EFFECTS OF TEMPERATURE ON GROWTH,LIGHT ABSORPTION,AND QUANTUM YIELD IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

The effects of growth temperature on the marine chlorophyte Dunaliella tertiolecta Butcher were studied to provide a more mechanistic understanding of the role of environmental factors in regulating bio-optical properties of phytoplankton. Specific attention was focused on quantities that are relevant for modeling of growth and photosynthesis. Characteristics including chlorophyll a (chl z)-specific light absorption (a*_ph(λ)), C:chl a ratio, and quantum yield for growth (φ_μ) varied as functions of temperature under conditions of excess light and nutrients. As temperature increased over the range examined (12°-28°C), intracellular concentrations of chl a increased by a factor of 2 and a*_ph(λ) values decreased by more than 50% at blue to green wavelengths. The lower values of a*_ph(λ) were due to both a decrease in the abundance of accessory pigments relative to chl a and an increase in pigment package effects arising from higher intracellular pigment concentrations. Intracellular pigment concentration increased as a consequence of higher cellular pigment quotas combined with lower cell volume. At high growth temperatures, slightly more light was absorbed on a per-cell-C basis, but the dramatic increases in growth rate from μ= 0.5 d^?1 at 12° C to μ= 2.2 d^?1 at 28°C were primarily due to an increase in φ_μ (0.015–0.041 mol C (mol quanta)^?1). By comparison with previous work on this species, we conclude the effects of temperature on a*_ph(λ) and φ_μ are comparable to those observed for light and nutrient limitation. Patterns of variability in a*_ph(λ)and φ_μ as a function of growth rate at different temperatures are similar to those previously documented for this species grown at the same irradiance but under a range of nitrogen-limited conditions. These results are discussed in the context of implications for bio-optical modeling of aquatic primary production by phytoplankton.     

NITROGEN LIMITATION IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE) LEADS TO INCREASED SUSCEPTIBILITY TO DAMAGE BY ULTRAVIOLET‐B RADIATION BUT ALSO INCREASED REPAIR CAPACITY1

Chl fluorescence was used to measure the photosynthetic capacity of the green alga Dunaliella tertiolecta in order to investigate interactions between susceptibility to acute UV‐B radiation (UVBR, 280–320 nm) exposure and decreased nitrogen availability. Under UVBR exposure the decline in the fluorescence parameters F_v/F_m (the maximum effective quantum yield Φ_PSIIe‐max) and F_v′/F_m′ (the operational quantum yield of PSII, Φ_PSIIe) were enhanced with higher UVBR fluxes, with the data well described by the Kok model, inferring that a dynamic balance existed between damage and repair with the repair proportional to the pool size of inactivated targets. When UVBR exposure was coupled with nitrogen limitation, the inhibition of photosynthesis was intensified. Under the more severely N‐limited conditions, the damage rate increased. Unexpectedly, repair rates were also stimulated under N‐limited conditions, although this was insufficient to counteract the increase in damage, so the overall effect of N limitation was an enhancement of UVBR‐induced inhibition of photosynthesis.     

INTERACTIONS AMONG PHOSPHATE UPTAKE,PHOTOSYNTHESIS, AND CHLOROPHYLL FLUORESCENCE IN NUTRIENT‐LIMITED CULTURES OF THE CHLOROPHYTE MICROALGA DUNALIELLA TERTIOLECTA1

Phosphate‐limited and phosphate‐sufficient continuous cultures of the marine chlorophyte microalga Dunaliella tertiolecta Butcher were examined for their responses to the addition of phosphate. Phosphate‐limited cultures showed a marked quenching of chl fluorescence following a pulse of phosphate. This response was absent from cells growing under phosphate‐sufficient conditions. Both the extent of fluorescence quenching (where present) and the initial rate of change in quenching were dependent on the concentration of phosphate added to cell suspensions and on the degree of limitation (growth rate in continuous culture). The addition of phosphate also brought about a transient decrease in photosynthetic oxygen evolution and a stimulation in respiration, which were relaxed as the added phosphate was depleted from the external medium. The applicability of using nutrient‐induced fluorescence transients as a tool to identify the nutrient status of phytoplankton populations is discussed.     

