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The metabolic responses of the topshore cyanobacterium (blue-green alga) Rivularia atra (Roth) Born. et Flah. have been studied over the salinity range from 0 to 100% sea water. Photosynthetic competence is maintained throughout, showing only minor variation in response to salinity change. Nitrogenase activity is highest in hyposaline media (5 to 25% sea water), decreasing to approximately 55 to 60% in full-strength sea water. `The principal low molecular weight, ethanol-soluble carbohydrate present within cells of R. atra is the disaccharide trehalose, occurring at concentrations up to 232 mmol kg[sup-1] (cell water) within cells incubated in 100% sea water. Trehalose concentration was found to be dependent upon the salt concentration of the bathing medium, suggesting that it played a role in the maintenance of positive turgor under conditions of varying salinity. Approximately 10 to 12% of the total intracellular trehalose pool was released upon 'downshock' [transfer from 100% sea water to 0% (fresh water)]. Regular release of such quantities of carbohydrate in response to 'downshock', e.g. on exposure to rain or freshwater at low tide, may be locally important in providing fixed carbon for associated heterotrophic organisms, although it represents a negligible input of fixed carbon to the marine littoral environment. [ABSTRACT FROM AUTHOR]

The relationship between ATP and nitrogenase activity has been investigated using the obligate photoautotroph Anabaena cylindrica and Anabaenopsis circularis strain 6720, a photoautotroph which can also use exogenously supplied carbon. In the light photophosphorylation supports maximum observed rates of nitrogenase activity (0.60 and 1.2 μmoles C2H4 mg chl a-1 min-1 under aerobic and microaerobic conditions respectively). The ATP pools sustained under both conditions are similar at 160-200 nmoles mg chl a-1. Oxidative phosphorylation and substrate level phosphorylation are unimportant in supporting nitrogenase activity in the light. Cyclic photophosphorylation can supply all the necessary ATP provided fixed carbon compounds from photosynthetic CO2 fixation (Anabaena) or supplied exogenously (0.2%, w/v, fructose) (Anabaenopsis) are available. When the algae are placed in the dark nitrogenase activity declines. In Anabaenopsis, after an initial rapid drop, nitrogenase activity can be sustained in the presence of exogenous carbohydrate in the dark at up to 70% of the light rate under air, but under anaerobic conditions. This decreased nitrogenase activity in the dark is not due to a lack of nitrogenase synthesis or of penetration of fixed carbon into the cells, but appears to be due to an inherent inability of dark metabolism to generate sufficient ATP and/or reductant for maximum nitrogenase activity. The ATP pool can be sustained at maximum levels when photophosphorylation, cyclic photophosphorylation, and oxidative phosphorylation operate individually, and to a lesser extent when substrate-level phosphorylation operates. No consistent correlations were found between the ATP pool and nitrogenase activity, except under dark anaerobic conditions where there was a positive correlation. [ABSTRACT FROM AUTHOR]

Free-living and symbiotic phycobionts of Anthoceros punctatus and Blasia pusilla reduce acetylene and fix [sup15]N[sub2]; gametophytes and sporophytes without algae do not. Nitrogenase activity by free-living and symbiotic Nostoc is higher under microaerobic than aerobic conditions in the light, and is higher in the light than in the dark. The free-living Blasia phycobiont grows heterotrophically on sucrose and less well on fructose and glucose; heterotrophic growth on galactose is negligible. There is a transfer of [sup15]N from the alga, via the gametophyte to the sporophyte of Anthoceros. About 98% of the extracellular nitrogen liberated into the medium by excised Nostoc colonies is in the form of ammonia; there is negligible liberation of peptides and amino acids. The capacity to excrete ammonia is lost after 72 h of growth free from the liverwort, Excised Nostoc colonies show a negligible capacity to fix CO[sub2] photosynthetically and autoradiographic studies show a transfer of fixed carbon from Blasia gametophytes to the algal cavities. Sucrose may be the main extracellular carbon compound liberated by Blasia gametophytes. In Anthoceros, nitrogenase activity can be sustained for days when alga-containing gametophytes are placed in the dark, if the sporophytes remain exposed to the light. This indicates a transfer of photosynthate from the sporophyte, via the gametophyte, to the alga. [ABSTRACT FROM AUTHOR]

