Ralph A. Lewin

Prochlorophyta as a proposed new division of algae

UNICELLULAR algae associated with ascidians from tropical Pacific shores have been reported by various biologists1–5. They are bright green, generally spherical and about 10–20 µm in diameter, and they seem to have no clearly delimited nucleus or plastids. Such cells (identified as Synechocystis didemni), found associated with surfaces of Didemnum colonies on the Pacific coast of Mexico, have been shown by electron microscopy to be prokaryotic6,7, which suggests that they are cyanophytes, that is, blue-green algae. Although all known blue-green algae (other than a few apochlorotic types) contain phycoerythrin, phycocyanin, or both, however, these ascidian symbionts are apple green and contain no detectable bilin pigments. Furthermore, like the eukaryotic algae in the divisions Chlorophyta and Euglenophyta, they contain two chlorophyll components, separable by chromatography and provisionally identifiable as chlorophylls a and b (ref. 8), whereas no cyanophytes are known to contain chlorophyll b. The assignment of S. didemni to any of the established algal divisions, therefore, presents a major taxonomic problem.

Isolation, cultivation and characterization of flexibacteria.

SUMMARY: Eighty-five strains of aerobic microbes capable of gliding on solid substrata have been isolated from samples of marine and freshwater mud and sand collected in various localities around the world. Each strain has been characterized in about 40 tests by a number of morphological, nutritional, physiological and biochemical features.

Observations on Phaeodactylum tricornutum.

SUMMARY: Phaeodactylum tricornutum Bohlin was isolated from a marine tank at Woods Hole, Mass., U.S.A. It appeared to be identical with the Plymouth strain of ‘Nitzschia closterium forma minutissima’. Cells were of two characteristic types, oval and fusiform, each of which remained constant for many cell divisions in clonal culture. Triradiate cells arose rarely as atypical forms of the fusiform variety. Oval cells could arise as endospores within a fusiform cell. The transition from oval to fusiform was also studied, but details of the life cycle remain to be worked out. Electron micrographs showed the fusiform cells to be devoid of any organized siliceous structure, in agreement with previous observations. However, the oval cells were seen to possess a silica valve of a pennate diatom type, resembling those of the genus Cymbella. Only one valve was present on each cell, the remainder of the cell wall being unsilicified. The valve was 6·2μ. long, was equipped with a raphe, and was perforated by pores arranged in 60 striae. Oval and fusiform cells both contained approximately the same amount of silica (0·4–0·5% dry weight). In each case, most of this silica could be recovered as a particulate fraction resistant to digestion in hot nitric acid. The silica obtained from oval cells was in the form of diatom valves, whereas that from fusiform cells consisted of irregular particles clearly not derived from broken silica walls. Mucilaginous capsular material, soluble in hot water, represented 16% of the dry weight of oval cells; it was absent from fusiform cells. Acid hydrolysis and paper chromatography indicated xylose, mannose, fucose, and galactose as components of the capsule.

A Classification of Flexibacteria

SUMMARY: About 90 strains of gliding microbes (flexibacteria) have been considered. Data obtained by Lewin & Lounsbery (1969) and Mandel & Lewin (1969) have been used by Fager (1969) in a computer programme designed to indicate affinities and thereby possible relationships. Largely on the basis of Fagers analysis, a classification of these organisms is here proposed. Including a few species described elsewhere, 27 species and varieties are distinguished, most of them apparently new. A simplified diagnostic key is presented for their identification. They are assigned to six genera, three (Saprospira, Flexithrix and Herpetosiphon) are recognized primarily on morphological grounds; three others (Cytophaga, Flexibacter and Microscilla), here somewhat re-defined, are based largely on other convenient characteristics.

STUDIES ON THE FLAGELLA OF ALGAE. I. GENERAL OBSERVATIONS ON CHLAMYDOMONAS MOEWUSII GERLOFF

1. Cells of Chlamydomonas moewusii normally swim by a synchronized backward beat of the paired flagella.2. When appressed to solid substrata, the flagella are capable of an independent creeping movement. This faculty does not persist in detached flagella.3. During mating, cell clumps are formed by the adhesion of flagella of cells of opposite mating-types.4. By means of the flagella, copulating cells can adjust their relative positions until cytogamy can be initiated.5. Paired cells do not fuse for some hours, during which swimming results from the activity of one partner only.6. By suitable labelling, it can be shown that the flagella of the plus partner remain active, while those of the minus cell cease to beat after pairing.

ANTIVIRAL ACTIVITY OF CULTURED BLUE‐GREEN ALGAE (CYANOPHYTA)1

Lipophilic and hydrophilic extracts from approximately 600 strains of cultured cyanophytes, representing some 300 species, were examined for antiviral activity against three pathogenic viruses. Approximately 10% of the cultures produced substances that caused significant reduction in cytopathic effect normally associated with viral infection. The screening program identified the order Chroococcales as commonly producing antiviral agents.