AMMONIUM INDUCED PHOTOSYNTHETIC SUPPRESSION IN AMMONIUM LIMITED DUNALIELLA TERTIOLECTA (CHLOROPHYTA)1

Dunaliella tertiolecta (Butcher) was grown in chemostat culture over a wide range of ammonium limited growth rates. The addition of ammonium caused a rapid temporary suppression of photosynthetic carbon fixation. The magnitude of ammonium induced photosynthetic suppression increased with the severity of ammonium limitation. Cells growing at rates greater than ca. 80%μ_max exhibited no photosynthetic suppression in response to additions of the limiting nutrient. The duration of photosynthetic suppression was related to the concentration of added ammonium. Immediately following the suppression, photosynthesis was enhanced with respect to the controls. The eventual degree of enhancement increased with the concentration of added ammonium. Steady-state cellular chlorophyll concentrations, photosynthetic rates, and assimilation numbers are reported.     

ASSESSING PHYSIOLOGICAL STRESS IN THALASSIOSIRA FLUVIATILIS (BACILLARIOPHYTA) AND DUNALIELLA TERTIOLECTA (CHLOROPHYTA) WITH DCMU-ENHANCED FLUORESCENCE1

Exponentially growing cultures of Thalassiosira fluviatilis Hustedt and Dunaliella tertiolecta Butcher were exposed to 4 min temperature shocks of 5° to 20°C above ambient (20°C). Photosynthetic carbon fixation, changes in in vivo fluorescence and fluorescence on the addition of the herbicide DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) were measured over the subsequent 24 h. The fluorescence ratio (R, DCMU-enhanced fluorescence/in vivo fluorescence) paralleled changes in photosynthesis over this period; both were significantly reduced (P < 0.05) by temperature shocks of +15° and +20° C, but +5° and +10° C treatments had no inhibitory effect on either relative to the control. The instantaneous response obtained with the fluorescence ratio indicates that the technique might be applicable to routine bioassay procedures and thus replace the time consuming methods now used for the estimation of ¹⁴C-incorporation and growth rates.     

PHOTORESPIRATION IN CONTINUOUS CULTURE OF DUNALIELLA TERTIOLECTA (CHLOROPHYTA): RELATIONSHIPS BETWEEN SERINE, GLYCINE, AND EXTRACELLULAR GLYCOLATE

The concentrations of extracellular glycolate and intracellular free pools of serine and glycine were monitored in nitrogen-limited continuous cultures of Dunaliella tertiolecta (Butcher) UTEX LB999, grown at two different irradiances on a light:dark cycle. Under steady-state conditions, this microalga excreted into the medium a large amount of glycolate during the light phase, up to 100 nmol·(10⁶ cells)⁻¹ for a cell concentration of around 1.5 10⁸ cells·L⁻¹, but glycolate disappeared from the dissolved phase in the dark. Cells grown at 70 and those grown at 430 μmol photons·m⁻²·s⁻¹ differed in maximal glycolate concentration, intracellular serine and glycine concentrations, and serine:glycine ratio. Reversal of these photon flux densities to which the cultures were exposed caused rapid modification of the extracellular glycolate and intracellular serine and glycine pools. These results suggest that photorespiratory metabolism in D. tertiolecta could be approximately quantified by measuring the changes in dissolved glycolate and intracellular serine and glycine concentrations, extending previous results from cultured phytoplankton and suggesting methods for field studies.     

A SALT-INDUCED CHLOROPLAST PROTEIN IN DUNALIELLA SALINA (CHLOROPHYTA)1

The unicellular green alga Dunaliella salina Teod, is halophilic and wall-less. The cell acclimates to osmotic stresses by accumulation or degradation of glycerol. To investigate other mechanisms involved in its physiological recovery following hyperosmotic shocks, protein profiles from cells grown in various salinities were compared. A 13-kDa protein (P13) accumulated when cells were subjected to drastic hyperosmotic shock. Front our results with antibiotic-treated cells and purified chloroplasts, we believe that this component results from de novo translation in chloroplasts. The solubility of P13 was strongly promoted by Triton X-100. Its accumulation was correlated with the recovery of photosynthesis.     