The Anthoceros punctatus-Nostoc and Blasia pusilla-Nostoc symbioses were investigated. In both associations the Nostoc colonies develop in mucilaginous cavities on the undersurface of the gametophyte. The sporophytes of Anthoceros have no Nostoc colonies; no sporophytes of Blasia were found. The symbiotic algae have been identified as Nostoc sphaericum ex. Born et Flah. The heterocyst frequency of the free-living isolates is 3-6% but this increases to 30% (Blasia) and 43% (Anthoceros) when the algae are growing symbiotically. On infecting alga-free gametophytes of Blasia pusillia with Nostoc, algal colonies develop in the cavities within 72 h. The developing Nostoc colonies stretch the cells of the cavity wall and there also arise from a point on the host cavity wall, usually opposite the cavity pore, septate, branched, filamentous protrusions, which increase the surface area of contact between phycobiont and host by about 30% within 4 weeks of colony formation. Such outgrowths may facilitate interchange of metabolites between the alga and liverwort. The Nostoc phycobiont of Anthoceros may infect Blasia and vice-versa, A strain of Nostoc punctiforme isolated from Gunnera also infects Blasia, but four other Nostoc isolates, including one from cycad root nodules, do not. Five other heterocystous algae, five non-heterocystous filamentous algae and one unicellular alga tested do not infect Blasia. The nitrogen contents of thalli with Nostoc colonies are significantly higher than those treated with algae which do not develop colonies. The symbiotic algae differ physiologically and biochemically from free-living algae. They show higher rates of nitrogenase activity (acetylene reduction assay), are depleted of nitrogen-storing phycobilin pigments and structured granules and although metabolically active do not evolve O[sub2] or fix CO[sub2] photosynthetically, but do have polyhedral bodies which contain the key CO[sub2]-fixing enzyme ribulose-1,5-diphosphate carboxylase. [ABSTRACT FROM AUTHOR]

Bacterium CP-1 isolated from Scottish waters is an aerobic prokaryote with a high guanine:cytosine ratio (68%), which causes lysis of a variety of blue-green algae. When suspensions of algae and bacteria are mixed the bacteria can be seen to glide towards the algae where they become attached end-on round the algal cells. There is evidence that the bacteria produce substances at the point of contact with the algae which are necessary for algal lysis to occur. Lysis of vegetative cells may occur within 30 minutes of the bacteria becoming attached. Heterocysts do not lyse in this way although their intracellular contents may eventually degenerate. When vegetative cells rupture, the protoplasmic contents, including gas vacuoles when present, are released and empty-looking 'ghosts' which retain the original cell shape may remain for a time although these too eventually break down. There is some evidence that the mode of filament lysis may be random, intercalary or terminal. At the ultrastructural level the initial effect of CP-1 is to cause lysis of the L[SUB2] layer of the algal cell wall and this effect is similar to that obtained using lysozyme. This is followed by rupture or disintegration of the other cell wall layers, and 'scroll' -like structures, either of coiled up cell wall material (Microcystis) or of the plasmalemma (Nostoc) may be found scattered throughout the preparations of lysed cells. In fully lysed cells there is a loss of polyphosphate bodies, structured granules, gas vacuoles, and most other cellular inclusions. Released gas vesicles can be collected from the surface of the solution of lysed cells, and there is evidence that these vesicles may fracture easily near the conical ends. In fully lysed cells, the thylakoid membranes remain, often with wide lumens between. This thylakoidal system is contorted and branched, ramifies through the cell and shows constrictions of the membrane system at intervals. [ABSTRACT FROM AUTHOR]

