The structural nif genes of the cyanobacteria Gloeothece sp. and Calothrix sp. share homology with those of Anabaena sp., but the Gloeothece genes have a different arrangement.

Probes carrying the Anabaena sp. strain PCC 7120 nitrogenase reductase (nifH) and nitrogenase (nifK and nifD) genes were hybridized to Southern blots of DNA from the unicellular, aerobic nitrogen-fixing cyanobacterium Gloeothece sp. strain PCC 6909 and from the filamentous cyanobacterium Calothrix sp. strain PCC 7601. These data suggest that the Gloeothece sp. nif structural proteins must be similar to those of other diazotrophs and that the ability for aerobic nitrogen fixation does not reside in the nif protein complex. We also found that the nif structural genes of Gloeothece sp. are clustered, whereas those of Calothrix sp. are arranged more like those of Anabaena sp.     

Metabolism of glucose by unicellular blue-green algae

Summary A facultative photo- and chemoheterotroph, the unicellular bluegreen alga Aphanocapsa 6714, dissimilates glucose with formation of CO₂ as the only major product. A substantial fraction of the glucose consumed is assimilated and stored as polyglucose (probably glycogen). The oxidation of glucose proceeds through the pentose phosphate pathway. The first enzyme of this pathway, glucose-6-phosphate dehydrogenase, is partly inducible. In addition, the rate of glucose oxidation is controlled, at the level of glucose-6-phosphate dehydrogenase function, by the intracellular level of an intermediate of the Calvin cycle, ribulose-1,5-diphosphate, which is a specific allosteric inhibitor of this enzyme. As a consequence, the rate of glucose oxidation is greatly reduced by illumination, an effect reversed by the presence of DCMU, an inhibitor of photosystem II.Two obligate photoautotrophs, Synechococcus 6301 and Aphanocapsa 6308, produce CO₂ from glucose at extremely low rates, although their levels of pentose pathway enzymes and of hexokinase are similar to those in Aphanocapsa 6714. Failure to grow with glucose appears to reflect the absence of an effective glucose permease. A general hypothesis concerning the primary pathways of carbon metabolism in blue-green algae is presented.Abbreviations A (U)DPG ADP-glucose or UDP-glucose - G-1-P glucose-1-phosphate - G-6-P glucose-6-phosphate - G_(int.) intracellular glucose - F-6-P fructose-6-phosphate - 6-PG 6-phosphogluconate - Ru-5-P ribulose-5-phosphate - RUDP ribulose-1,5-diphosphate - PGA 3-phosphoglycerate - GAP glyceraldehyde-3-phosphate     

Unusual ultrastructural features in three strains of Cyanothece (cyanobacteria)

Three unicellular cyanobacterial strains (PCC 7425, PCC 8303, PCC 9308) assigned to the genus Cyanothece Komárek 1976, which showed an unusually high content of light refractile inclusions when viewed by phase-contrast microscopy, were characterized by confocal laser scanning microscopy and transmission electron microscopy. All strains had concentric cortical thylakoids and a compact central nucleoid. Frequently, the two innermost thylakoid membranes protruded to form circular enclosures containing cytoplasm or electron-transparent granules, or both. The largest granules were partially immersed in the nucleoid region, but they remained attached to the inner cortical thylakoids by a single narrow connection. The pattern of binary cell division in strain PCC 7425 was different than that in strains PCC 8303 and PCC 9308. In the former, all cell wall layers invaginated simultaneously, whereas in the latter the invagination of the outer membrane was delayed compared to that of the cytoplasmic membrane and the peptidoglycan layer. Thus, prior to completion of cell division, the new daughter cells of strains PCC 8303 and PCC 9308 were transiently connected by a thick septum, which was not observed in strain PCC 7425. Nucleoid partitioning coincided with initiation of cell division in all three strains and was unlike that reported in other bacteria and in archaea, in which separation of the nucleoids precedes cell division. Based on the common morphological and ultrastructural features, the three strains of Cyanothece examined constitute a distinct cluster, which might deserve independent generic status.     

Fatty acid composition and physiological properties of some filamentous blue-green algae

Summary The fatty acids of 32 axenic strains of filamentous blue-green algae have been analyzed. As an aid to the interpretation of the results, the strains have been assigned to provisional typological groups based upon their morphology and certain physiological characters. The latter are the ability to grow heterotrophically in the dark with glucose as carbon and energy source, the ability to grow in the light at the expense of glucose in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and the ability to synthesize nitrogenase under anaerobic conditions in the light. Each typological group has been given an appropriate generic name.The strains examined for fatty acid composition can be divided into groups according to the major fatty acid of highest degree of unsaturation found in each strain as was done for the unicellular strains examined previously in this laboratory. Four metabolic groups of strains of unicellular and filamentous blue-green algae can be recognized: 1. those in which there is little or no desaturation of oleate; 2. those in which linoleate is desaturated toward the -end of the molecule to give -linolenate; 3. those in which linoleate is desaturated toward the carboxyl end of the molecule to give -linolenate; 4. those in which octadecatetraenoate is synthesized. The nature of the major cellular fatty acids of two of the strains examined is the same whether growth is in the light or in the dark on glucose. All filamentous strains contain glycolipids with the properties of mono- and digalactosyldiglycerides.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

