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Synechocystis trididemni is a photo-oxygenic prokaryotic symbiont in some didemnid ascidians. Although the cells are pink and contain phycoerythrin, they morphologically resemble those of another symbiont of other didemnids, Prochloron didemni, which has no phycobilin pigments but has both chlorophyll a and chlorophyll b. The cytological similarities suggest that they might have evolved from a common ancestor. We examined this hypothesis by comparing nucleotide sequences in gene fragments of the 16S ribosomal RNA (16S rRNA) gene and in the large subunit of Rubisco gene (rbcL). ‘Blast’ search of GenBank showed that the most similar sequences to the 16S rRNA gene and rbcL of S. trididemni were those of Prochloron sp. The percent nucleotide and amino acid identities of the 16S rRNA genes, rbcL and the deduced Rubisco amino acid sequences between Prochloron sp. and S. trididemni were 94%, 90% and 99%, respectively. In trees based on the 16S rRNA gene and rbcL sequences, S. trididemni formed a clade w...

Whereas food has always received much attention in conversation, commerce, and the literature, the subject of feces has been comparatively neglected. To fill this lacuna, a small book on comparative coprology was recently published (Lewin 1999). The present article aims to supplement this book with a review of overlooked or new items relating to biological and medical aspects of coprology, notably chemical and microbial components of human and animal feces, their uses as fertilizers, and a few other sociological impacts.

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 sph...

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.

A large-scale screening program was initiated to evaluate laboratory-cultured blue-green algae (cyanobacteria) as a source of novel compounds with inhibitory activity against certain serine/threonine protein phosphatases. Over 1600 extracts, representing 816 cyanophyte strains with broad habitat and taxonomic diversity, were screened. Inhibitors were identified in extracts produced from all orders tested except Chamaesiphonales, and the family Stigonemataceae was found to contain proportionally more inhibitors as compared to the total screen.

Living cells of the symbiotic prokaryotic alga Prochloran sp. are spherical, tightly inflated by osmotic pressure, and highly refractile. When they die they shrink appreciably, become more translucent, and release a pink exudate with an absorption maximum around 334 nm and a refractive index (RI) considerably above that of seawater. Small samples of such exuded sap were analysed. Estimated by melting-point depression, its osmotic pressure (OP) is about 30% above that of seawater. Glucose and maltose account for much of increase in OP, and proteins (including nucleoproteins) and oligosaccharides for the RI augmentation values observed.

Prochloron (a marine symbiont) and Prochlorothrix (from freshwater plankton) contain chlorophylls a and b; Prochlorococcus (common in marine picoplankton) contains divinyl-chlorophylls a and b. Like cyanophytes they are all clearly photosynthetic prokaryotes, but since they contain no blue or red bilin pigment they were assigned to a new algal sub-class, the Prochlorophyta. However, since their possible phylogenetic relationships to ancestral green-plant chloroplasts have not received support from molecular biology, it now seems expedient to consider them as aberrant cyanophytes.

Lipophilic and hydrophilic extracts from approximately 600 strains of cultured mcyanophytes, 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 agnets.

Prochloron (a marine symbiont) and Prochlorothrix (from freshwater plankton) contain chlorophylls a and b; Prochlorococcus (common in marine picoplankton) contains divinyl-chlorophylls a and b. Like cyanophytes they are all clearly photosynthetic prokaryotes, but since they contain no blue or red bilin pigment they were assigned to a new algal sub-class, the Prochlorophyta. However, since their possible phylogenetic relationships to ancestral green-plant chloroplasts have not received support from molecular biology, it now seems expedient to consider them as aberrant cyanophytes.

