Excitation energy transfer in Anacystis nidulans.

Several natural acyclic sesquiterpenes with capacity for insect growth regulation have been shown to uncouple oxidative phosphorylation in mouse-liver mitochondria. These agents stimulate succinate oxidation, reverse oligomycin-inhibited state 3 respiration, activate ATP-hydrolysis, induce loss of respiratory control and abolish $\text{ADP}\text{O}$ ratio. Permeability of the inner membrane to potassium, sodium, ammonium and chloride ions as well as to protons is also enhanced. Since the structure of these agents precludes protonophoric activity, the possible mechanism of uncoupling by these juvenile hormones is discussed.     

Light Harvesting in Anacystis nidulans Studied in Pigment Mutants

Spontaneous pigment mutants of Anacystis nidulans were self-selected for improved growth in far red light (> 650 nanometers). Questions were asked about those features of the light-harvesting mechanism which altered to give the mutants improved photosynthetic performance in far red. Answers were sought by comparing pigment and reaction center concentrations for the parent and six mutants grown in gold fluorescent and in far red light. Three significant results emerged. The ratio of reaction centers for photoreactions I and II (RC1/RC2) varied by a value of about 2.1 for all clones grown in gold and a value of about 1.1 for all clones grown in far red. Alteration of the ratio was not evident in any of the mutants.     

Coupling of Solar Energy to Hydrogen Peroxide Production in the Cyanobacterium Anacystis nidulans

Hydrogen peroxide production by blue-green algae (cyanobacteria) under photoautotrophic conditions is of great interest as a model system for the bioconversion of solar energy. Our experimental system was based on the photosynthetic reduction of molecular oxygen with electrons from water by Anacystis nidulans 1402-1 as the biophotocatalyst and methyl viologen as a redox intermediate. It has been demonstrated that the metabolic conditions of the algae in their different growth stages strongly influence the capacity for hydrogen peroxide photoproduction, and so the initial formation rate and net peroxide yield became maximum in the mid-log phase of growth. The overall process can be optimized in the presence of certain metabolic inhibitors such as iodoacetamide and p-hydroxymercuribenzoate, as well as by permeabilization of the cellular membrane after drastic temperature changes and by immobilization of the cells in inert supports such as agar and alginate.     

Distribution of Chlorophyll between the Two Photoreactions in Photosynthesis of the Blue-Green Alga Anacystis nidulans Grown at Two Different Light Intensities

Anacystis nidulans was grown in white light of two different intensities, 7 and 50 W ·m^?2. The in vivo pigmentations of the two cultures were compared. The ratio phycocyanin/chlorophyll a was 0.96 for cells grown at 7 W · m^?2 and 0.37 for cells grown at 50 W · m^?2. Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared, using French press treatment and fractionated centrifugation. Algae grown in the irradiance of 50 W · m^?2 showed a chlorophyll a/P700 ratio of 260, while algae grown at 7 W · m^?2 had a value of 140. Corresponding PSI-particles showed values of 122 and 109 respectively. Light-induced absorption difference spectra measured between 400–450nm indicated different ratios between cytochrome f and P700 in the two algal cultures. Enhancement studies of photosynthetic oxygen evolution were carried out. When a background beam of 691 nm was superimposed upon a signal beam of 625 nm, good enhancement was observed for both cultures. With the wavelengths 675 and 691 nm together a pronounced enhancement could be detected only in algae grown at the higher light level. Absorption spectra recorded on whole cells at 77°K revealed a small shift of the main red chlorophyll a absorption peak caused by light intensity. It is proposed that the reduction of the phycocyanin/chlorophyll a ratio in high light-grown cells is accompanied by an increased energy distribution by chlorophyll a into PSII.     

