Effects of light fluctuations on the growth and productivity of Antarctic diatoms in culture

Summary This work shows that the low division rates observed in diatoms in Antarctic waters seem to be due to conditions of irradiance rather than to the low temperature: low light intensity and light fluctuations are two factors which depress the division rate of diatoms. However, with regard to the productivity, Antarctic diatoms seem well-adapted to their turbulent environment. Cells grown in alternating periods of light and dark, notably a 2:2 regime which simulates conditions of vertical mixing, reach a higher rate of productivity than algae grown in continuous light. This difference may be due to the better use of light energy observed in the former group. In the Antarctic Ocean, which is characterized by frequent mixing of water masses, this increased efficiency of light utilization could be a way of adaptation, allowing the algae to overcome the restraints imposed by low light and low temperature, and to reach a higher productivity than expected. The low values of I_k and I_max as well as the absence of detectable photoinhibition indicate that Antarctic diatoms are capable to sustain their maximum primary production rate over a wide range or irradiance levels. On the other hand, the highest productivity in 2:2 regime shows that these species are more efficient when grown under fluctuating light. These results lead us to assume that the Antarctic species are well-adapted to live in the extreme conditions of light encountered in Antarctic Ocean: low irradiance and alternance of low and high light intensities.     

Studies on the growth of riverainCladophora in culture

Summary Techniques were developed for studying the effects of environmental factors on the growth in culture ofCladophora glomerata from flowing waters.Cladophora still attached to rocks was transferred from the river to a laboratory stream and incubated there for 4 days under standard conditions. Small pieces of this material were cut off, cleaned, and used as inocula for shake culture experiments. These experiments were mostly designed to test the effect of various agents which have been widely quoted, in literature based on field observations, as limiting the growth ofCladophora. The alga is particularly sensitive to copper and zinc among the metals tested, and to DOBS-055, a soft detergent, among the detergents tested. The experimental results support the hypothesis that the alga may occasionally be limited by high natural iron concentrations, but not that it is so sensitive to high temperature that this factor alone would often limit its growth in British rivers.     

Photosynthetic energy conversion under extreme conditions--I: important role of lipids as structural modulators and energy sink under N-limited growth in Antarctic sea ice diatoms

The availability of dissolved nutrients such as nitrate under extreme low temperatures is a strong determinant in the development and growth of ice diatoms. Consequently we investigated regulation of photosynthesis in a mixed culture of three diatom species, which grew in chemostats at -1 degrees C, 15 micromol photons m(-2) s(-1) under N-limitation. When nitrogen is limiting, pigment-protein complexes are one of the most affected structures under low-light conditions. The loss of integral polar thylakoid components destabilized the bilayer structure of the membrane with consequences for lipid composition and the degree of fatty acid desaturation. N-Limitation caused a decrease in monogalactosydiacylglycerol (MGDG) and a simultaneous increase in bilayer forming digalactosyldiacylglycerol (DGDG). Their ratio MGDG:DGDG decreased from 3.4 +/- 0.1 to 1.1 +/- 0.4, while 20:5 n-3 fatty acids of chloroplast related phospholipid classes such as phosphatidylglycerol (PG) increased under N-limitation. These data reveal that lipids are important components, required to sustain membrane structure under a deficiency of integral membrane bound proteins and pigments. Nonetheless, energy conversion at photosystem II is still affected by N-limitation despite this structural regulation. Photosynthetic quantum yield (F(v)/F(m)) and electron transport rates decreased under N-limitation caused by an increasing amount of electron acceptors (second stable electron acceptor = Q(B)) which had slower reoxidation kinetics. The energy surplus under these conditions is stored in triacylglycerols, the main energy sink in Antarctic sea ice diatoms under N-limitation.     

