John G. Rueter

Iron nutrition of Trichodesmium

The diazotrophic metabolism that allows Trichodesmium to thrive in nitrogen-poor oligotrophic oceans relies on many iron-containing enzymes and proteins. The iron dependent processes in Trichodesmium and the theoretical amount of iron required for these processes are comparable to the measured iron content of colonies from the open ocean. The high iron requirement of these species is problematic in light of the limited iron delivery to open ocean systems. Trichodesmium can take up soluble forms of iron and has unique mechanisms that may allow it to use iron contained in dust particles. Their ability to add new nitrogen through nitrogen fixation and their potential for increasing the amount of biologically available iron make Trichodesmium crucial organisms in the geochemistry of tropical and sub-tropical oceans.

IRON STIMULATION OF PHOTOSYNTHESIS AND NITROGEN FIXATION IN ANABAENA 7120 AND TRICHODESMIUM (CYANOPHYCEAE)

Iron availability may limit carbon and nitrogen fixation in the oceans. The freshwater cyanobacterium, Anabaena, was used as a laboratory model for the biochemical and physiological effects of iron. Increased iron nutrition, in the range of 10−8 M to 10−6 M resulted in increases of approximately four fold in carbon and nitrogen fixation rates. Chlorophyll concentration increased, and the relative amount of in vivo fluorescence was reduced with more iron. Natural samples of Trichodesmium, collected off Barbados and incubated with increased iron for two days, showed similar effects. Trichodesmium responded to iron additions indicating that it may be Fe limited in its natural environment. These responses to iron are consistent with the biochemical roles of iron in photosynthesis and nitrogen fixation. The results are discussed in the geochemical context of the sporadic total iron input to tropical oceans and possible implications to spatial and temporal patterns of productivity.

THE EFFECT OF IRON NUTRITION ON PHOTOSYNTHESIS AND NITROGEN FIXATION IN CULTURES OF TRICHODESMIUM (CYANOPHYCEAE)1

Cultures of Trichodesmium NIBB 1067 were grown in the synthetic medium AQUIL with a range of iron added from none to 5 × 10−7 M Fe for 15 days. Chlorophyll‐a, cell counts, and total cell volume were two or three times higher in medium with 10−7 M Fe than with no added Fe. Oxygen production rate per chlorophyll‐a was over 60% higher with higher iron. Increased iron stimulated photosynthesis at all irradiances from about 12–250 μE · m−2· s−1. Nitrogen fixation rate, estimated from acetylene reduction, for 10−7 and 10−8 M Fe cultures was approximately twice that of the cultures with no added Fe. The range of rates of O2 production and N2 fixation in cultures at the iron concentrations we used were similar to the rates from natural samples of Trichodesmium from both the Atlantic, and the Pacific oceans. This similarity may allow this clone to be used, with some caution, for future physiological ecology studies. This study demonstrates the importance of iron to photosynthesis and nitrogen fixation and suggests that Trichodesmium plays a central role in the biogeochemical cycles of iron, carbon and nitrogen.

Cultures of the pelagic cyanophytes Trichodesmium erythraeum and T. thiebautii in synthetic medium

Trials for determination of culture conditions for the marine cyanophytes of Trichodesmium erythraeum and T. thiebautii were made with use of a synthetic medium. The “Aquil” medium, either with or without combined nitrogen, brought about stable growth of the two strains, T. erythraeum and T. thiebautii. However, they failed to grow in an ASP7 medium. The failure was found to be due to the toxic effect of Tris-aminomethane, the pH-buffer in this medium. Two important chemical conditions for the stable growth of Trichodesmium spp. were revealed. (1) Stable growth was supported by Ca2+ at high concentrations; in a concentration lower than 0.9 mM, cell-lysis promptly occurred, while the cells could grow without cell-lysis at Ca2+ concentrations higher than 7.5 mM even at a salinity as low as 19‰ S. Ca2+ is probably essential for the osmotic regulation in this organism. (2) Phosphate-toxicity at high concentrations was at least partly due to heavy metal(s) contaminating the reagent of inorganic phosphate. After treatment with a Chelex-100 column, phosphate concentration could be increased up to four times the previous concentrations without toxicity.

Micronutrient effects on cyanobacterial growth and physiology

Abstract Trace metals play crucial roles in the carbon and nitrogen metabolism of cyanobacteria. Physiological responses to metal limitation and toxicity in culture have shown that iron is important for photosynthesis and energy distribution in the cell while both iron and molybdenum are biochemically involved in nitrate reduction and nitrogen fixation. Nitrogen fixation is also relatively sensitive to copper toxicity. Consequently, factors that affect the supply rate, chemical speciation, or the recycling of trace metals can alter patterns of primary productivity and nitrogen metabolism. Overall, three trace metal dependent processes may contribute towards dominance: efficient use of limiting light, nitrogen fixation, and production of extracellular iron binding compounds.

