Epiphytic bacteria on the Antarctic ice diatom Amphiprora kufferathii Manguin cleave hydrogen peroxide produced during algal photosynthesis.

The Antarctic ice diatom Amphiprora kufferathii Manguin is always accompanied by epiphytic bacteria in its natural habitat. To investigate the nature of this relationship, axenic cultures of A. kufferathii were obtained by ampicillin treatment. Diatom cultures without bacteria were less dense. The bacteria were shown to consume hydrogen peroxide produced by the diatom during photosysnthesis and algal photosynthesis after a hydrogen peroxide shock recovered faster in the presence of bacteria. Three proteobacterial strains isolated from a culture of A. kufferathii were phylogenetically affiliated with the alphaproteobacterial genus Sulfitobacter, the gammaproteobacterial genus Colwellia, and the genus Pibocella of the Bacteriodetes. Native protein gel electrophoresis and enzyme activity staining revealed the presence of superoxide dismutase and glutathione reductase in the isolated bacteria and in A. kufferathii cultures. Catalase was detected in bacterial extracts but not in axenic cultures of A. kufferathii. These observations indicate that the epiphytic bacteria make a significant contribution to the diatom's antioxidative defences. The relationship between the bacteria and A. kufferathii seems to be beneficial for both partners and enhances growth of Amphiprora in the sea ice.

The energy requirements of pH homoeostasis define the limits of pH regulation--a model.

The regulation of intracellular pH of Platymonas subcordiformis cells is investigated with 31P-NMR spectroscopy at various external pH values. The limits of pH homeostasis differ between respiring cells and cells solely glycolyzing. The former retain their normal cytoplasmic pH for external pH values from 5 to more than 12, while in the latter intracellular pH is less stable below external pH 6, and external pH of more than 11 causes hydrolysis of intracellular polyP. The power necessary to maintain a stable intracellular pH is calculated from the electrochemical potential and H+/OH- flux rates across the cell membrane. H+/OH- transport across the membrane by diffusion as well as through hydrogen-bonded chains is considered. Comparison of the minimal power necessary to keep intracellular pH stable at various external pH values by ATP consuming processes with the estimated power available to aerobic and anaerobic cells in the dark shows that different energy turnover may explain the different behaviour of the cells when exposed to extreme pH values.

D-Mannitol dehydrogenase and D-mannitol-1-phosphate dehydrogenase in Platymonas subcordiformis: some characteristics and their role in osmotic adaptation.

D-Mannitol-1-phosphate dehydrogenase (EC 1.1.1.17) and D-mannitol dehydrogenase (EC 1.1.1.67) were estimated in a cell-free extract of the unicellular alga Platymonas subcordiformis Hazen (Prasinophyceae), D-Mannitol dehydrogenase had two activity maxima at pH 7.0 and 9.5, and a substrate specifity for D-fructose and NADH or for D-mannitol and NAD(+). The K m values were 43 mM for D-fructose and 10 mM for D-mannitol. D-Mannitol-1-phosphate dehydrogenase had a maximum activity at pH 7.5 and was specific for D-fructose 6-phosphate and NADH. The K m value for D-fructose 6-phosphate was 5.5 mM. The reverse reaction with D-mannitol 1-phosphate as substrate could not be detected in the extract. After the addition of NaCl (up to 800 mM) to the enzyme assay, the activity of D-mannitol dehydrogenase was strongly inhibited while the activity of D-mannitol-1-phosphate dehydrogenase was enhanced. Under salt stress the K m values of the D-mannitol dehydrogenase were shifted to higher values. The K m value for D-fructose 6-phosphate as substrate for D-mannitol-1-phosphate dehydrogenase remained constant. Hence, it is concluded that in Platymonas the D-mannitol pool is derectly regulated via alternative pathways with different activities dependent on the osmotic pressure.

Seasonal changes of ionic concentrations in the vacuolar sap of Chara vulgaris L. growing in a brackish water lake.

The composition of the vacuolar sap of Chara vulgaris growing in a brackish water lake was estimated weekly over 2 years (1984-1985). The ionic concentrations of the main cations Na+, K+, Ca2+, and Mg2+ and the anion Cl- varied depending on cell age, developmental state, and season. The average of all measurements (in mM) was Na+: 35, K+: 106, Ca2+: 7, Mg2+: 23, Cl-: 101, SO 2-4 : 20, and PO 3-4 : 5. At the onset of growth in May/June the ionic content was lower compared to the mean value for the year, steadily increasing until it reached its maximum above the annual mean in winter. During the period of fructification (sexual reproduction: formation of antheridia and oogonia), when up to 100 mM sucrose was accumulated in the vacuolar sap, ionic content was lowest. This resulted in a fairly constant osmotic potential throughout the year. Mg2+ and Ca2+ concentrations were correlated with the physiological age of the cells.

