5 weeks incubation, 67–84% of the initial cell abundance was lost, while few D. acuminata cells survived up to 24 weeks in the original sample. During the incubation, the fluorescence signal of the cells became fainter and the chloroplasts smaller and aggregated. On two occasions a D. acuminata cell was found attached to a smaller cell by a thin cytoplasm strand, possibly indicating mixotrophic behavior. During the following summer (2002), the photosynthetic efficiency of D. acuminata collected from thermocline layers of few stations and from the nitracline (75–80 m) at one station was studied in photosynthesis irradiance (P–E) incubations. Photosynthetic activity occurred in all populations, with differences in their photosynthetic carbon uptake rates. Photosynthesis of D. acuminata populations was saturated between 250 and 500 μE m⁻² s⁻¹; maximum cell-specific carbon uptake rates (P_m) ranged from 160–925 pg C cell⁻¹ h⁻¹. The P_m-rates in populations originating below the thermocline and in an artificially darkened population were markedly lower than in populations from upper water layers. The varying maximum photosynthetic rates of these populations may reflect their history, e.g. time spent in different light environments.     

Diversity in the influence of temperature on the growth rates of freshwater algae, and its ecological relevance

1. Growth rates of seven species of planktonic algae were determined in culture over a range of temperature from 2 to 35 °C. Additional observations on growth and viability were made for 13 species in the temperature range 20–35 °C. 2. There was a wide range of growth rates between species at their optimal temperatures, from 1.7 divisions day^?1 (Asterionella formosa) to 0.3 divisions day^?1 (Ceratium furcoides). 3. There were considerable differences between species for growth at low and high temperature. Certain algae, including the diatom A. formosa and the flagellates Cryptomonas marssonii, Dinobryon divergens and Eudorina unicocca var. unicocca, had growth rates of 0.4 divisions day^?1 or more at 5 °C. The cyanophyte Tychonema (formerly Oscillatoria) bourrellyi, the xanthophyte Tribonema sp., the desmid Staurastrum cingulum and the large dinoflagellate C. furcoides grew poorly or not at all at this temperature. All 21 species tested could grow at 25 °C, but many – including most of the diatoms, some cyanophytes, and all the flagellates – failed to grow persistently at 30 °C. Only Aphanizomenon flos‐aquae survived with moderate increase at 35 °C, a lethal temperature for the other species. 4. The applicability was considered of proposed quantitative formulations of the rate‐temperature relationship. Simple exponential relationships applied only to very limited lower ranges of temperature. The relationship proposed by B?lehrádek was a better fit over a wider temperature range, but still excluded rate‐decline at high temperature. 5. The interspecific differences found are of potential significance for restrictions in natural distributions associated with season, altitude (especially above 500 m) and latitude.     

THE NUCLEAR CELL CYCLE IN CHLAMYDOMONAS (CHLOROPHYCEAE)1

The timing of replication and division of the Chlamydomonas Ehrenberg nucleus in the vegetative cell cycle and at gametogenesis was examined, using fluorescence microspectrophotometry with two fluorochromes, mithramycin and 4′,6-diamidino-2-phenylindole (DAPI). Under appropriate conditions, these bind specifically to DNA, and the fluorescence of the DNA fluorochrome complex is a quantitative measure of the DNA content. The alga is a haplont, which produces 2ⁿ daughter cells at the time of vegetative reproduction; cytokinesis and daughter cell release lag behind karyokinesis. No nucleus was found to contain more than the 2c quantity of DNA. Hence daughter cell production proceeds by doubling of the nuclear DNA followed by karyokinesis, in a repetitive sequence. As reported previously for C. reinhardtii Dangeard, the gametes of C. moewusii Gerloff contain the 1c amount of nuclear DNA. Several conflicting interpretations of the cell cycle sequence proposed in the literature were resolved.     

