Johan A. Hellebust

Bio: Johan A. Hellebust is an academic researcher from Woods Hole Oceanographic Institution. The author has contributed to research in topics: Transketolase & Photosynthesis. The author has an hindex of 5, co-authored 5 publications receiving 697 citations.

Excretion of some organic compounds by marine phytoplankton1

Abstract: The excretion of photoassimilated carbon was determined for 22 species of unicellular marine algae in culture during periods of log-phase growth and for some natural marine phytoplankton populations from Vineyard Sound and the Gulf of Maine. Carbon 14 tracers gave some information about the composition of the excreted material. Most of the algae excreted 3-6s of their photoassimilated carbon during logarithmic growth. A few species excreted as much as 10-25s under the same conditions. Algae subjected to two different light intensities, 3,000 lux and 25,000 Iux, varied less than 30% in their relative rates of excretion. However, algae exposed to direct sunlight (lOO,OOO120,000 lux) had very high excretion rates, possibly resulting from damage to the cells by photooxidation. Glycolic acid formed 938% of the total carbon excretion in Olisthodiscus sp., Chaetoceros pelagicus, Chlorococcum sp. and Skeletonema costatum. Lower relative amounts were excreted by most of the species studied. Skeletonema costatum excreted considerably more glycolic acid at light intensities below 15,000 lux than above. This is contrary to the findings of other investigators using the freshwater alga Chlorella pyrenoidosa. The amount of carbon excreted as protein ranged from 0.2 to 5.9%, and that excreted as chloroform-soluble material ranged from 2.8 to 10.3% of the total. After electrodialysis, 12-340/O of the compounds were recovered in the anion fraction. Considerable quantities of amino acids and peptides were also detected as excretory products of many of the algae. A few species excreted a single substance almost exclusively. Thus, Chlorella sp. excreted mainly proline, Dunaliellu tertiolectu mainly glycerol, and Olisthodiscus sp. mainly mannitol. Apparently healthy populations of natural phytoplankton excreted 4-16s of their photoassimilated carbon. However, 17-38s was excreted by a sample taken at the end of a diatom bloom, when a large number of empty frustules was present.

Uptake specificity for organic substrates by the marine diatom melosira nummuloides1

Abstract: SUMMARY Melosira nummuloides, clone Mel-3, shows a very high specificity with regard to its ability to take up organic substrates. Amino acids supplied in the medium at 1 X 10-4 M are taken up at initial rates of the same order of magnitude as that of photoassirnilation of COj. However, sugars, sugar alcohols, or organic acids supplied at the same concentration are not taken up. The mechanism for uptake of amino acids appears to require energy, since tlie uptake of the amino acid analog α-aminoisobutyric acid is strongly inhibited by 2 f-dinitrophenul. The uptake mechanism does not appear to be inducible. The ability of M. numinuloides to utilize amino acids as a nitrogen source is quite restricted. Arginine, ghttamine, asparagine, proline, and glutamic acid were good nitrogen sources. Seventeen other amino acids, including α-aminoisobutyric acid, were unsatisfactory for growth, although they were rapidly taken up from the medium.

Effects of environmental conditions on the rate of photosynthesis and some photosynthetic enzymes in dunaliella tertiolecta butcher1

Abstract: Exponentially growing DunaZieZZa tertiolecta raised under continuous light increased both in photosynthetic capacity and in the activities of two enzymes of the photosynthetic reductive pentose cycle during the first 24 hr after transfer to complete darkness at 18C A rapid decrease in photosynthetic capacity and enzyme activities followed Three days after transfer to darkness, the photosynthetic capacity was only 25% of the initial value, while the corresponding figures for RuDP carboxylase and aldolase activities were 25 and 20% Decline of these metabolic parameters at 18C was greatly delayed by continuous illumination of 20 pw/cm’, an intensity considerably below the compensation point After seven days, the photosynthetic capacity was still 78%, and the RuDP carboxylase and aldolase activities were 65 and 40% of their initial values The same light intensity at a lower temperature (5C) almost entirely eliminated the decrease in photosynthesis and enzyme activities over a 21-day period Changes in RuDP carboxylase activity followed closely those in the rate of photosynthetic dark reactions Parallel changes in the rate of light reactions suggest that the changes in the dark and light systems are interdependent Light quality studies indicate that light absorbed by photosynthetic pigments is primarily responsible for decreasing the rate of loss of photosynthetic capacity and RuDP carboxylase activity It is suggested that light of low intensity, as well as low temperature, may be ecologically important in maintaining the photosynthetic capacity of plankton algae when they are removed from the euphotic zone for a considerable length of time through sinking or vertical mixing