Changes in Pigment Composition and Photosynthesis Induced by Iron-Deficiency in the Blue-Green Alga Anacystis nidulans

Absorption spectra and photosynthetic action spectra have been determined for living Anacystis grown in complete and iron-deficient inorganic media. The absorption studies have shown a spectral shift from 679 nm to 673 nm in the chlorophyll a absorption peak when the algae had to grow without iron. The shift is believed to reflect a changed ratio between at least two chlorophyll a forms denoted Ca670 and Ca680 in this work. Action spectra determinations have revealed a similar shift from 677 nm to 672 nm in the photosynthetic activity peak of chlorophyll a when Anacystis was transferred to a medium without iron. It is proposed that both Ca670 and Ca680 participate in light absorption for photo-system I.     

Phycobilisomes in Spheroplasts of Anacystis nidulans

Phycobilisomes in Anacystis nidulans can be seen more readily in spheroplasts than in cells with intact walls.     

Nitrate transport in the cyanobacterium Anacystis nidulans

A significant progress in the knowledge of different aspects of nitrate transport in the unicellular cyanobacterium Anacystis (Synechococcus ) has been achieved in the last few years. The main contributions of our group are summarized in this article and discussed in relation to other information available. Endergonic accumulation of nitrate into the cells, indicative of the operation of an active nitrate transport system, has been experimentally substantiated and methods established to evaluate and analyze the activity of the system. Nitrate transport activity is sensitive to regulation exerted by products of both ammonium and CO₂ assimilation, thus providing evidence that photosynthetic nitrate assimilation in cyanobacteria is primarily controlled at the level of substrate supply to the cell. The expression of nitrate transport was also shown to be under nitrogen control, being repressed when ammonium is used as the nitrogen source. A 47-kDa polypeptide, which is a major plasma membrane component in nitrate-grown cells but is virtually absent in ammonium-grown cells, was identified as an essential component of the nitrate transporter. More recently, evidence of a strict Na'-dependence of active nitrate transport has been obtained, Δμ(Na⁺) appearing as the driving force of a sodium-nitrate symport system. Kinetic studies indicate also that the nitrate transporter may transport nitrite into the cell.     

Light-Induced Changes in Pigment Composition of Photosynthetic Lamellae and Cell-Free Extracts from the Blue-Green Alga Anacystis nidulans

Anacystis nidulans was grown at two different levels of white light, 7 and50 W^.m^?2. The cells were disrupted through French press treatment, and phycocyanin-free photosynthetic lamellae were obtained from the homogenate by fractionated centrifugation. Comparative absorption studies of the lamellae revealed that high intensity gave an increased carotenoid content relative to chlorophyll a. The spectral characteristics of the cell-free supernatants were also analysed. The high light intensity gave increased contents of both pteridines (410 nm) and allophycocyanin (655 nm) compared with the contents in algae grown at the low light level.     

The Susceptibility of Photosynthesis to Photoinhibition and the Capacity of Recovery in High and Low Light Grown Cyanobacteria, Anacystis nidulans

The susceptibility of photosynthesis to photoinhibition and the rate of its recovery were studied in the cyanobacterium Anacystis nidulans grown at a low (10 micromoles per square meter per second) and a high (120 micromoles per square meter per second) photosynthetically active radiation. The rate of light limited photosynthetic O₂ evolution was measured to determine levels of photoinhibition and rates of recovery. Studies of photoinhibition and recovery with and without the translation inhibitor streptomycin demonstrated the importance of a recovery process for the susceptibility of photosynthesis to photoinhibition. We concluded that the approximately 3 times lower susceptibility to photoinhibition of high light than of low light grown cells, significantly depended on high light grown cells having an approximately 3 times higher recovery capacity than low light grown cells. It is suggested that these differences in susceptibility to photoinhibition and recovery depends on high light grown cells having a higher turnover rate of photosystem II protein(s) that is(are) the primary site(s) of photodamage, than have low light grown cells. Furthermore, we demonstrated that photoinhibition of A. nidulans may occur under physiological light conditions without visible harm to the growth of the cell culture. The results give support for the hypotheses that the net photoinhibitory damage of photosystem II results from the balance between the photoinhibitory process and the operation of a recovery process; the capacity of the latter determining significant differences in the susceptibility of photosynthesis to photoinhibition of high and low light grown A. nidulans.     