RAPID AMMONIUM‐ AND NITRATE‐INDUCED PERTURBATIONS TO CHL a FLUORESCENCE IN NITROGEN‐STRESSED DUNALIELLA TERTIOLECTA (CHLOROPHYTA)1

When NH₄ ⁺ or NO₃ ^? was supplied to NO₃ ^? ‐stressed cells of the microalga Dunaliella tertiolecta Butcher, immediate transient changes in chl a fluorescence were observed over several minutes that were not seen in N‐replete cells. These changes were predominantly due to nonphotochemical fluorescence quenching. Fluorescence changes were accompanied by changes in photosynthetic oxygen evolution, indicating interactions between photosynthesis and N assimilation. The magnitude of the fluorescence change showed a Michaelis‐Menten relationship with half‐saturation concentration of 0.5 μM for NO₃ ^? and 10 μM for NH₄ ⁺ . Changes in fluorescence responses were characterized in D. tertiolecta both over 5 days of N starvation and in cells cultured at a range of NO₃ ^? ‐limited growth rates. Variation in responses was more marked in starved than in limited cells. During N starvation, the timing and onset of the fluorescence responses were different for NO₃ ^? versus NH₄ ⁺ and were correlated with changes in maximum N uptake rate during N starvation. In severely N‐starved cells, the major fluorescence response to NO₃ ^? disappeared, whereas the response to NH₄ ⁺ persisted. N‐starved cells previously grown with NH₄ ⁺ alone showed fluorescence responses with NH₄ ⁺ but not NO₃ ^? additions. The distinct responses to NO₃ ^? and NH₄ ⁺ may be due to the differences between regulation of the uptake mechanisms for the two N sources during N starvation. This method offers potential for assessing the importance of NO₃ ^? or NH₄ ⁺ as an N source to phytoplankton populations and as a diagnostic tool for N limitation.     

GROWTH AND PHOSPHORUS UPTAKE BY THE TOXIC DINOFLAGELLATE ALEXANDRIUM CATENELLA (DINOPHYCEAE) IN RESPONSE TO PHOSPHATE LIMITATION1

Alexandrium catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO₄^3?) concentrations in this environment over the 1970–1995 period. To determine if this dinoflagellate species has a competitive advantage in PO₄^3?‐limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. catenella cells along a P‐limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of ³³PO₄^3? uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from cellular P and carbon contents (Q_P and Q_C). Shifts in trends of Q_P/Q_C and Q_P per cell (Q_P·cell?1) along the DR gradient allowed the definition of successive P‐stress thresholds for A. catenella cells. The maximal uptake rate of ³³PO₄^3? increased strongly with the decrease in DR and the decrease in Q_P/Q_C, displaying physiological acclimations to PO₄^3? limitation. Concerning maximal APA per cell, the observation of an all‐or‐nothing pattern along the dilution gradient suggests that synthesis of AP was induced and maximized at the cellular scale as soon as PO₄^3? limitation set in. APA variations revealed that the synthesis of AP was repressed over a PO₄^3? threshold between 0.4 and 1 μM. As lower PO₄^3? concentrations are regularly observed during A. catenella blooms in Thau lagoon, a significant portion of P uptake by A. catenella cells in the field may come from organic compounds.     

STATE TRANSITIONS AND NONPHOTOCHEMICAL QUENCHING DURING A NUTRIENT‐INDUCED FLUORESCENCE TRANSIENT IN PHOSPHORUS‐STARVED DUNALIELLA TERTIOLECTA1

Assessments of nutrient‐limitation in microalgae using chl a fluorescence have revealed that nitrogen and phosphorus depletion can be detected as a change in chl a fluorescence signal when nutrient‐starved algae are resupplied with the limiting nutrient. This photokinetic phenomenon is known as a nutrient‐induced fluorescence transient, or NIFT. Cultures of the unicellular marine chlorophyte Dunaliella tertiolecta Butcher were grown under phosphate starvation to investigate the photophysiological mechanism behind the NIFT response. A combination of low temperature (77 K) fluorescence, photosynthetic inhibitors, and nonphotochemical quenching analyses were used to determine that the NIFT response is associated with changes in energy distribution between PSI and PSII and light‐stress‐induced nonphotochemical quenching (NPQ). Previous studies point to state transitions as the likely mechanism behind the NIFT response; however, our results show that state transitions are not solely responsible for this phenomenon. This study shows that an interaction of at least two physiological processes is involved in the rapid quenching of chl a fluorescence observed in P‐starved D. tertiolecta: (1) state transitions to provide the nutrient‐deficient cell with metabolic energy for inorganic phosphate (P_i)‐uptake and (2) energy‐dependent quenching to allow the nutrient‐stressed cell to avoid photodamage from excess light energy during nutrient uptake.     