Of thirty-six species of metabolically active lichens taken mainly from Scottish coastal habitats, eight showed a capacity to reduce acetylene to ethylene. These were species of Collema Web., Lichina C. Ag., Peltigera Willd. and Placopsis Nyl. and all contained a blue-green alga as the primary or secondary phycobiont. Acetylene reduction rates were sometimes high in the field and showed marked diurnal and seasonal variations. Nitrogenase activity was higher in vegetative than in fruiting thalli of Peltigera rufescens, and in P. canina was higher nearer the apices of the thalli than in older parts. Of the environmental factors affecting fixation, desiccation was the most important, temperature was less important and the lichens, while requiring light, could continue to fix nitrogen in the dark for up to i8 hours (Lichina confinis) and 26 hours (Peltigera rufescens). The average percentage nitrogen contents of nitrogen-fixing lichens (2.20%) was significantly higher than the non-nitrogen-fixing lichens (0.83%). The maximum and mean fates of nitrogen fixation by P. rufescens were 38.1 and 4.1 μg N (mg N)[SUP-1] day[SUP-1] respectively. The corresponding values for Lichina confinis were 29.4 and 0.4. [ABSTRACT FROM AUTHOR]

Four bacterial isolates have been obtained which cause lysis of laboratory cultures and natural populations of blue-green algae. Over forty algal strains belonging to all orders of the blue-green algae and including bloom-forming species are susceptible. The bacteria also lyse certain gram-positive and gram-negative bacteria. The organisms are aerobic, gram-negative rods, aflagellate, motile and pigmented with an absorption maximum of the pigments in methanol occurring at nm and with shoulders at 460 nm and 415 nm. The guanine and cytosine in the DNA is within the range of 65-69±1 M%. The organisms are identified tentatively as members of the Myxobacterales. Lysis of vegetative cells of the algae depends on the presence of growing bacteria, bacteria-free filtrates alone being insufficient to cause lysis. Heterocysts are not lysed. The bacterial plaques resemble viral plaques in appearance. The lytic agents rapidly inhibit metabolic activity of the susceptible algae and may cause cell lysis within 2-10 hours. The isolates can be propagated readily in the absence of the host and are probably widely distributed in freshwater habitats. [ABSTRACT FROM AUTHOR]

Nitrogen fixation in various Wisconsin lakes was compared using the C[sub2]H[sub2] reduction technique. Rates of C[sub2]H[sub2] reduction were unaffected by N[sub2] when sufficient C[sub2]H[sub2] was added to the gas phase. Thus in field studies the natural gas phase need not be removed before the addition of C[sub2]H[sub2]. C[sub2]H[sub2] was reduced rapidly in eutrophic waters (Little Arbor Vitae Lake, Lake Mendota and southern Green Bay) but more slowly in oligotrophic waters (Crystal Lake, Trout Lake, Lake Mary and northern Green Bay). C[sub2]H[sub2] reduction was greatest in the surface waters, was largely light-dependent and showed a marked diurnal variation. There was also significant variation with area and with time, and in general acetylene reduction was detected only when heterocystous algae were present. The rate of nitrogen fixation in Lake Mendota, calculated on the basis of weekly measurements taken during most of the ice-free season, was approximately 2.4 kg/ha/year. [ABSTRACT FROM AUTHOR]

The effects of temperature and salinity on the carbohydrate accumulation profiles of a range of unicellular cyanobacteria (blue-green algae) have been studied. Four isolates of Synechocystis sp. which usually accumulated glucosyl-glycerol produced a second carbohydrate, sucrose, when grown in a seawater-based medium at high temperature (35 °C). In contrast, three sucrose-accumulating isolates of Synechococcus, grown over a range of temperatures and salinities, did not produce a second detectable low molecular weight carbohydrate in any experimental treatment. The interaction of temperature and salinity was further examined in Synechocystis PCC 6714. Sucrose production was found to be favoured by high temperature and low salinity. The rate and extent of sucrose accumulation differed in cells grown at 20 and 37 °C reaching an upper asymptote 12 h after upshock at 37 °C and 24 h after upshock at 20 °C followed by a decrease to ah approximately constant level after 96 h. This is the first demonstration of the accumulation of sucrose as a second osmotically active carbohydrate in cyanobacteria. [ABSTRACT FROM AUTHOR]