OSMOTIC ADJUSTMENT IN MARINE EUKARYOTIC ALGAE: THE ROLE OF INORGANIC IONS, QUATERNARY AMMONIUM, TERTIARY SULPHONIUM AND CARBOHYDRATE SOLUTES: I. DIATOMS AND A RHODOPHYTE.

The unicellular marine algae, Phaeodactylum tricornutum Bohlin, Cyclotella cryptica Reimann and Cyclotella meneghiniana Kützing (Bacillariophyceae) and Porphyridium aerugineum Geitler (Rhodophyceae) synthesized and accumulated glycine betaine and proline in response to increases of the NaCl concentration (150 to 1000 mol m-3 NaCl) of the growth medium. C. cryptica and C. meneghiniana also synthesized and accumulated homarine (N-methyl picolinic acid betaine). Both P. tricornutum and P. aerugineum synthesized increasing amounts of intracellular glycerol and P. aerugineum also formed the heteroside, floridoside [O-α-D-galactopyranosyl (1 → 2)-glycerol], in response to the elevated salinities. No major low molecular weight carbohydrates were found in Cyclotella. Sucrose was not detected in the algal extracts. Only P. tricornutum synthesized the tertiary sulphonium compound, ß-dimethylsulphoniopropionate (DMSP), and the quantity of this solute in the alga was dependent on the amount of NaCl in the medium. Intracellular K+ concentrations in the algae were three to six times greater than those of Na+ . Increases of the salinity of the media led to the uptake and accumulation of K+ by the cells, and smaller increases of Na+ and Cl-1 and loss of intracellular NO3 - . The inorganic cations Na+ and K+ , with their accompanying anions, and the estimated organic solutes could largely account for the osmotic balance of P. tricornutum and P. aerugineum.

OSMOTIC ADJUSTMENT IN MARINE EUKARYOTIC ALGAE: THE ROLE OF INORGANIC IONS, QUATERNARY AMMONIUM, TERTIARY SULPHONIUM AND CARBOHYDRATE SOLUTES: II. PRASINOPHYTES AND HAPTOPHYTES.

The effects of steady state salinities (150 to 700 mol m-3 NaCl) on the growth rates and intracellular solutes of the prasinophyte algae Tetraselmis chui Butcher and Prasinocladus Kuckuck and the prymnesiophyte algae, Prymnesium parvum Carter and Ruttnera spectabilis Geitler, are described. Maximum growth rates were reached in media approximating to the NaCl concentration of oceanic waters (about 500 mol m-3 ). The following intracellular organic solutes paralleled the increases of external salinity: the tertiary sulphonium compound ß-dimethylsulphoniopropionate (DMSP) in T. chui, Prasinocladus, P. parvum and R. spectabilis; the polyhydric alcohol, mannitol, in T. chui, Prasinocladus and R. spectabilis; the quaternary ammonium compounds (QACs), glycine betaine and homarine, in T. chui and Prasinocladus. QACs were not detected in P. parvum and R. spectabilis. An unknown polyol, which may be the cyclitol, 1,4/2,5 cyclohexanetetrol, was synthesized by P. parvum and R. spectabilis and in addition P. parvum contained significant concentrations of glucose. Sucrose was not detected in the algal extracts. Proline was an insignificant osmoticum in all the algae. Increases of the media NaCl concentration led to the uptake and accumulation of K+ in T. chui and Prasinocladus, with smaller increases of Na+ and Cl- . The intracellular K+ concentrations in the prasinophyte algae were about five times greater than those of Na+ . The inorganic cations Na+ and K+ , and their accompanying anions, and the organic solutes found could largely account for the osmotic balance of T. chui and Prasinocladus. The inorganic ions in P. parvum and R. spectabilis were not determined.

The role of ß-dimethylsulphoniopropionate, glycine betaine and homarine in the osmoacclimation of Platymonas subcordiformis.