CLONING OF A cDNA ENCODING A 66-kDa Ca2+-DEPENDENT PROTEIN KINASE (CDPK) FROM DUNALIELLA TERTIOLECTA (CHLOROPHYTA)

A cDNA clone encoding a Ca²+-dependent protein kinase (DtCPK1) with a calculated molecular mass of 65,746 Da was isolated by sequential immuno- and hybridization-screening from a cDNA library of the halotolerant green alga, Dunaliella tertiolecta Butcher (Chlorophyceae). Primary structure analysis of DtCPK1 revealed a long variable domain preceding a catalytic domain, an autoinhibitory junction domain, and a C-terminal calmodulin-like domain containing 4 EF-hand motifs. Database searches showed that DtCPK1 has a high similarity to CCK1 , a CDPK from the green alga, Chlamydomonas eugamentos Moewus . The N-terminal long variable domain of DtCPK1 contains neither the N-myristoylation motif, which is found in many CDPKs, nor the PEST motif, which is associated with rapid protein turnover and found in one CDPK subfamily. However, a putative Ca²+-dependent lipid binding domain that might be responsible for the association of cytosolic DtCPK1 with the cell membrane was identified in the variable domain. Three CDPKs, with molecular masses of 62, 54, and 47 kDa respectively, were observed in an in-gel protein kinase assay of D. tertiolecta cells extract. No change in the activities of these CDPKs were observed for up to 30 min after D. tertiolecta cells had been subjected to a hypoosmotic shock. An antibody raised against a CDPK purified from D. tertiolecta and used to isolate the DtCPK1 cDNA clone cross-reacted strongly with the 62-kDa CDPK but weakly with the 54-kDa CDPK in a Western blot, indicating that the 62-kDa CDPK is identical to DtCPK1. There was no change in the intensity of these bands after hypoosmotic shock, implying that the cellular level of the enzyme protein is not associated with hypoosmotic shock. These results indicate that CDPK is activated only by the increase in cytosolic-free Ca²+ concentration in vivo .     

CHARACTERISTICS OF PHOSPHORUS LIMITATION IN CHLAMYDOMONAS REINHARDTH (CHLOROPHYCEAE) AND ITS PALMELLOIDS1

Chlamydomonas reinhardtii Dang, was grown in a chemostat culture under phosphate limitation. The steady state concentration of phosphate was below the detection limit (< 1 μg P/L) in all runs. The cellular content of phosphorus (Q_p), polyphosphate (Q_pp) and chlorophyll a increased with increasing dilution rate, and the growth rate of the alga was described by Q_p as well as Q_pp in the Droop model. The ratio Q_pp/Q_p and the activity of alkaline phosphatase were maximal at high and low growth rates, respectively. Palmelloids of Chlamydomonas were found at high dilution rates (D > 0.12 h^?1) and became attached to the wall of the culture vessel. They differed from the vegetative stage in both chemical composition and growth rate. Their contents of phosphorus and chlorophyll a were low, as in the vegetative cells, which grew at a low growth rate, whereas the ration Q_pp/Q_p and the activity of alkaline phosphatase were comparable with those of fast growing vegetative cells. The growth rate of the palmelloids was 0.03 h^?1 whereas maximum growth rate (μ_m) for the vegetative cells was 0.21 h^?1.     

PHYSIOLOGICAL AND ULTRASTRUCTURAL RESPONSES OF CYCLOTELLA MENEGHINIANA (BACILLARIOPHYTA) TO LIGHT INTENSITY AND NUTRIENT LIMITATION1