An axenic cyclostat of Prochlorococcus PCC 9511 with a simulator of natural light regimes

A cyclostat was designed for growing the oceanic oxyphotobacterium Prochlorococcus PCC 9511. Culture of this organism, known to bedifficult to grow, was mastered for a large volume. Prochlorococcusgrew well and axenic conditions were maintained for up to 15 days. Wedesigned an illumination system allowing a smooth bell-shaped irradiancecurve reaching almost 1000 mol quanta m^-2 s^-1 tobe obtained. Cell division was strongly synchronised under theseillumination conditions, which were close to those found at low latitude inthe upper layer of ocean. The described device is particularly well suited tomake experiments requiring up to 6 L per day of well synchronised,exponentially-growing Prochlorococcus culture.     

In situ identification of cyanobacteria with horseradish peroxidase-labeled, rRNA-targeted oligonucleotide probes

Individual cyanobacterial cells are normally identified in environmental samples only on the basis of their pigmentation and morphology. However, these criteria are often insufficient for the differentiation of species. Here, a whole-cell hybridization technique is presented that uses horseradish peroxidase (HRP)-labeled, rRNA-targeted oligonucleotides for in situ identification of cyanobacteria. This indirect method, in which the probe-conferred enzyme has to be visualized in an additional step, was necessary since fluorescently monolabeled oligonucleotides were insufficient to overstain the autofluorescence of the target cells. Initially, a nonfluorescent detection assay was developed and successfully applied to cyanobacterial mats. Later, it was demonstrated that tyramide signal amplification (TSA) resulted in fluorescent signals far above the level of autofluorescence. Furthermore, TSA-based detection of HRP was more sensitive than that based on nonfluorescent substrates. Critical points of the assay, such as cell fixation and permeabilization, specificity, and sensitivity, were systematically investigated by using four oligonucleotides newly designed to target groups of cyanobacteria.     

Heterocyst formation and nitrogenase synthesis in Anabaena sp.

Summary When filaments from a culture of Anabaena sp. growing photoautotrophically with nitrate as a nitrogen source are placed in a nitrate-free mineral medium and incubated anaerobically in the light, the formation of heterocysts and the synthesis of nitrogenase both begin after a lag of about 24 hours. During the lag period, about 70% of the phycocyanin is destroyed. Under an atmosphere of N₂-CO₂, the nitrogenase activity rises to a peak value, and then falls markedly as growth at the expense of N₂ begins. Phycocyanin synthesis resumes concomitantly with growth. Under an atmosphere of Ar-CO₂, the formation of heterocysts and the synthesis of nitrogenase proceed to higher levels than those observed under N₂-CO₂, and the nitrogenase level is thereafter maintained. Under these conditions, neither growth nor resynthesis of phycocyanin occurs, and phycocyanin eventually falls to about 10% of its initial level in the filaments; however, growth can be promptly initiated if N₂ is admitted to the system. The implications of these findings are discussed.     

Halogenase genes in nonribosomal peptide synthetase gene clusters of Microcystis (cyanobacteria): sporadic distribution and evolution

Cyanobacteria of the genus Microcystis are known to produce secondary metabolites of large structural diversity by nonribosomal peptide synthetase (NRPS) pathways. For a number of such compounds, halogenated congeners have been reported along with nonhalogenated ones. In the present study, chlorinated cyanopeptolin- and/or aeruginosin-type peptides were detected by mass spectrometry in 17 out of 28 axenic strains of Microcystis. In these strains, a halogenase gene was identified between 2 genes coding for NRPS modules in respective gene clusters, whereas it was consistently absent when the strains produced only nonchlorinated corresponding congeners. Nucleotide sequences were obtained for 12 complete halogenase genes and 14 intermodule regions of gene clusters lacking a halogenase gene or containing only fragments of it. When a halogenase gene was found absent, a specific, identical excision pattern was observed for both synthetase gene clusters in most strains. A phylogenetic analysis including other bacterial halogenases showed that the NRPS-related halogenases of Microcystis form a monophyletic group divided into 2 subgroups, corresponding to either the cyanopeptolin or the aeruginosin peptide synthetases. The distribution of these peptide synthetase gene clusters, among the tested Microcystis strains, was found in relative agreement with their phylogeny reconstructed from 16S-23S rDNA intergenic spacer sequences, whereas the distribution of the associated halogenase genes appears to be sporadic. The presented data suggest that in cyanobacteria these prevalent halogenase genes originated from an ancient horizontal gene transfer followed by duplication in the cyanobacterial lineage. We propose an evolutionary scenario implying repeated gene losses to explain the distribution of halogenase genes in 2 NRPS gene clusters that subsequently defines the seemingly erratic production of halogenated and nonhalogenated aeruginosins and cyanopeptolins among Microcystis strains.