The influence of carbon dioxide-depletion on growth and sinking rate of two planktonic diatoms in culture

Growth in relation to CO₂-depletion and CO₂-enrichment was investigated for the freshwater diatoms Asterionella formosa and Fragilaria crotonensis in batch cultures. Algal concentration and pH were measured during growth cycles, and inorganic carbon quantities determined by potentiometric Gran titrations and from pH-alkalinity relationships. After the primary growth with CO₂-depletion and pH increase, successive CO₂-enrichments induced further such cycles and produced a final three- to fivefold increase in algal biomass over that of unenriched controls. The extent of CO₂-depletion, and pH rise, was greater in later cycles, indicative of some cellular adaptation. Values of pH reached 9·7 for Asterionella and 9·9 for Fragilaria. The lowest residual quantities of free CO₂ were 0·1 and 0·03 μmol 1^-1 for Asterionella and Fragilaria respectively, which were less than 0·05% of the corresponding residual quantities of total CO₂. The primary limitation of CO₂-uptake and growth was probably related to the concentration of free CO₂, given the relative excess of other major nutrients (N, P, Si) in he media used. Limited of CO₂-uptake could be restored without CO₂ additions if the CO₂ present was redistributed between its several forms (increasing free CO₂) by the addition of strong acid, although growth was still restricted.

Limitation of CO₂-uptake, either by CO₂-depletion or the addition of an inhibitor of photo-synthesis (DCMU), increased the sinking rate of Asterionella cells from 0·3 to 1 m day^-1. The possible ecological implications of CO₂-pH-growth and CO₂-pH-buoyancy relationships are discussed, which may contribute to the frequent paucity of diatoms during summer in manv productive lakes.     

Studies on the growth of Xanthophyceae in pure culture

Ohne ZusammenfassungTeilergebnisse aus der Dissertation Licht- und lektronenmikroskopische Untersuchungen zur Morphologie und Cytologie von Proteus vulgaris der Mathem.-Naturwiss. Fakultät der Universität Göttingen 1957.     

Studies on the growth of Xanthophyceae in pure culture

Ohne ZusammenfassungTeilergebnisse aus der Dissertation Licht- und elektronenmikroskopische Untersuchungen zur Morphologie und Cytologie von Proteus vulgaris der Mathem.-Naturwiss. Fakultät der Universität Göttingen 1957.     

Removal of inhibitors of bacterial growth by dialysis culture.

Dialysis culture was used to investigate the extent to which growth inhibition in bacterial cultures may be caused by accumulation of metabolites. Escherichia coli B was grown in a glucose/salts medium. A concentrated nutrient solution was pumped at a constant rate into the growing culture to ensure that growth was not limited by exhaustion of nutrients. In this way the only difference between growth conditions in dialysis and non-dialysis cultures was the transfer of dialysable metabolites from the culture vessel to the reservoir in the dialysis culture system. By adjusting the glucose concentration in the feed and maintaining a constant rate of feeding, glucose-limited growth could be achieved. Under these conditions, with oxygen in excess, bacterial yields of 140 to 150 g dry wt l-1 were obtained in dialysis culture compared with 30 to 40 g l-1 in non-dialysis culture. The high yields in dialysis culture depended on the removal of end-products of glucose metabolism. Growth inhibition was demonstrated to be the result of the combined influence of acetate, lactate, pyruvate, succinate, propionate and isobutyrate in concentrations found at the end of growth in non-dialysis cultures of Escherichia coli B.     

Modelling Si-N-limited growth of diatoms

A mechanistic model for silicon (Si) physiology is developed,interfaced with a model of nitrogen (N) physiology, which iscapable of simulating the major documented facets of Si–Nphysiology in diatoms. The model contains a cell cycle componentthat is involved in regulating the timing of the synthesis ofvalves, girdles and setae. In addition to reproducing the timingof diatom cell division within a light–dark cycle, themodel simulates the following features seen in real diatoms.Synthesis of valves only occurs during G₂ interphase and M,while the girdles and (if appropriate) setae are synthesizedduring G₁. Si stress alone results in a loss of setae, followedby a thinning of the valves in successive generations untila minimum Si cell quota is attained. After this point, the durationof G₂ increases and growth is Si limited. Concurrently, thecarbon (C) cell quota increases, offering the capability tosimulate the documented increase in sinking rates with Si stress.N stress alone results in an increase in the duration of G₁and G₂ interphases, and high Si cell quotas. From this complexmodel, which must be run for arrays of subpopulations to simulatenon-synchronous growth, a simpler model is developed. This iscapable of reproducing similar growth dynamics, although withno reference to component parts of the frustule. When alliedto a photoacclimative submodel, a prediction of the model isthat diatoms starved of Si will release increased amounts ofdissolved organic C because cell growth is halted more rapidlythan the photosystems can be degraded.     