Reductive Pentose Phosphate Cycle in Nitrosocystis oceanus

Abstract: Campbell, Ann E. (Woods Hole Oceanographic Institution, Woods Hole, Mass.), Johan A. Hellebust, and Stanley W. Watson. Reductive pentose phosphate cycle in Nitrosocystis oceanus. J. Bacteriol. 91:1178–1185. 1966.—Assays in cell-free extracts of Nitrosocystis oceanus, a marine chemoautotrophic bacterium, have demonstrated the presence of all of the enzymes of the reductive pentose phosphate cycle, with activities high enough to account for the normal growth rate of the cells. Studies on ribulosediphosphate carboxylase activity in these extracts showed that it is inhibited by MgCl2 (30% at 0.01 m), MnCl2 (70% at 0.01 m), NaCl and KCl (100% at 0.5 m, 63% at 0.2 m), and by sulfate (35% at 0.01 m); phosphate, glutathione, and ethylenediaminetetraacetic acid had no effect. The bacterial enzyme differs from the spinach enzyme with respect to its affinity for bicarbonate and its pH optimum. Whole cells were incubated with C14O2, and the acid-soluble fraction was analyzed by paper chromatography and autoradiography. Phosphoglyceric acid and the sugar phosphates were the earliest labeled compounds; several amino acids and organic acids were also labeled. It is concluded that N. oceanus incorporates CO2 primarily via the reductive pentose phosphate cycle.

The photosynthetic rhythm of acetabularia crenulata. ii. measurements of photoassimilation of carbon dioxide and the activities of enzymes of the reductive pentose cycle

Abstract: 1. The photosynthetic rhythm of Acetabularia crenulata affects both light (quantum yield) and dark reactions in a parallel manner.2. No significant difference was found between the activity of RuDP carboxylase in the extracts of samples taken at the middle of the light and dark periods nor was any difference detected in the affinity of this enzyme to CO2. The activity of RuDP carboxylase in the cell extracts was sufficient to account for the observed rates of photoassimilation of CO2 at saturating light intensities.3. The activities of eight other enzymes of the reductive pentose phosphate cycle were also shown not to differ to a significant extent in extracts of cells taken at the middle of the light and dark periods. Five of these enzymes (phosphoglycerate kinase, glyceraldehyde-3-P dehydrogenase, triose isornerase, R-5-P isomerase and Ru-5-P kinase) had activities considerably above those required for the observed light-saturated rate of CO2 assimilation while the activities of aldolase transketolase a...

Organic geochemistry of natural waters

Abstract: This book is written as a reference on organic substances in natural waters and as a supplementary text for graduate students in water chemistry. The chapters address five topics: amount, origin, nature, geochemistry, and characterization of organic carbon. Of these topics, the main themes are the amount and nature of dissolved organic carbon in natural waters (mainly fresh water, although seawater is briefly discussed). It is hoped that the reader is familiar with organic chemistry, but it is not necessary. The first part of the book is a general overview of the amount and general nature of dissolved organic carbon. Over the past 10 years there has been an exponential increase in knowledge on organic substances in water, which is the result of money directed toward the research of organic compounds, of new methods of analysis (such as gas chromatography and mass spectrometry), and most importantly, the result of more people working in this field. Because of this exponential increase in knowledge, there is a need to pull together and summarize the data that has accumulated from many disciplines over the last decade.

Genetic Engineering of Algae for Enhanced Biofuel Production

Abstract: There are currently intensive global research efforts aimed at increasing and modifying the accumulation of lipids, alcohols, hydrocarbons, polysaccharides, and other energy storage compounds in photosynthetic organisms, yeast, and bacteria through genetic engineering. Many improvements have been realized, including increased lipid and carbohydrate production, improved H2 yields, and the diversion of central metabolic intermediates into fungible biofuels. Photosynthetic microorganisms are attracting considerable interest within these efforts due to their relatively high photosynthetic conversion efficiencies, diverse metabolic capabilities, superior growth rates, and ability to store or secrete energy-rich hydrocarbons. Relative to cyanobacteria, eukaryotic microalgae possess several unique metabolic attributes of relevance to biofuel production, including the accumulation of significant quantities of triacylglycerol; the synthesis of storage starch (amylopectin and amylose), which is similar to that found in higher plants; and the ability to efficiently couple photosynthetic electron transport to H2 production. Although the application of genetic engineering to improve energy production phenotypes in eukaryotic microalgae is in its infancy, significant advances in the development of genetic manipulation tools have recently been achieved with microalgal model systems and are being used to manipulate central carbon metabolism in these organisms. It is likely that many of these advances can be extended to industrially relevant organisms. This review is focused on potential avenues of genetic engineering that may be undertaken in order to improve microalgae as a biofuel platform for the production of biohydrogen, starch-derived alcohols, diesel fuel surrogates, and/or alkanes.

Master recyclers: features and functions of bacteria associated with phytoplankton blooms

Abstract: Marine phytoplankton blooms are annual spring events that are accompanied by a surge in heterotrophic bacteria, primarily roseobacters, flavobacteria and members of the Gammaproteobacteria, which recycle most of the carbon that is fixed by the primary producers. In this Review, Buchan et al. describe the emerging physiological features and functions of these bacterial communities and their interactions with phytoplankton.

Biogeochemistry of Stable Carbon Isotopes

Abstract: In 1947, in his classical paper on the thermodynamic properties of isotopic substances, H. C. Urey [1] laid the foundation of modern isotope geochemistry. At the same time, A. O. Nier [2] designed a new mass spectrometer which allowed the measurement of small differences in isotope abundance ratios. A modification in the Nier-type mass spectrometer and a refinement in instrumentation techniques by McKinney et al. [3] finally initiated stable isotope studies of the type that will be discussed in this review.