Photosynthetic characteristics and chloroplast ultrastructure of Cyclotella meneghiniana Kütz. were quantified while the organism was simultaneously adjusting to light and nutrient stress. Cells were grown in batch culture at either low or high light intensity on medium with a nitrogen/phosphorus molar ratio of 2:1 as a control, or with nitrogen or phosphorus deleted from the medium to create nutrient deficiencies. Analysis of variance indicated that light intensity, nutrient deficiency and duration of nutrient deficiency all had significant effects on cell growth, chlorophyll (Chl) concentration/cell, cellular fluorescence capacity (CFC), chloroplast volume and thylakoid surface density. Because interactions existed among nutrient deficiency, extent of nutrient deficiency, and light intensity, all three must be considered together in order to describe accurately the physiology and chloroplast ultrastructure of the diatom. Significant correlations were found between the Chl/cell or CFC/cell and chloroplast volume and thylakoid surface density. Through an increase in Chi concentration, chloroplast volume and thylakoid surface density, the cells successfully adapted to the conditions of low light intensity even while under nutrient stress. In contrast, less Chl/cell, smaller chloroplast volume and less thylakoid surface density were found at high light intensity.     

EFFECTS OF LONG TERM EXPOSURE TO LOW TEMPERATURE ON THE PHOTOSYNTHETIC APPARATUS OF DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

The effects of long term exposure to suboptimal growth temperature on the photosynthetic apparatus of Dunaliella tertiolecta Butcher were investigated using carbon fixation rate versus irradiance curves and the variable fluorescence induction method. Carbon fixation rates per unite chlorophyll a at saturating (p^B_m) and subsaturating (α^B) irradiances were 55% and 39% lower, respectively, at 12° C than at 20° C. Chlorophyll a quotas and the spectrally averaged in vivo absorption cross section normalized to chlorophyll a (a^*) were not significantly different at these two temperatures. Analysis of the fluorescence kinetics revealed 1) no significant variations of the amount of PSII photoactive reaction centers per unit chlorophyll a, 2) a 14% decrease of the PSII quantum yield(+) and 3) a 29% decrease of the energy transfer efficiency between the light harvesting chlorophyll a pigment bed and the PSII reaction centers. The decrease in energy transfer efficiency between the antennae and the PSII reaction centers at 12° C was interpreted as a mechanism to avoid photoinhibition.     

INTERACTION OF NITROGEN FIXATION AND PHOSPHORUS LIMITATION IN APHANIZOMENON FLOS-AQUAE (CYANOPHYCEAE)1

The effect of simultaneous nitrogen fixation and phosphorus limitation on the physiological adaptation and growth performance of Aphanizomenon flos-aquae (L.) Ralfs PCC 7905 was studied in continuous culture. In the absence of ammonia, N₂ fixation occurred and the maximum growth rate (as determined in diluted batch cultures) was lower. However, no distinction could be made between the steady-state N uptake rates (based on cellular N contents) of N₂-fixing cells and cells grown with ammonia. At the higher dilution rates, the residual P concentration increased with increasing dilution rate, more so under N₂-fixing conditions, compared to the cultures grown in the presence of ammonia. More generally, the yield of biomass per consumed P, as the biomass concentration itself, decreased with increasing dilution rate, and both were lower under N₂-fixing conditions. The restricted biomass production under N₂-fixing conditions suggests that reduction of N loading may benefit lake restoration projects. The influence of N₂-fixation on the severity of P limitation is discussed in terms of metabolic control analysis. From the increase of the residual P concentration on switching from ammonium to N₂-fixing conditions, it is deduced that under N₂-fixing and P-limited conditions, control of growth is shared by N and P metabolism.     

BIOCHEMICAL AND CYTOLOGICAL EVIDENCE FOR THE STIMULATION OFCLATHRIN-COATED PIT (VESICLE) FORMATION BY EXOGENOUS FOLIC ACID IN DUNALIELLA SALINA (CHLOROPHYTA)1

The effects of two kinds of molecules, Pb²⁺ and folic acid, on the formation of clathrin-coated pits and vesicles were studied in the unicellular green alga, Dunaliella salina Teod. Measurable amounts of algal clathrin were obtained in the postmicrosomal fraction from cells treated with folic acid. In contrast, algal clathrin heavy chains were below the detection limit in the postmicrosomal fraction from control and lead nitrate-treated cells. Consistent with the biochemical evidence, electron microscopy showed more clathrin-coated pits and vesicles in folic acid-treated cells compared to control cells or cells treated with lead nitrate alone. Observations of folic acid/lead nitrate-treated cells confirmed the endocytosis of Pb²⁺ through clathrin-coated pits and vesicles. As additional evidence for clathrin in the folic acid-stimulated cells of Dunaliella salina, clathrin was isolated and, for the first time in algae, the calcium-dependent reconstitution of clathrin cages was successfully obtained in vitro.     