Studies on the growth of Cladophora glomerata in laboratory continuous-flow culture

Cladophora glomerata grown in continuous-flow culture was found to have optimal specific growth rate (μ) at, or near, 20°C. Specific growth rate increased linearly with increased duration of illumination per day up to 24h, and increased light intensity up to 6000 lx. Undissociated ammoniacal nitrogen (0·185 mg 1^-1) reduced μ to 50% of that at 0·010 mg 1^-1: 0·077–1·057 mg NO₂-N1^-1 and 7·2–15·2 mg NO₃-N1^-1 had no significant effect on μ. At 4·9 mg PO₄-P1^-1, μ was 48% of that at 1·9 mg1^-1. The critical medium PO₄-P concentration was less than 0·098 mg1^-1. Specific growth rate was reduced to 50% of that in the based medium by 0·036 mg Cu1^-1, 0·070 mg Zn1^-1 and 1·03 mg Pb1^-1. Results are discussed in the context of the natural distribution of the alga in the field situation.     

Light-temperature interactions on the growth of Antarctic diatoms

Summary The combined effect of various temperatures and light intensities on the growth of seven species of antarctic diatoms in culture has been studied. With the exception of Chaetoceros deflandrei whose thermal tolerance is fairly good, these obligatory psychrophils cannot survive in temperatures above 6° to 9° C. Their mean growth rate is relatively low, between 0.24 div d^–1 for Corethron criophilum and 0.63 div d^–1 for C. deflandrei. Regardless of light intensity, growth rate increased with the temperature to reach a maximum between 3° and 5° C. The highest rates were obtained between 115 and 220 mol m^–2 s^–1 with 0.38 div d^–1 for C. criophilum, 0.56 div d^–1 for Synedra sp. and between 0.71 and 0.88 div d^–1 for the other 5 species. A reduction in light intensity from 220 to 46 mol m^–2 s^–1 slowed growth by nearly 50%. These results suggest that the combined effect of temperature and light is one of the factors involved in the limitation of antarctic phytoplankton growth. The low temperatures of the environment do not permit rapid growth, which, even under optimal light conditions remains low. In addition, in the euphotic layer, the overall light energy available for algae is considerably reduced due to turbulence, a factor which exacerbates the reduced growth rate.     

Studies on the decolourisation of an artificial textile-effluent by white-rot fungi in N-rich and N-limited media

Coriolopsis gallica and Phanerochaete chrysosporium were selected for their potential ability to degrade five dyes in an artificial effluent. Degradation experiments were carried out in N-rich (C:N ratio 11.6:1) and N-limited (116:1) conditions at an effluent concentration of 100 mg l(-1). P. chrysosporium decolourised 53.6% of the effluent in N-rich conditions and 48% in N-limited conditions. C. gallica decolourised 80.7% in N-rich conditions and 86.9% in N-limited conditions. Nitrogen supplementation improved enzyme activities and dye decolourisation for P. chrysosporium. Additional nitrogen increased enzyme activities for C. gallica but did not improve decolourisation. The results highlight the potential of C. gallica for textile dye degradation.     

