Georg Schmetterer

The phototrophic prokaryotes

Historical Perspectives: Research on Purple Bacteria During Twenty-Four Years of International Symposia on Photosynthetic Prokaryotes G. Drews. Freiburg to Vienna-Looking at Cyanobacteria over the Twenty-Five Years N.G. Carr. Photosynthesis: Structural and Functional Analyses of Cyanobacterial Photosystem I: The Directionality of Electron Transfer F. Yang, et al. Electron Transport and Bioenergetics: Photosynthesis and Respiration of Cyanobacteria: Bioenergetic Significance and Molecular Interactions G.A. Peschek. Genome Analysis and Molecular Biology: From Plastid to Cyanobacterial Genomes M. Sugiura. Metabolism of N, C, H: Cyanobacterial Nitrogen Assimilation Genes and NtcA-Dependent Control of Gene Expression E. Flores, et al. Ecology and Symbiosis. Widening Perceptions of the Occurrence and Significance of Cyanobacterial Toxins G.A. Codd, et al. Phylogeny, Taxonomy, and Evolution: Identification of a Putative Gamma Linker Polypeptide Gene in the Marine Oxyphotobacterium Prochlorococcus Marinus: Implications for the Phylogeny of Prochlorococcus Phycoerythrins W.R. Hess, F. Partensky. 86 Additional Articles. Index.

Cytochrome c oxidase genes required for nitrogenase activity and diazotrophic growth in Anabaena sp. PCC 7120

N2 fixation is an O2‐sensitive process and some filamentous diazotrophic cyanobacteria that grow performing oxygenic photosynthesis confine their N2 fixation machinery to heterocysts, specialized cells that maintain a reducing environment adequate for N2 fixation. Respiration is thought to contribute to the diazotrophic metabolism of heterocysts and the genome of the heterocyst‐forming cyanobacterium Anabaena sp. PCC 7120 bears three gene clusters putatively encoding cytochrome c oxidases. Transcript analysis of these cox gene clusters through RNA/DNA hybridization identified two cox operons, cox2 and cox3, that are induced after nitrogen step‐down in an NtcA‐ and HetR‐dependent manner and appear to be expressed specifically in heterocysts. In contrast, cox1 was expressed only in vegetative cells. Expression of cox2 and cox3 occurred at an intermediate stage (about 9 h) during the process of heterocyst development following nitrogen step‐down. Inactivation of genes in the two inducible cox operons, but not separately in either of them, strongly reduced nitrogenase activity and prevented diazotrophic growth in aerobic conditions. These results show that the nitrogen‐regulated cytochrome c oxidase‐type respiratory terminal oxidases Cox2 and Cox3 are essential for heterocyst function in Anabaena sp. PCC 7120.

Evidence for plastoquinol-cytochrome fb-563 reductase as a common electron donor to P700 and cytochrome oxidase in cyanobacteria

Abstract Membranes isolated from Nostoc sp. strain MAC and Anacystis nidulans displayed spectral changes in the cytochrome f b region when examined by reduced minus oxidized or dual wavelength spectrophotometry under physiological conditions. The same changes accompanied both light-induced (photosynthetic) and oxygen-induced (respiratory) electron transport. Physiological reduction of the cytochrome f b moiety was abolished after extraction of plastoquinone but reappeared on reconstitution of the depleted membranes with authentic plastoquinone. Moreover, a mutual inhibition of photosynthetic and respiratory activities could be directly demonstrated with the isolated membranes. From the results it is concluded that the membrane-bound plastoquinol-cytochrome f b reductase functions as a common electron donor to both P700 and the cytochrome oxidase in cyanobacteria.

Do cyanobacteria contain “mammalian-type” cytochrome oxidase?

The cytochrome content of membranes isolated from seven species of cyanobacteria was investigated in terms of conventional difference spectra, carbon monoxide difference spectra, photoaction spectra and photodissociation spectra, and by extraction of acid-labile heme followed by spectral identification. In addition, the effect of various inhibitors and activators on the oxidation of horse heart cytochrome c by the membrane was studied. Both the spectral features and the properties of the cytochrome oxidase reaction catalysed by the membranes suggested the presence of a terminal oxidase strikingly similar to mitochondrial ferrocytochrome c: oxygen oxidoreductase (EC. 1.9.3.1).

Characteristic temperature dependences of respiratory and photosynthetic electron-transport activities in membrane preparations from Anacystis nidulans grown at different temperatures

Abstract Electron-transport activities supported by seven different electron donor/acceptor couples in the light and in the dark, respectively, were measured in particle preparations of the cyanobacterium (blue-green alga) Anacystis nidulans after growth at 40, 30 and 25°C. The Arrhenius plots of the photosynthetic electron-transport reactions between ascorbate (plus 2,6-dichlorophenolindophenol (DCIP)) and NADP + , diphenylcarbazide and DCIP, diaminodurene and benzyl viologen (O 2 ), and the plot of the photooxidation of reduced horse heart cytochrome c showed a single discontinuity at approx. 24–25, 15–17 and 10–13°C in membranes derived from cells grown at 40, 30 and 25°C, respectively. By contrast, the dark respiratory electron-transport reactions between NADPH, ascorbate (plus DCIP) or reduced horse heart cytochrome c and oxygen, and the reduction by horse heart cytochrome c of the aa 3 -type terminal oxidase as followed directly by dual-wavelength spectrophotometry, all gave Arrhenius plots distinguished by two distinct breaks: The break at the higher temperature corresponded to the break also found in the Arrhenius plots of the photosynthetic reactions while an additional discontinuity was observed at 17–18, 8–9 and 5–6°C in membranes prepared from cells grown at 40, 30 and 25°C, respectively. The temperatures at which the discontinuities in the Arrhenius plots occurred depended on the temperature at which the cells had been grown; they were independent, however, of the specific electron donors and acceptors employed. The characteristic features in the Arrhenius plots of respiratory and photosynthetic electron-transport reactions are discussed in terms of lipid-phase transitions in the cytoplasmic and the intracytoplasmic (thylakoid) membranes of A. nidulans . Implications for possibly distinct sites of the respiratory and photosynthetic electron-transport systems in A. nidulans will be mentioned.