The biosynthesis of phycocyanobilin in Anacystis nidulans

Aminolevulinic acid, the common precursor of linear and cyclic tetrapyrroles, can arise either by condensation of succinate and glycine or from the ent     

Characterization of Sulphate Uptake in Anacystis nidulans

Sulphate uptake in the blue-green alga Anacystis nidulans appears based upon an active mechanism with a Km of 0.75 μM and V_max of 0.7 pmol/min × 10⁶ cells. Sulphate uptake is competitively inhibited by thiosulphate and sulphite. The sulphate uptake has a pH optimum at 8 and a temperature optimum at 40°C. By increasing the extracellular sulphate concentration from 0.1 to 10 μM the sulphate pool in Anacystis was altered from 8.3, 10^?5M to 5.9, 10^?4M.     

Labeling the deoxyribonucleic acid of Anacystis nidulans.

Analysis of cell-free extracts of Anacystis nidulans disclosed the absence of both thymidine phosphorylase (EC 2.4.2.4) and thymidine kinase (EC 2.7.1.21) activities. Thymine and thymidine were incorporated inefficiently by intact cells of A. nidulans either in the presence or absence of deoxyguanosine (250 mug/ml). Deoxythymidine monophosphate incorporation was also inefficient. Radioactive deoxyadenosine, at a minimally toxic level (3 mug/ml), was incorporated effectively into the deoxyribonucleic acid (DNA). A cesium chloride-ethidium bromide gradient analysis of the DNA revealed that both the plasmid DNA and the principal DNA of the A. nidulans genome were labeled effectively in cells exposed to [8-14C]deoxyadenosine.     

Regulated nitrate transport in the cyanobacterium Anacystis nidulans.

Intracellular accumulation of nitrate, indicative of the operation of an active nitrate transport system, has been measured in intact cells of the cyanobacterium Anacystis nidulans. The ability of the cells to accumulate nitrate was effectively hindered by either ammonium addition or selective inhibition of CO2 fixation by DL-glyceraldehyde, with the effect of either compound being prevented by previously blocking ammonium assimilation. The results support the contention that nitrate utilization in cyanobacteria is regulated at the level of nitrate transport through the concerted action of ammonium assimilation and CO2 fixation.     

Proton pump coupled to cytochrome c oxidase in the cyanobacterium Anacystis nidulans

Intact spheroplasts of the cyanobacterium Anacystis nidulans were found to oxidize various exogenous c-type cytochromes with concomitant proton extrusion. In the coupled state, H+/e stoichiometries close to 1 were measured, regardless of absolute reaction rates. It is concluded that the proton translocation observed is an intrinsic property of the cytoplasmic membrane-bound cytochrome c oxidase of A. nidulans.     

Leucine biosynthesis in the blue-green bacterium Anacystis nidulans.

Leucine-requiring auxotrophs of the unicellular blue-green bacterium Anacystis nidulans have been isolated. Extracts of these mutants were deficient in alpha-isopropylmalate synthetase (EC 4.1.3.12). In wild-type cells, this enzyme was subject to feedback inhibition by leucine. However, formation of the enzymes of leucine biosynthesis was little affected by exogenous leucine in either wild-type or mutant strains. Cultures of the latter subjected to extreme leucine deprivation showed no change in specific activity of beta-isopropylmalate isomerase (EC 4.2.1.33) and at most a 50% increase in the specific activity of beta-isopropylmalate dehydrogenase (EC 1.1.1.85). These results are compared with others bearing on the evolution of the control of amino acid biosynthesis in blue-green bacteria.     

Growth response of Anacystis nidulans to sodium and phosphate availability

The growth response of Anacystis nidulans to sodium and phosphate was studied in batch culture under controlled laboratory conditions. Sodium (range=0–10 mg/l) significantly enhanced growth, most notably, after sodium and phosphate starvation. The magnitude of the increase in growth was dependent on the initial cell density, external concentrations of phosphate, sodium, and potassium, and the nutritional status of the algal inoculum. The increase in ambient sodium levels in many lakes may provide a competitive advantage to some blue-green algae.