Cellular microcystin content in N-limited Microcystis aeruginosa can be predicted from growth rate

Cell quotas of microcystin (Q(MCYST); femtomoles of MCYST per cell), protein, and chlorophyll a (Chl a), cell dry weight, and cell volume were measured over a range of growth rates in N-limited chemostat cultures of the toxic cyanobacterium Microcystis aeruginosa MASH 01-A19. There was a positive linear relationship between Q(MCYST) and specific growth rate (mu), from which we propose a generalized model that enables Q(MCYST) at any nutrient-limited growth rate to be predicted based on a single batch culture experiment. The model predicts Q(MCYST) from mu, mu(max) (maximum specific growth rate), Q(MCYSTmax) (maximum cell quota), and Q(MCYSTmin) (minimum cell quota). Under the conditions examined in this study, we predict a Q(MCYSTmax) of 0.129 fmol cell(-1) at mu(max) and a Q(MCYSTmin) of 0.050 fmol cell(-1) at mu = 0. Net MCYST production rate (R(MCYST)) asymptotes to zero at mu = 0 and reaches a maximum of 0.155 fmol cell(-1) day(-1) at mu(max). MCYST/dry weight ratio (milligrams per gram [dry weight]) increased linearly with mu, whereas the MCYST/protein ratio reached a maximum at intermediate mu. In contrast, the MCYST/Chl a ratio remained constant. Cell volume correlated negatively with mu, leading to an increase in intracellular MCYST concentration at high mu. Taken together, our results show that fast-growing cells of N-limited M. aeruginosa are smaller, are of lower mass, and have a higher intracellular MCYST quota and concentration than slow-growing cells. The data also highlight the importance of determining cell MCYST quotas, as potentially confusing interpretations can arise from determining MCYST content as a ratio to other cell components.     

Studies on the biochemistry and fine structure of silica-shell formation in diatoms

Summary The distribution of radioactivity in ethanol-water-soluble compounds after short periods of photosynthetic incorporation of ¹⁴CO₂ is consistent with the operation of the photosynthetic carbon reduction (PCR) cycle in the fresh water diatom Navicula pelliculosa. Incorporation of ¹⁴CO₂ for extended time periods established the presence of the intermediates of the PCR and tricarboxylic acid (TCA) cycles, amino acids, and organic acids; free sugars were not observed. The main labelled soluble carbohydrate was a glucan. Hydrolysis of the radioactive insoluble material indicated the presence of carbohydrates containing several distinct sugars, and proteins with the usual amino-acid composition. During silicon starvation of exponentially growing cultures, rates of incorporation of both ³²P _i and ¹⁴CO₂ decreased. Incorporation into the lipid increased, with a corresponding decrease into protein and carbohydrate. Reintroduction of Si to staryed cells led to an increased rate of incorporation of both isotopes, and transient changes in the radioactivity in most metabolic intermediates investigated. After 30 min the radioactivity in all PCR cycle intermediates, except phosphoglyceric acid, had increased by about 300%. The radioactivity of citrate and -keto-glutarate increased, whereas that of other TCA-cycle intermediates decreased. An initial decrease in the levels of glutamate, aspartate and glutamine was apparently reversed by cleavage of glutamate-aspartate peptides, as radioactivity of other amino acids increased. Incorporation into the soluble glucan and into protein increased markedly although the rate of incorporation into insoluble carbohydrates remained constant.     

Studies on the biochemistry and fine structure of silica shell formation in diatoms

Summary The sequential wall formation in the centric diatom,Ditylum brightwellii (West) Grunow, is described. The silica deposition vesicle is formed by the coalescence of small vesicles. Silicification of the new valve starts from the central labiate process area prior to the completion of cytokinesis, and the developing valve grows in a centrifugal direction. The initiation of the structures on the valve follows the sequence: labiate process, marginal ridge, and rota. A novel labiate process apparatus, which is situated in the cytoplasm close to the developing labiate process, appears prior to the initiation of the labiate process and disappears upon its maturation. Segments of the girdle bands are formed in individual silica deposition vesicles after the valve matures and is exocytosed. Three morphological forms of deposited silica have been determined: thin base layers, microfibrils, and hexagonal columns. The involvement of cytoplasmic structures in the patterning of the siliceous wall is discussed.     