The lichen Peltigera aphthosa consists of a green alga Coccomyxa, a fungus, and a N2-fixing Nostoc which is located in superficial packets (cephalodia). In symbiosis the Nostoc shows only low activities of glutamine synthetase, but the cephalodia show very high activities of glutamate dehydrogenase. Alanine dehydrogenase activity is rather similar in all components. The Nostoc liberates over 95% of the N2 which it fixes as NH4+, and fungal glutamate dehydrogenase in the cephalodia appears to be important in the assimilation of this NH4+. Exogenous NH4+(5 mM) has no effect on acetylene reduction activity by excised cephalodia but completely inhibits acetylene reduction by cephalodia attached to lichen discs (of fungus + Coccomyxa) within 24 h. This inhibition can be overcome by inhibiting main thallus glutamine synthetase activity by adding the glutamate analogue, L-methionine-SR-sulphoximine (MSX). On adding exogenous NH4+ to main thallus discs with cephalodia, glutamine accumulates in the cephalodia when main thallus glutamine synthetase is active but not when it is inactivated by MSX. Exogenous glutamine also specifically inhibits nitrogenase activity by the cephalodia although exogenous alanine and glutamate (all 5 mM) have no such effect. The data indicate that glutamine produced in the main thallus may be involved in the regulation of nitrogenase activity by the cephalodial Nostoc. [ABSTRACT FROM AUTHOR]

On adding NH4+ to nitrogen-fixing cultures of A nabaena cylindrica, the glutamine pool of the intact filament increases within seconds. Nitrogenase activity and then glutamine synthetase activity decline. There are no changes in the activities of glutamate-aspartate aminotransferase, or in the pools of alanine, glycine and aspartate during this period. Nitrogenase activity is usually inversely related to the size of the glutamine pool and shows little correlation with glutamine synthetase activity per se. There is no evidence of adenylylation or deadenylylation of glutamine synthetase (snake venom phosphodiesterase has no effect on activity, there is no serological homogeneity with the Escherichia coli enzyme which shows a covalent modification; the ratio of biosynthetic : transferase activity does not change markedly on the addition of NH4+ and the kinetics of decrease in glutamine synthetase activity are not consistent with adenylylation of the enzyme). Feed-back inhibition occurs, with alanine and glycine being particularly effective inhibitors and with some inhibition occurring with AMP, carbamoyl phosphate and aspartate. Histidine, lysine, ornithine, citrulline and arginine were non-inhibitory at the concentrations used. There is no evidence of inhibition of glutamine synthetase by glutamine. The addition of azaserine inhibits glutamine uptake by intact filaments and reduces the subsequent conversion of glutamine to glutamate within the filament by 77%. Such results are consistent with the operation of the glutamine synthetase--glutamate synthase pathway in A nabaena cylindrica. [ABSTRACT FROM AUTHOR]

A virus which is pathogenic to certain blue-green algae belonging to the genera Plectonema, Phormidium and Lyngbya has been isolated from a variety of freshwater habitats in Scotland and has been detected over a 12-month period in one of these habitats. The virus (D-1) is a cyanophage, has an isohedral head and a short tail and is morphologically and serologically related to the LPP-1 virus isolated from the United States and the G111 virus isolated from Israel by other workers. The partially purified virus has an absorption spectrum characteristic of a nucleoprotein with a maximum at 260 nm and a minimum at 243 nm. D-1 is temperature sensitive being inactivated on heating at 60° C for 6 minutes. Its multiplication rate is fast, increasing from an initial titre of 10[SUP3] to 10[SUP12]PFU/ml within 40 hours. The lysis of the host cell results in a rapid loss of the phycobilin and chlorophyll pigments. [ABSTRACT FROM AUTHOR]