Mathematical Determination of Cell Population Doubling Times for Multiple Cell Lines

Cell cycle times are vital parameters in cancer research, and short cell cycle times are often related to poor survival of cancer patients. A method for experimental estimation of cell cycle times, or doubling times of cultured cancer cell populations, based on addition of paclitaxel (an inhibitor of cell division) has been proposed in literature. We use a mathematical model to investigate relationships between essential parameters of the cell division cycle following inhibition of cell division. The reduction in the number of cells engaged in DNA replication reaches a plateau as the concentration of paclitaxel is increased; this can be determined experimentally. From our model we have derived a plateau log reduction formula for proliferating cells and established that there are linear relationships between the plateau log reduction values and the reciprocal of doubling times (i.e. growth rates of the populations). We have therefore provided theoretical justification of an important experimental technique to determine cell doubling times. Furthermore, we have applied Monte Carlo experiments to justify the suggested linear relationships used to estimate doubling time from 5-day cell culture assays. We show that our results are applicable to cancer cell populations with cell loss present.     

Kinetics of intracellular carbon allocation in a marine diatom

To test models of intracellular carbon flow we measured the labelling kinetics (from ¹⁴CO₂) of major classes of cell polymers (carbohydrate, protein, lipid) and of dissolved organic carbon produced by the marine diatom Thalassiosira pseudonana Hustedt, grown at rates of 0.2 to 2.0·day^?1 under nitrogen or light limitation. Compartmental analysis indicated that tracer carbon quickly entered respiratory and excretory streams, accumulating in the cells at the rate of net production after only 25–50% of cell generation (doubling) time. Respiration rates were low (≤ 0.1 · day^?1) and suggested that illuminated cells in steady-state growth made only minor use of oxidative respiration to support cell synthesis. The tracer was quick to enter all polymers; compartmental analysis indicated that polymer labelling rates were close to the rates of mass synthesis after several hours of incubation with ¹⁴C. Polymer labelling also showed a reallocation of photosynthate from protein to carbohydrate within a few hours of perturbation (shift-down) of nutrient supply in a N-limited chemostat. In steady-state growth, the protein: carbohydrate ratio increased directly with N-limited growth rate but attained its maximum under extreme light-limitation. Carbon flow into the metabolic processes of respiration, excretion and polymer synthesis appeared to be mediated by a small and rapidly cycled pool of substrates under all steady-state growth conditions.     

ENVIRONMENTAL FACTORS CONTROLLING ALEXANDRIUM TAMARENSE (DINOPHYCEAE) GROWTH RATE DURING A RED TIDE EVENT IN THE ST. LAWRENCE ESTUARY (CANADA)1

The dinoflagellate Alexandrium tamarense (Lebour) Balech 1985 is responsible for recurrent outbreaks of paralytic shellfish poisoning in the St. Lawrence Estuary. In July 1998, an A. tamarense red tide developed in the estuary with maximum cell concentrations reaching 2.3 × 10⁶ cells·L^?1 in brackish surface waters. To estimate the growth rate of these cells, surface water samples from different locations and days during the bloom were incubated for 5 to 9 days under in situ temperature and light conditions. Growth rates varied both spatially and temporally between 0 and 0.55 day^?1, reaching the maximum growth rate reported for this species in culture. High growth rates were measured even during the peak of the red tide, suggesting that the extremely high cell concentrations observed did not solely result from aggregation or physical concentration but also involved active cellular growth. Alexandrium tamarense cells were found over a large range of salinity (20.8–29.5 psu), but high densities and significant growth were only measured when salinity was lower than 24.5 psu. Under these conditions, the number of divisions achieved by A. tamarense was proportional to the amount of nitrate available at the beginning of the incubations, whereas variations in growth rate were apparently controlled by the availability of phosphate. We hypothesize that the ability of A. tamarense to perform vertical migrations and acquire nitrate at night pushes this species toward phosphate limitation in the St. Lawrence Estuary.     