Sequence conservation among the glucose transporter from the cyanobacterium Synechocystis sp. PCC 6803 and mammalian glucose transporters

Synechocystis sp. PCC 6803 is capable of facultative photoheterotrophy with glucose as the sole carbon source. Eight mutants that were unable to take up glucose were transformed with plasmids from pooled gene banks of wild-type Synechocystis DNA prepared in an Escherichia coli vector that does not replicate in Synechocystis. One mutant (EG216) could be complemented with all gene banks to restore ability for photoheterotrophic growth. One of the gene banks was fractionated into single clones and plasmid DNA from each clone used to complement EG216. This yielded a 1.5 kb DNA fragment that was sequenced. It contained one complete open reading frame (gtr) whose putative gene product displayed high sequence conservation with the xylose transporter of E. coli and the mammalian glucose transporters. Further, the isolated gtr gene interrupted in vitro by a kanamycin resistance cassette could be used to construct mutants from wild-type Synechocystis sp. PCC 6803 that lacked a functional glucose transporter, thus confirming the identity of the gtr gene with the glucose transporter gene. This is the first prokaryotic glucose transporter known to share a sequence relationship with mammalian glucose transporters and the first sugar transporter from a cyanobacterium characterized at the sequence level.

The coxBAC Operon Encodes a Cytochrome c Oxidase Required for Heterotrophic Growth in the Cyanobacterium Anabaena variabilis Strain ATCC 29413

Three genes, coxB, coxA, and coxC, found in a clone from a gene library of the cyanobacterium Anabaena variabilis strain ATCC 29413, were identified by hybridization with an oligonucleotide specific for aa(3)-type cytochrome c oxidases. Deletion of these genes from the genome of A. variabilis strain ATCC 29413 FD yielded strain CSW1, which displayed no chemoheterotrophic growth and an impaired cytochrome c oxidase activity. Photoautotrophic growth of CSW1, however, was unchanged, even with dinitrogen as the nitrogen source. A higher cytochrome c oxidase activity was detected in membrane preparations from dinitrogen-grown CSW1 than from nitrate-grown CSW1, but comparable activities of respiratory oxygen uptake were found in the wild type and in CSW1. Our data indicate that the identified cox gene cluster is essential for fructose-dependent growth in the dark, but not for growth on dinitrogen, and that other terminal respiratory oxidases are expressed in this cyanobacterium. Transcription analysis showed that coxBAC constitutes an operon which is expressed from two transcriptional start points. The use of one of them was stimulated by fructose.

Deletion of cytochrome c oxidase genes from the cyanobacterium Synechocystis sp. PCC6803: Evidence for alternative respiratory pathways

An oligonucleotide directed against a highly conserved region of aa3-type cytochrome c oxidases was used to clone the cox genes from the cyanobacterium Synechocystis sp. PCC6803. Several overlapping clones were obtained that contained the coxB, coxA, and coxC genes, transcribed in the same direction in that order, coding for subunits II, I, and III, respectively. The deduced protein sequences of the three subunits showed high sequence similarity with the corresponding subunits of all known aa3-type cytochrome c oxidases. A 1.94-kb HindII fragment containing most of coxA and about half of coxC was deleted and replaced by a cassette coding for kanamycin resistance. Mutant cells that were homozygous for the deleted cox locus were obtained. They were viable under photoautotrophic and photoheterotrophic conditions, but contained no cytochrome c oxidase activity. Nevertheless, these mutant cells showed almost normal respiration, defined as cyanide-inhibitable O2 uptake by whole cells in the dark. It is concluded, therefore, that aa3-type cytochrome c oxidase is not the only terminal respiratory oxidase in Synechocystis sp. PCC6803.

Active sodium extrusion reduces net efficiencies of oxidative phosphorylation in the strictly photoautotrophic cyanobacterium Anacystis nidulans

Abstract Efficiencies of oxidative phosphorylation ( P O ratios), intracellular high-energy phosphate pools (ATP and ADP) under aerobic and anaerobic dark conditions, and photosynthetic oxygen evolution measured with intact cells of Anacystis nidulans were found to be specifically depressed by NaCl, but not by KCl. A scheme is proposed which explains the deleterious effect of sodium on the energy metabolism of A. nidulans by competition for protons between ATP synthesis and active sodium extrusion.

Oxidation of exogenous c-type cytochromes by intact spheroplasts of Anacystis nidulans

Intact spheroplasts of the cyanobacterium Anacystis nidulans were found to oxidize reduced c-type cytochromes derived from horse heart, tuna, Saccharomyces oviformis, Candida krusei, Rhodocyclus purpureus, Rhodopseudomonas plustris and Paracoccus denitrificans with characteristics similar to those observed with isolated membranes. Rates of cytochrome c oxidation by the spheroplasts were only 10% of those measured with isolated membranes in which thylakoid-bound cytochrome oxidase contributes to the overall rates. Small amounts of an endogenous c-type cytochrome were released upon lysozyme treatment of the cells. The results appear to indicate the presence of cytochrome oxidase in the cytoplasmic membrane of A. nidulans.