EFFECT OF NITROGEN AND PHOSPHORUS SUPPLY ON GROWTH AND TISSUE COMPOSITION OF ULVA FENESTRATA AND ENTEROMORPHA INTESTINALIS (ULVALES,CHLOROPHYTA)1

The chlorophyte macroalgae Ulva fenestrata (Postels and Ruprecht) and Enteromorpha intestinalis (Linnaeus) Link. were grown under various nutrient regimes in indoor semi-continuous and batch cultures. Tissue nitrogen contents ranged from 1.3–5.4% N (dry wt), whereas tissue P ranged from 0.21–0.56% P (dry wt). Growth in low nitrogen medium resulted in N:P ratios of 5–8, whereas growth in high nitrogen medium resulted in N:P ratios of 21–44. For U. fenestrata, tissue N:P < 16 was indicative of N-limitation. Tissue N:P 16–24 was optimal for growth and tissue N:P > 24 was indicative of P-limitation. Growth of U. fenestrata was hyperbolically related to tissue N but linearly related to tissue P. Phosphorus-limited U. fenestrata maintained high levels of tissue N, but N-limited algae became depleted of P. For E. intestinalis, tissue N remained at maximum levels during P-limitation whereas tissue P decreased to about 85% of maximal levels during N-limitation. Growth rates for U. fenestrata decreased faster during P-limitation than during N-limitation. Simultaneously, tissue P was depleted faster than tissue N. Our results suggest that comparing tissue N and P of macroalage grown in batch cultures is useful for monitoring the nutritional status of macroalgae.     

PHOTOACCLIMATION AND GROWTH RATE RESPONSES OF ULVA ROTUNDATA (CHLOROPHYTA) TO INTRADAY VARIATIONS IN GROWTH IRRADIANCE1

A vegetative clone of the chlorophyte macroalga Ulva rotundata was maintained in an outdoor continuous flow system under nutrient sufficient conditions and various light regimes. Step changes between 9 and 100% incident irradiance (I^o) were employed to simulate cloud passage. Temporary (1–4 h) midday (I^o)perturbations evoked net changes in growth rate (μ) and chlorophyll (chl) content. Under I_o alternating at various periodicities from 15 min to 7 h, net μ was the average of the μ under steady state 9 and 100% I^o, regardless of periodicity. However, the μ in alternating light was considerably less than μ under steady state 55% I^o(? 9%+ 100%/2), as expected based on the nonlinear shape of the μ-I relationship. Unlike μ, chl content depended primarily on the total daily irradiance, probably clue to the slower response of chl compared to photosynthetic rate. On time scales ≥ one day, chl was linearly correlated with light-regulated daily μ under both steady state and intraday fluctuating irradiance, consistent with photosynthetic feedback regulation of chl concentration.     

DISSECTING THE PHYSIOLOGICAL RESPONSE TO PHOSPHORUS STRESS IN MARINE SYNECHOCOCCUS ISOLATES (CYANOPHYCEAE)1

Marine Synechococcus is ubiquitous in aquatic environments. However, distinct phylogenetic lineages of this genus have a complex ecological distribution that is not fully explained. Here, we undertook a broad study of the phosphorus (P)–related behavior of marine Synechococcus isolates from all previously described ribotypes (sensu Fuller et al. 2003 ). A wide variability in P‐related physiology was noted among members of this genus, particularly in the utilization of organic P sources. However, some characteristics (e.g., cell size change during P limitation and the ability to accumulate polyphosphate) were largely consistent with their phylogenetic lineage and inferred ecology, with clear distinctions between oligotrophic, mesotrophic, and opportunistic lineages. Similarly, the ability to induce protein expression in response to P limitation was consistent with the presence/absence of phoB/R regulatory capacity of the corresponding strain. Taxonomic differences in P uptake, storage, and utilization strategies could explain the ubiquitous distribution of marine Synechococcus throughout the world’s oceans and explain the coexistence and/or ecological partitioning of multiple phototrophic taxa in the photic zone of tropical and subtropical oligotrophic oceans.