Indirect aluminum toxicity to the green alga Scenedesmus through increased cupric ion activity

Additions of aluminum and copper to chemically defined media resulted in inhibition of growth of Scenedesmus and of alkaline phosphatase activity. The alkaline phosphatase activity was assayed both on commercially available purified enzyme from bacteria and on the enzyme present in whole Scenedesmus cells. The effect of metal additions was compared to the total aluminum added and to the computed free ion activities for both copper and aluminum. In all three systems (algal growth, purified enzyme, and algal enzyme) the observed toxicity with increased total aluminum was mostly due to an increase in cupric ion activity. The algal growth response was affected for the range of cupric ion activities from 10/sup -6/ to 10/sup -12/. The toxic dose response of aluminum was largely due to indirect competitive effects of Al in the medium that displaced copper from the chelator. 33 references, 4 figures.

Inhibition of carbon uptake and stimulation of nitrate uptake at low salinities in Fucus distichus (Phaeophyceae)

Inorganic carbon and nitrate uptake were examined in whole plants of Fucus distichus L. (Powell) incubated in dilutions of synthetic ocean water and media with different concentrations of Na+, K+ and Cl−. Reduction in salinity from normal seawater (33 ppt) decreased carbon uptake rate but increased nitrate uptake rate by 50% each. Substitution of K+ for Na+ at constant ionic strength decreased nitrate uptake. Substitution of K+ or mannitol for Na+ decreased carbon uptake. Neither the uptake of nitrate or carbon was changed by substituting SO42‐ for Cl−. Ionophores, valinomycin and monensin, inhibited both nitrate uptake and carbon fixation from 20 to 70% of control rates. The stimulation of nitrate uptake at low salinity may be beneficial to plants in estuarine tidal environments in which nitrate is supplied by the fresh water source.

The effects of changes in both the abundance of nitrogen and phosphorus and their ratio on Lake Okaro phytoplankton, with comment on six other central volcanic plateau lakes

DAVID R. S. LEAN STUART F. MITCHELL FRANCES R. PICK JOHN G. RUETER MALCOLM T. DOWNES GEORGE W. PAYNE STUART E. PICKMERE EDWARD WHITE PAUL H. WOODS National Water Research Institute Box 5050, Burlington, Ontario Canada L7R 4A6 Department of Zoology University of Otago Dunedin, New Zealand Department of Biology Ottawa University Ottawa, Ontario, Canada K1N 6N5 Department of Biology Portland State University P.O. Box 751, Portland Oregon, U.S.A. 97207 Taupo Research Laboratory Department of Scientific and Industrial Research P.O. Box 415, Taupo, New Zealand

EFFECT OF COPPER ON GROWTH, SILICIC ACID UPTAKE AND SOLUBLE POOLS OF SILICIC ACID IN THE MARINE DIATOM, THALASSIOSIRA WEISFLOGII (BACILLARIOPHYCEAE)1

The toxicity of Cu to Thalassiosira weissflogii (Grunow) was investigated, focusing on the internal soluble pool of silicic acid. Silicic acid uptake and growth rates were found to be functions of both the cupric ion activity and the concentration of silicic acid in the growth medium. The soluble pool of Si per cell depended on the balance between the uptake rate and the division rate. The soluble pool in non‐dividing cultures reflected simply the uptake rate (and inhibition by copper of the uptake rate), but in dividing cultures the soluble pools had complex patterns with time depending on uptake rates and timing of division. Intracellular soluble pools of silicic acid are a good indicator for the relative inhibition of uptake and growth processes.

Reducing surface accumulation of Aphanizomenon flos-aquae using wetland water to increase cellular turgor pressure and interfere with buoyancy regulation

Abstract Rouhe AC, Rueter JG. Reducing surface accumulation of Aphanizomenon flos-aquae using wetland water to increase cellular turgor pressure and interfere with buoyancy regulation. Lake Reserve Manage. 34:426–446. The ability to regulate buoyancy (sinking and floating) using cellular gas vesicles is a unique characteristic that allows many common bloom-forming cyanobacteria to accumulate at water surfaces and dominate systems. Typical control and management strategies of cyanobacterial blooms include nutrient manipulation and phosphorus reduction, which are effective but do not reduce the advantage of buoyancy control. Since buoyancy control is based upon a mechanism driven by photosynthesis, along with environmental conditions that trigger vesicle formation and ion exchange, buoyancy regulation can be influenced by manipulating extracellular conditions. In this study, we manipulated extracellular conditions using wetland water and additions of potassium, sodium, and calcium in small-scale lab experiments containing Aphanizomenon flos-aquae from Upper Klamath Lake, Oregon. The results indicate a target mixture of 10% wetland water reduces surface accumulation, increases cellular turgor pressure (a measure of the ability of gas vesicle–forming cells to control buoyancy), and leads to fewer cyanobacterial filament rafts near the surface of the water column. By adding ions at the same concentration as the target wetland mixture, similar results were found. This research represents the basis of a possible strategy for mitigating surface blooms of buoyant cyanobacteria in lakes using wetland water and/or ion additions that could be used in tandem with nutrient manipulation and phosphorus reduction.