This comprehensive literature review of the phosphorus nutrition and metabolism of eukaryotic microalgae deals sequentially with (1) extracellular P-compounds available for algal utilization and growth; (2) orthophosphate uptake mechanisms, kinetics, and influence from environmental variables; (3) phosphatase-mediated utilization of organic phosphates involving multiple enzymes, induction and cellular location of repressible and irrepressible phosphatases, and their role in growth physiological processes; (4) intracellular phosphate metabolism covering diversity of phosphometabolites. ATP-linked energy regulation, polyphosphate pools and storage roles, phospholipids and phospholipases; (5) steady-state and transient-state models relating phosphate utilization to growth; (6) ecological aspects covering manifestations of phosphorus limitation, interspecific competition for phosphonutrients among microorganisms, and current views on phosphorus cycling and turnover in aquatic ecosystems. Although concentrating on the microalgae, the review often points out sounder conclusions drawn from bacteria and fungi, and includes specific macroalgae in considering certain subtopics where such algae were better investigated and provided a good basis for comparison with the microalgae.

The utilization of inorganic and organic phosphorous compounds as nutrients by eukaryotic microalgae: a multidisciplinary perspective: part 1

The lipid content of various phytoplankton species was measured in response to nitrogen and silicon limitation and over the cell cycle in synchronized cultures. In a survey of 30 species it was found that during log-phase growth, green algae contained an average of 17.1% total lipids (% of total dry weight), whereas diatoms contained an average of 24.5%. Nitrogen deprivation for 4 to 9 days resulted in 2- to 3-fold increases in the lipid content of green algae, whereas both increases and decreases were noted in diatoms, depending on the species. The greatest lipid content measured in the study was 72% in Monallantus salina (strain GSB Sticho) which had been deprived of nitrogen for 9 days. Nitrate replenishment in a nitrogen starved culture of Oocystis polymorpha Groover & Bold showed that the excess cellular lipids do not rapidly disappear during recovery, until cell division occurs.



A silicate deprivation experiment with Cyclotella cryptica Reimann, Lewin & Guillard (strain 7c) showed an increase in the total cellular lipid fraction from. 30 to 42% of dry weight within 6 h of the onset of silicon limitation, while the mass of lipid material per cell doubled within 12 h. The total lipid fraction in O. polymorpha was found to remain constant over the cell cycle in synchronized cultures regardless of the light regime. The data presented provided the first internally consistent study of phytoplankton lipids for a wide range of species and several growth conditions.

Phytoplankton lipids: interspecific differences and effects of nitrate, silicate and light‐dark cycles1

The biological source of sedimentary organic matter can be inferred from detailed chemical studies on the structure of individual molecules extracted from sediments. These inferences are drawn from established relationships between biological source materials and diagenetically altered compounds (de Leeuw and Largeau, this volume, Chapter 2). A second method for inferring the biological source and the ecological setting in which organisms existed is with isotopic tracers of carbon, nitrogen, oxygen, hydrogen, and sulfur in organic matter and inorganic substances that have been processed by living organisms. Stable isotope compositions of bulk organic matter have integrative signals from processes that have occurred over the life of the organism, whereas those of individual compounds can record specific events in life. In this chapter, we will review recent advances in biological isotope fractionations of the light stable isotopes and attempt to offer an interpretation of processes that affected the isotopic signature of organic substances in living organisms that were preserved in the fossil record.

Isotope Fractionation during Primary Production

Continuous cultures of three marine phytoplankton species, Phaeodactylum tricornutum, Dunaliella tertiolecta, and Monochrysis lutheri, were monitored for changes in alkalinity of the culture medium resulting From NO, and NHa+ uptake. Uptake of NO,caused an increase in alkalinity, whereas uptake of NH,+ produced a decrease. These results are consistent with the type of schematic equation proposed by Redfield, Ketchum, and Richards for photosynthetic assimilation of inorganic nitrogen, in which NO, uptake is balanced by OHproduction and NHa+ uptake leads to H+ generation. These reactions suggest active uptake of nitrogen species by microbes. We have been unable to demonstrate the exact stoichiometry of this relationship, and the role of P uptake in the alkalinity change is unclear. An offset in the data, functionally equivalent to the production of some strong acid, may be due to reactions on the walls of the vessel, active uptake of cations, or extrusion of H’ ions by the growing cells. An understanding of the oceanic CO2 system is important in many branches of marine chemistry and biolo,gy. Experimentally, this may be approached through measurement of any two of the four variablcs pH, alkalinity, pCOa, and total COz, and from any two of these properties the others can be calculated (Skirrow 1965). Many recent data have been obtained by the potentiometric titration technique ( Dyrsscn 1965; Edmond 1970) that enables the alkalinity and total COz to be measured in a single sample. The alkalinity of scawater is defined as the number of equivalents of strong acid required to titrate 1 liter of seawater to the C02-HC03end point. Analytically, this is equivalent to the sum of the concentrations of the anions of carbonic and other weaker acids. Alkalinity is thus inherently associated with charge balance ( Stumm and Morgan 1970), and the addition or removal of neutral CO2 during respiration or photosynthesis has no cffcct on this property. All this is frequently taken to mean that the photosynthetic or decomposition processes occurring in aquatic environments do not generate alkalinity changes. This is ’ Contribution No. 3595 from the Woods IIole Oceanographic Institution. This research was supported by NSF grants GA-22292 and GX-33295 (P.G.B. ) and ERDA contract AT( 11-l )2532 ( J.C.G. ) . by no means correct. Goldman c t al. (1972) have pointed out that uptake of N03during photosynthesis generates strong base, whereas NH4+ assimilation leads to acid production. Brewer et al. ( 1975) have discussed the reverse effect in which the dccomposition of marine organic matter csscntially leads to the liberation of nitric acid. This strong acid reacts with carbonate ion derived from calcium carbonate dissolution, thus leaving an excess of calcium over that predicted from observed alkalinity changes. These effects have been inferred for many years (Trelease and Trelease 1935; Cramer and Myers 1948; Rcdfield ct al. 1963; Richards 1965; Berner et al. 1970; Gaines and Pilson 1972) and indeed are implicit in the Redficld-Ketchum-Richards phytoplankton equations. Yet, as far as we are aware, these phenomena have not been adequately documented and no cxpcrimental prooE cxis ts. Here, we report our mcasurcmcnts of alkalinity changes during the growth of phytoplankton on both NOaand NI-IJ+ as nitrogen sources. We thank J. M. Edmond and F. Morel for their critical review and R. Smith, S. Kadar, A. Fleer, and R. Carbon for their technical assistance.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1976.21.1.0108

