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The major organic osmoregulatory solutes of 36 cyanobacteria from a wide range of environmental sources have been examined using 3C nuclear magnetic resonance spectre scopy. These strains were also examined for their salt-tolerance, and could be arranged in three salt-tolerance groups, designated freshwater, marine and hypersaline. The most salt-tolerant cyanobacteria in the hypersaline group are properly classified as moderately halophilic. Cyanobacteria from all habitats and taxonomic groups accumulated organic osmoregulatory solutes, and the chemical class of the solute correlated with the salt-tolerance and habitat of the strain. Freshwater strains accumulated simple saccharides, predominantly sucrose and trehalose ; marine strains accumulated the heteroside 0-a-D-glucopyranosyl-( 1 + 2)-glycerol, and hypersaline strains accumulated sucrose and/or trehalose together with glycine betaine or the novel solute L-glutamate betaine (N-trimethyl-L-glutamate) or they accumulated glycine betaine alone. The results suggest that the presence of certain major organic osmoregulatory solutes may be useful in the numerical taxonomy of cyanobacteria, and in the identification of some ionic characteristics of the environment of origin of each isolate.

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Hutt Lagoon, 28" 1 I'S, 1 14" 15'E, 600 km north of Perth, Western Australia and lying 5 m below sea level is the site of a pilot plant erected by Roche Algal Biotechnology for growing and harvesting the alga Dunaliella salina. The lagoon is filled to a depth of 50-75 cm by rainfall (18% w/v salinity or above) during the winter months and is desiccated to a 5 cm or more thick crust during the summer. Salt from the crust used to prepare a growth medium for D. salina introduced a number of protozoa to the cultures, some of which made great inroads on the algal population. Most of the protozoa in the crust are presumed to be in the form of cysts and originate from more or less permanent seeps and pools (>5% w/v salinity) resulting from the inflow of water from the Indian Ocean on the west and from continental ground water on the east. The salt of the crust is thus a mixture of athalassic and thalassic origin. Only the lower reaches of the seeps are inundated by the winter water rise.Fourteen ciliates, 10 zooflagellates and 4 sarcodines were observed frequently enough in brines of over 15% (w/v) salinity to identify. At least one parasite of D. salina is included in the flagellate group. Although no concerted effort with the phytoflagellates was made, the rarely seen species D. peircei, D. jacobae and Ochromonas cosmopolitus were noted, as well as a Gymnodinium sp. The ciliates include the bacteriophagous Trachelocerca conifer, Metacystis truncata, Chilophrya utahensis, Rhopalophrya salina, Uronema marinum, Condylostoma sp. and Palmarella salina. Those eating both bacteria and algae were Nassula sp., Fabrea salina, Blepharisma halophila, Cladotricha sigmoidea, and Euplotes sp. Ciliates feeding on other ciliates include Podophrya sp. and Trematosoma bocqueti. Among the zooflagellates were several species of Monosiga, Rhynchomonas nasuta, Phyllomitus sp., Tetramitus salinus, T. cosmopolitus, Bodo caudatus, B. edax and 3 other distinctive Bodo species, one being parasitic on D. salina. All of the sarcodina fed on both algae and bacteria, except for the smallest amoeba (4 pm diameter rounded) which did not feed on algae, and included Heteramoeba sp. with both flagellate and amoeboid phases, an orange amoeba, an orange filopodforming organism and a colorless filopod-forming organism, the last three of unknown genus.The relationship of these protozoa to the lagoon and to D. salina culturing is discussed.

The effect of sudden salinity increases on the kinetics of growth and carotenogenesis was studied in three geographically diverse isolates of Dunaliella salina. A sudden increase in salinity results in a lag phase in growth and the length of this lag phase is dependent on the final salinity and the magnitude of the salinity change (no lag at 10-15% w/v NaCI, 4-day lag at 30% NaCl). There is also a lag before an increase in the total carotenoid content can be measured following the salinity up-shock, and the length of the lag depends largely on the initial salinity and the magnitude of the salinity up-shock, whereas the rate of carotenogenesis and the final carotenoid content reached depend on the final salinity. The increase in total carotenoid content is mainly due to fl-carotene. Following the salinity up-shock (especially from 10% to 20% NaCl) the proportion of lutein as a percentage of total carotenoids decreases, whereas zeaxanthin increases. This suggests that the pathway synthesising lutein is more sensitive to salt or osmotic stress and is inhibited at higher salinities, thus leading to fl-carotene formation. The proportion of a-carotene does not change.

The process of osmoregulation in a unicellular blue-green alga, Synechococcus sp., has been studied by natural-abundance carbon-13 nuclear magnetic resonance spectroscopy of intact cells and cell extracts. 2-O-alpha-D-Glucopyranosylglycerol was identified as the major organic osmoregulatory solute. This demonstrates the presence of a major osmoregulatory solute in a blue-green alga and is also an example of an osmoregulatory role for glucosylglycerol.

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