The tertiary sulphonium compound, ß-dimethylsulphoniopropionate (DMSP) and the quaternary ammonium compounds glycine betaine and homarine are important osmotica in Platymonas subcordiformis cells. Following hypersaline stresses the compounds were accumulated after a lag period of 3 h and equilibrium concentrations were reached 6 h later. In contrast to these organic solutes, mannitol was synthesised immediately and equilibrium concentrations were reached within 90 min. Hyposaline stresses induced losses of the organic solutes from the cells. The ions K(+), Na(+), Cl(-) and the above organic solutes can account for the osmotic balance of the cells.

Vacuolar and cytoplasmic pH, ion composition, and turgor pressure in Lamprothamnium as a function of external pH.

Ionic responses to alteration in external and internal pH were examined in an organism from a marine-like environment. Vacuolar pH (pH(v)) is about 4.9-5.1, constant at external pH (pH(o)) 5-8, while cytoplasmic pH (pH(c)) increases from 7.3 to 7.7. pH(c) regulation fails above pH(o) 9, and this is accompanied by failure of turgor regulation. Na(+) increases above pH(o) 9, while K(+) and Cl(-) decrease. These changes alone cannot however explain the alterations in turgor. Agents known to affect internal pH are also tested for their effect on ion relations.

Photosynthesis and respiration of Griffithsia monilis (Rhodophyceae): Effect of light, salinity, and oxygen.

The giant-celled alga Griffithsia monilis has a low light compensation point and saturates photosynthesis at 60-90 µmol photons m(-2)s(-1) (oxygen evolution and CO2 fixation). Under dark and low light intensities (14)C is preferentially incorporated into amino acids (mainly aspartate and alanine). With increasing light a gradual change was observed and, under light saturation, compounds of the anionic fraction (digeneaside and hexosephosphates) were the most strongly labeled compounds, together with the amino acids glycine and serine. To a large extent (30-40% of the total) (14)C was fixed into EtOH-insoluble products, the hydrolysates of which consisted mainly of glucose and mannose. In the steady state the rates of photosynthesis and respiration decreased with increasing salinity. Changes in the rates after hyperosmotic shocks were less severe in cells adapted to high salinities. Photorespiration exists in Griffithsia: Glycine and serine are the major labeled compounds in O2-saturated media.

Coordination of ionic relations and mannitol concentrations in the euryhaline unicellular alga, Platymonas subcordiformis (Hazen) after osmotic shocks.

Following small hypo-osmotic shocks, ion concentrations (Na(+), K(+), Cl(-)) in Platymonas subcordiformis decreased; this was due mainly to an increase of cell volume. With larger hypo-osmotic stresses, the decrease of ion concentration continued and, additionally, extrusion of mannitol was observed. The ion and mannitol concentrations were not regained after 240 min. In contrast, following hyperosmotic shocks, the ion concentrations increased transitorily during the first 20-40 min. The same was true for K(+) following small hyperosmotic stresses and for Na(+) and - partially - Cl(-) with larger shocks. Large hyperosmotic stresses caused permanent accumulation of mannitol, which levelled off after 60-80 min. Thus the transient increase of ions bridged the concentration gap until mannitol was accumulated to a high enough concentration to account for the osmotic adaptation of Platymonas, together with a basal level of the ions K(+), Na(+), Cl(-).

Ion composition of unicellular marine and fresh-water algae, with special reference to Platymonas subcordiformis cultivated in media with different osmotic strengths.

Ion compositions (K+, Na+ Mg2+, Ca2+, Cl-, phosphate) of the euryhaline algae, Platymonas subcordiformis, Chlorella salina, grown in media with a salinity range from 0.1 to 0.6 M NaCl and of the fresh-water algae, Ankistrodesmus braunii and Scenedesmus obliquus, were compared. Enhancement of ion concentrations with increasing salinity in Platymonas was attributed largely to decreasing cell volume. In both the euryhaline algae, Na+ and - partially - Cl- content per cell increased significantly with rising salinity. The contents per cell of the other ions were not affected. Considering the relevance of ions and mannitol (Platymonas) and proline (Chlorella) as osmotically active particles, it was found that the ions alone maintained osmotic balance with low external salinity. With increasing salinity the organic compounds contributed up to 20-30% of the cellular solute potential. The main cation, K+, was the main contributor to the osmotic balance; the accumulation of organic compounds as well as of Na+ and Cl- contributes further to the ability of the algae to adapt to high salinity. The results confirm the hypothesis of low Cl- concentrations in nonvacuolate cells in comparison to vacuolate cells.