Prochloron : a microbial enigma

1.Introduction.- 2. Collection and Handling of Prochloron and Its Hosts.- Collection and Handling.- Didemnum molle.- Diplosoma virens.- Diplosoma similis.- Trididemnum cyclops.- Lissoclinum punctatum.- Lissoclinum voeltzkowi.- Lissoclinum patella.- Treatment of Prochloron cells.- Conclusion.- 3. Prochloron in Symbiosis.- Photosynthesis.- Translocation.- Formation of the Symbiosis.- Biochemical Interactions between the Symbionts.- Other Interactions between the Symbionts.- References.- 4. Physiological and Cellular Features of Prochloron.- Photosynthetic Features of Prochloron.- Carbon Metabolism.- Photosynthesis-Irradiance Relationships.- Respiratory Behavior and Carbon Balance in Prochloron.- Properties of the Photosynthetic Pigments and Membranes of Prochloron.- Pigments and Pigment-Protein Complexes.- Why Has Prochloron a Chlorophyll a + b Harvesting System?.- Physiology of the Prochloron-Ascidian Association.- Photosynthesis and Respiration of Symbiotic Didemnids.- Nitrogen Assimilation.- Obligate Nature of Symbiosis.- Some Suggested Physiological Requirements for the Culture of Prochloron.- Conclusion.- References.- 5. Biochemical Features of Prochloron.- General Features of Enzyme Isolation.- Enzymes of Photosynthetic Carbon Metabolism.- Ribulose 1,5-Bisphosphate Carboxylase-Oxygenase.- Phosphoribulose Kinase.- Enzymes of Glucan Synthesis and Storage Carbohydrates.- Lipophilic Components.- Lipid and Sterol Composition.- Pigments.- Properties of Membrane Fractions.- Miscellaneous Compounds and Metabolic Investigations.- Proteins and Amino Acids.- Cell Wall Components.- Nucleic Acids.- Nitrogen Metabolism.- Conclusion.- References.- 6. Phylogenetic Considerations of Prochloron.- Phylogenetic Position.- Phylogentic Rank.- Possible Relationship to Chloroplasts.- References.- 7. The Cytology of Prochloron.- The Cell Wall.- Thylakoids.- Inclusions.- Nucleic Acids.- Conclusion.- References.- 8. A Status Report on Prochlorothrix hollandica a Free-Living Prochlorophyte.- Epilogue.- Author Index.

Growth of post-set oysters, Crassostrea virginica, on high-lipid strains of algal flagellates Tetraselmis spp.

Abstract Nine microalgal strains from the prasinophyte genus Tetraselmis that were chosen for high total lipid content, and one marine strain of the chlorophyte Chlamydomonas , were compared with Isochrysis sp., strain T-ISO, as diets for oyster spat in a controlled laboratory feeding experiment. Five of these high-lipid Tetraselmis strains supported significantly faster oyster growth than an equivalent ration of T-ISO. Doubling times for oyster weight, volume, and shell height were in the range of 1.5–3 weeks on single daily feedings of the best diets. Tetraselmis strains yielding the most rapid oyster growth contained higher contents of the essential fatty acid 20:5 n − 3 and of the sterols 24-methylcholesterol and/or 24-methylenecholesterol. These data are consistent with our earlier findings that these compounds appear to be deficient in most phytoplankton for optimal growth of Crassostrea virginica spat.

Picocystis salinarum gen. et sp. nov. (Chlorophyta) - a new picoplanktonic green alga

Abstract We describe Picocystis salinarum R.A. Lewin, gen. et sp. nov., a hitherto unrecognized kind of green picoplanktonic alga from a saline pond, now isolated in pure culture. The cells are normally spherical or oval, 2–3 μm in diameter, but tend towards a trilobed shape under conditions of nutrient depletion. The ultrastructure is typical for green algae. The pigment complement comprises chlorophylls a and b and the carotenoids neoxanthin, violaxanthin, alloxanthin, monadoxanthin, diatoxanthin, lutein and zeaxanthin. The major component of the cell wall is polyarabinose. Such a unique combination of features suggests that this alga might be assigned to a new lineage within the Chlorophyta.

Culture and Nutrition of Some Apochlorotic Diatoms of the Genus Nitzschia

SUMMARY: Three distinct species of the genus Nitzschia, lacking chloroplasts and therefore obligately heterotrophic, were isolated in pure culture from various marine shores. The organisms reproduced rapidly in a defined medium based on an artificial sea water supplemented with mineral nutrients, thiamine and cobalamin. Lactate or succinate served as sole organic carbon source for all three species; two of the species also used glucose or glutamate. Two of the species were identified as N. putrida Benecke and N. leucosigma Benecke, respectively. The third organism appears to be a new species, here named N. alba.