Alkalinity changes generated by phytoplankton growth1

Diatoms, but not flagellates, have been shown to increase rates of nitrogen release after a shift from a low growth irradiance to a much higher experimental irradiance. We compared NO3− uptake kinetics, internal inorganic nitrogen storage, and the temperature dependence of the NO3− reduction enzymes, nitrate (NR) and nitrite reductase (NiR), in nitrogen-replete cultures of 3 diatoms (Chaetoceros sp., Skeletonema costatum, Thalassiosira weissflogii) and 3 flagellates (Dunaliella tertiolecta, Pavlova lutheri, Prorocentrum minimum) to provide insight into the differences in nitrogen release patterns observed between these species. At NO3− concentrations <40 μmol-N·L−1, all the diatom species and the dinoflagellate P. minimum exhibited saturating kinetics, whereas the other flagellates, D. tertiolecta and P. lutheri, did not saturate, leading to very high estimated K  s values. Above ∼60 μmol-N·L−1, NO3− uptake rates of all species tested continued to increase in a linear fashion. Rates of NO3− uptake at 40 μmol-N·L−1, normalized to cellular nitrogen, carbon, cell number, and surface area, were generally greater for diatoms than flagellates. Diatoms stored significant amounts of NO3− internally, whereas the flagellate species stored significant amounts of NH4+. Half-saturation concentrations for NR and NiR were similar between all species, but diatoms had significantly lower temperature optima for NR and NiR than did the flagellates tested in most cases. Relative to calculated biosynthetic demands, diatoms were found to have greater NO3− uptake and NO3− reduction rates than flagellates. This enhanced capacity for NO3− uptake and reduction along with the lower optimum temperature for enzyme activity could explain differences in nitrogen release patterns between diatoms and flagellates after an increase in irradiance.

Comparisons of nitrate uptake, storage, and reduction in marine diatoms and flagellates

Field studies of whole natural phytoplankton communities from Knight Inlet, B. C., Canada and laboratory cultures of the diatom Skeletonema costatum indicate inorganic carbon fixation may be temporarily suppressed following 10 to 15% enrichment with NO
 3
 -
 or NH
 4
 +
 . (This effect is suggested to be due to competition between inorganic carbon and nitrogen for adenosine triphosphate (ATP), and is reduced when chlorophyll a is increased intracellularly after 6 to 8 h.) Results imply that the source of ATP for nitrate uptake is primarily from Photosystem I (cyclic photophosphorylation) in the presence of light. It would appear that a transient nutrient-adaptive response occurs upon addition of extracellular nitrogen.

Nitrate uptake in marine phytoplankton: Energy sources and the interaction with carbon fixation

Seven species of marine phytoplankton were assayed for the presence of a NO3−,CI−-activated ATPase, thought to be associated with the cell membrane. Only the single dinoflagellate tested, Amphiclinium carterae, failed to show ATPase activity, while the specific activity of the enzyme ranged over one order of magnitude in the other species examined. It is suggested that the enzyme is primarily responsible for the active transport of NO3− across the plasmalemma and furthermore the Km for NO3− activation of the enzyme is physiologically manifested by Ks values for NO3− uptake by whole cells. The enzymatic mechanism may explain the observed Michaelis-Menten kinetics for NO3− uptake.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1975.20.3.0412

Nitrate uptake in marine phytoplankton: Comparison of half-saturation constants from seven species1

SUMMARY

A membrane-bound (nitrate, chloride)-activated AT Pase was found in the neritie diatom, Skeletonema costatum (Grev.) Cleve. The enzyme is suggested to translocate NO3− across the plasmalemma, against a concentration gradient. The Km of the enzyme with respect to NO3− is ca. 0.9 × 10−6 M, and is in close agreement with the reported K8 for NO3− uptake by the whole cell.

Paul G. Falkowski

Papers

Nitrate uptake in marine phytoplankton: Energy sources and the interaction with carbon fixation

Nitrate uptake in marine phytoplankton: Comparison of half-saturation constants from seven species1

Nitrate uptake in marine phytoplankton: (nitrate, chiloride)-activated adenosine triphosphatase from skeletonema costatum (bacillariophyceae)1,2