Studies on the biochemistry and fine structure of silica shell formation in diatoms

Summary Cell division in Navicula pelliculosa (Bréb.) Hilse, strain 668 was synchronized with an alternating regime of 5 h light and 7 h dark. Cell volume and dry weight increased only during the light period. DNA synthesis, which began during the third h of light, was followed sequentially by mitosis, cytokinesis, silicic acid uptake, cell wall formation, and cell separation. Silicification and a small amount of net synthesis of DNA, RNA and protein occurred during the dark at the expense of carbohydrate reserves accumulated during the light period. Cells kept in continuous light, after synchronization with the light-dark regime, remained synchronized through a second division cycle; the sequence of morphological events was the same as that in the light-dark division cycle, but the biosynthesis of macromolecular components changed from a stepwise to a linear pattern. The silicon-starvation synchrony was improved by depriving light-dark synchronized cells of silicic acid at the beginning of their division cycle, then resupplying silicic acid to cells blocked at wall formation.Abbreviation L light - D dark Portions based on a thesis submitted by W.M.D. to the University of California, San Diego in partial fulfillment of the requirements for the PH.D degree     

Studies on the biochemistry and fine structure of silica shell formation in diatoms

Summary The fine structure and pigmentation of an apochlorotic diatom isolated from decaying Macrocystis pyrifera is described. The morphology of acid cleaned shells suggests that the isolate is Nitzschia alba Lewin and Lewin. Light microscope observations indicated a centrally located nucleus and numerous highly refractile bodies which stained differentially with Nile blue and Sudan black B. The stained globules could be correlated in thin-sectioned profiles with either electron dense or lucent areas depending on the fixation technique. In the electron microscope the nucleus, Golgi complex, and mitochondria were similar in appearance to those described for other diatoms. Proplastid-like organelles, delimited by a double membrane, and containing small vesicles were also observed. Neither carotenoids nor chlorophylls could be detected by spectroscopic or spectrofluorometric analysis in vivo or in organic solvent extracts. Deposition of new walls was initiated by formation of silicon deposition-vesicles in the central region of dividing cells. The acentric raphes were deposited last. The genesis and interrelationship of the old plasmalemma, silicalemma, and newly formed plasmalemma are discussed.     

Increase in Si:N drawdown ratio due to resting spore formation by spring bloom-forming diatoms under Fe- and N-limited conditions in the Oyashio region

Resting spore formation and Si:N drawdown ratios were investigated under iron (Fe)- and nitrogen (N)-limited conditions using a unialgal culture of Thalassiosira nordenskioeldii and natural phytoplankton assemblages during the spring bloom in the Oyashio region. In the unialgal culture of T. nordenskioeldii, 20% and 100% of the cells formed resting spores under Fe- and N-limited conditions, respectively. The Si:N drawdown ratios were 2- and 14-fold higher in Fe- and N-limited conditions, respectively, compared to Fe- and N-sufficient conditions. At the start of the natural phytoplankton incubation, 18 among 47 identified diatom species were known resting spore-forming species. Approximately 15 common diatom species formed resting spores under Fe- and N-limited conditions. During the natural phytoplankton incubation, the percentage of the resting spores increased with time under both Fe- and N-limited conditions, reaching 25% and 40% of total diatom abundance, respectively. The Si:N drawdown ratios significantly increased with an increase in the contribution of resting spores in both the unialgal culture and natural phytoplankton incubations. These results suggest that if the bloom dominated by neritic, resting spore-forming diatom species decline by either Fe- or N-depletion, Si may be utilized preferentially to N in the upper mixed layer due to the formation of heavily silicified resting spores.     

Studies on the biochemistry and fine structure of silica shell formation in diatoms

Summary The morphogenesis of the different types of labiate processes is compared among three species of centric diatoms [Stephanopyxis turns (Greville) Ralfs,Odontella sinensis (Greville) Grunow, andOdontella aurita (Lyngbye) Agardh]. In all species, a cytoplasmic structure,i.e., the labiate process apparatus, situated close to the developing labiate process, appears before the labiate process begins to form and disappears upon its maturation. The possibility that the labiate process apparatus is implicated in the phylogeny of the labiate process is discussed.