In situ growth rate and distribution of the ichthyotoxic dinoflagellate Gyrodinium corsicum Paulmier in an estuarine embayment (Alfacs Bay, NW Mediterranean Sea)

Gyrodinium corsicum Paulmier produced massive blooms in Alfacs Bay (Ebro Delta, NW Mediterranean Sea) from December 1994 to April 1995, a period characterized by an initial period of water stability and low outward flux of water during subsequent months. The highest cell densities of G.corsicum were found at the bottom of the bay during the population maintenance period (from January to March). During the day, no differences in the vertical distribution of G.corsicum were observed and no diel in situ vertical migration of the population was recorded. The in situ growth rate of G.corsicum was estimated using the cell cycle method since the cell division cycle was well phased with the daily light cycle. The S phase fraction of G.corsicum reached a maximum near the middle of the dark period. The G2M peak usually occurred in the dark period. The duration of the S phase was 2.1-8.7 h and the duration of the G2M phase was 2.6-7.7 h. The estimated specific in situ growth rate of G.corsicum ranged from 0.94 day^-1 during the initial phases of the bloom to 0.3 day^-1 when the bloom was well developed. Growth rates, measured in different locations at the same time, varied by a factor of 1.5, suggesting that different parts of the same blooming population were at different stages of growth. The persistence of the G.corsicum bloom with high cell densities (10⁵-10⁶ cells l^-1) at the bottom of the bay is discussed in relation to the low cell losses by physical dispersion in this area and the lack of upward vertical migration of G.corsicum.      

How<Emphasis Type="Italic"> Daphnia</Emphasis> copes with excess carbon in its food

Animals that maintain near homeostatic elemental ratios may get rid of excess ingested elements from their food in different ways. C regulation was studied in juveniles of Daphnia magna feeding on two Selenastrum capricornutum cultures contrasting in P content (400 and 80 C:P atomic ratios). Both cultures were labelled with ¹⁴C in order to measure Daphnia ingestion and assimilation rates. No significant difference in ingestion rates was observed between P-low and P-rich food, whereas the net assimilation of ¹⁴C was higher in the treatment with P-rich algae. Some Daphnia were also homogeneously labelled over 5 days on radioactive algae to estimate respiration rates and excretion rates of dissolved organic C (DOC). The respiration rate for Daphnia fed with high C:P algae (38.7% of body C day^-1) was significantly higher than for those feeding on low C:P algae (25.3% of body C day^-1). The DOC excretion rate was also higher when animals were fed on P-low algae (13.4% of body C day^-1) than on P-rich algae (5.7% of body C day^-1) . When corrected for respiratory losses, total assimilation of C did not differ significantly between treatments (around 60% of body C day^-1). Judging from these experiments, D. magna can maintain its stoichiometric balance when feeding on unbalanced diets (high C:P) primarily by disposing of excess dietary C via respiration and excretion of DOC.     

LOW THERMAL LIMIT OF GROWTH RATE OF SYMBIODINIUM CALIFORNIUM (DINOPHYTA) IN CULTURE MAY RESTRICT THE SYMBIONT TO SOUTHERN POPULATIONS OF ITS HOST ANEMONES (ANTHOPLEURA SPP.; ANTHOZOA,CNIDARIA)1

Symbiodinium californium (#383, Banaszak et al. 1993 ) is one of two known dinoflagellate symbionts of the intertidal sea anemones Anthopleura elegantissima, A. xanthogrammica, and A. sola and occurs only in hosts at southern latitudes of the North Pacific. To investigate if temperature restricts the latitudinal distribution of S. californium, growth and photosynthesis at a range of temperatures (5°C–30°C) were determined for cultured symbionts. Mean specific growth rates were the highest between 15°C and 28°C (μ 0.21–0.26 · d^?1) and extremely low at 5, 10, and 30°C (0.02–0.03 · d^?1). Average doubling times ranged from 2.7 d (20°C) to 33 d (5, 10, and 30°C). Cells cultured at 10°C had the greatest cell volume (821 μm³) and the highest percentage of motile cells (64.5%). Growth and photosynthesis were uncoupled; light‐saturated maximum photosynthesis (P_max) increased from 2.9 pg C · cell^?1 · h^?1 at 20°C to 13.2 pg C · cell^?1 · h^?1 at 30°C, a 4.5‐fold increase. Less than 11% of daily photosynthetically fixed carbon was utilized for growth at 5, 10, and 30°C, indicating the potential for high carbon translocation at these temperatures. Low temperature effects on growth rate, and not on photosynthesis and cell morphology, may restrict the distribution of S. californium to southern populations of its host anemones.