Lewin, J. C. (1965) showed that boron is required for the growth of Cylindrotheca fusiformis, and, presumably, other diatoms too. It may be involved in cellular metabolism, as in higher plants, or incorporated by accident or design into the siliceous skeletons (frustules), since B2O3 has been proven to replace SiO2 (e.g. in siliceous rocks). Thus the frustules may contain or bear at their surface a proportion of borosilica, which might reduce their solubility in water. (Incidentally, boron has also been implicated in human bone formation and stability (Newnham, 1994). Deyhle (2002), who determined the content of B in calcareous skeletons of marine foraminifera and compared the isotopic ratios of 11B/10B with that in the environmental sea water, found the B content to be generally less than 10 ppm We sought comparable values for diatom frustules, washed and bleached to remove salts and organic matter, if possible without leaching away any of the B that could be present. We studied fossil diatomite from Lompoc, California; diatomaceous ooze from Myvatn, Iceland; natural plankton diatoms harvested from the sea; and pure cultures of marine and freshwater diatoms grown in the laboratory. By contrast with foraminiferan calcite, our data indicated that diatom frustules contain up to 1,600 ppm of boron, with a more marked enrichment of the lighter isotope. Rough calculations indicate that the B2O3, even if concentrated at the frustule surface, might be enough to reduce the solubility of the frustules. Our B-isotope enrichment data range between +3.9 to −0.2‰, indicating that diatoms preferentially incorporate the light 10B. Such values can provide indications to physico-chemical conditions under which the skeletons were deposited (cf. Lewin, E. et al. 2000) Data will be presented.

Dunaliella: Physiology, Biochemistry and Biotechnology. Edited by M. Avron and A. Ben-Amotz. CRC Press: 1992. Pp. 240. a£109, $149.95.

The Diatoms. Biology and Morphology of the Genera. ByF. E. Round R. M. Crawford and D. G. Mann. Cambridge University Press: 1990. Pp. 747. £125, $250.

Cells of a symbiotic prokaryote, Prochloron sp., in colonies of a tropical ascidian, Lissoclinum punctatum, occur not only outside but also inside cells of the host. Cells of these photosynthetic symbionts of ascidians have previously been reported only extracellularly. The intracellular and extracellular symbionts do not differ morphologically. The host cells carrying the symbionts are freely distributed in the ascidian tunic. They probably endocytize the symbionts and then retain them within a vacuole. Since the intracellular prokaryotes showed no evidence of rejection or degeneration, this association between tunic phagocytes of L. punctatum and cells of Prochloron sp. seems to constitute a stable symrnbiosis, comparable to the postulated ancestral association between heterotrophic cells and the photosynthetic prokaryotes which gave rise to chloroplasts. Additional key words: algae, cyanobacteria, plastid evolution, prochlorophytes, tunicates Chloroplasts are photosynthetic organelles found in all photosynthetic eukaryotes. There is now convincing evidence from molecular biological studies on 16S-rRNA and RNA polymerase subunit (rpo Cl) and ribulose-bisphosphate carboxylase genes (Seewaldt & Stackebrandt 1982; Palenik & Haselkorn 1992; Urbach et al. 1992; Shimada et al. 1995) that these organelles originated from prokaryotic photosynthetic endosymbionts (cyanobacteria) engulfed and retained by heterotrophic host cells (Lewin 1981; Margulis 1981). Symbiotic photosynthetic prokaryotes are therefore of interest in relation to the evolution of chloroplasts. Prochloron is a genus of unicellular prokaryotes with the same chlorophyll pigments, chl a and b, as those in the chloroplasts of green algae and all other green plants (Lewin 1976). Prochlorophyta/Prochlorales was originally established (Lewin 1976, 1977; Florenzano et al. 1986) for prokaryotes that bear chl. a and b, lack bilin pigments, and generate oxygen in photosynthesis; molecular phylogenetic studies, however, indicate that this is a polyphyletic group whose members arose within the cyanobacterial radiation and should be treated as members of Cyanophyta/Cyanobacteria (Palenik & Haselkorn 1992; Urbach et al. 1992; Shimada et al. 1995). Cells of Prochloron occur in coral reef areas, almost exclusively as symbionts of colonial didemnid ascidians (Lewin & Cheng 1989). There the symbionts are normally associated with external or internal colony surfaces, but outside the host cells. Prochloron didemni LEWIN 1977 was originally described from the outer surfaces of didemnid colonies; but since no prochloron cells have been cultured in vitro, and specific distinctions remain to be established, we will refer to the symbionts in this paper simply as Prochloron sp. We present here the first report of Prochloron sp. as an intracellular symbiont in a didemnid ascidian, Lissoclinum punctatum KOTT 1977. Recent molecular biological data (Palenik & Haselkorn 1992; Urbach et al. 1992) indicate that the phylogenetic affinities of chloroplasts are closer to other cyanobacteria than to Prochloron, but we suggest that intracellular Prochloron can be regarded as a model of the ancestral green plastid.