The glbN gene of Nostoc commune UTEX 584 is juxtaposed to nifU and nifH, and it encodes a 12-kDa monomeric hemoglobin that binds oxygen with high affinity. In N. commune UTEX 584, maximum accumulation of GlbN occurred in both the heterocysts and vegetative cells of nitrogen-fixing cultures when the rate of oxygen evolution was repressed to less than 25 mol of O 2 mg of chlorophyll a ؊1 h ؊1 . Accumulation of GlbN coincided with maximum synthesis of NifH and ferredoxin NADP ؉ oxidoreductase (PetH or FNR). A total of 41 strains of cyanobacteria, including 40 nitrogen fixers and representing 16 genera within all five sections of the cyanobacteria were screened for the presence of glbN or GlbN. glbN was present in five Nostoc strains in a single copy. Genomic DNAs from 11 other Nostoc and Anabaena strains, including Anabaena sp. strain PCC 7120, provided no hybridization signals with a glbN probe. A constitutively expressed, 18-kDa protein which cross-reacted strongly with GlbN antibodies was detected in four Anabaena and Nostoc strains and in Trichodesmium thiebautii. The nifU-nifH intergenic region of Nostoc sp. strain MUN 8820 was sequenced (1,229 bp) and was approximately 95% identical to the equivalent region in N. commune UTEX 584. Each strand of the DNA from the nifU-nifH intergenic regions of both strains has the potential to fold into secondary structures in which more than 50% of the bases are internally paired. Mobility shift assays confirmed that NtcA (BifA) bound a site in the nifU-glbN intergenic region of N. commune UTEX 584 approximately 100 bases upstream from the translation initiation site of glbN. This site showed extensive sequence similarity with the promoter region of glnA from Synechococcus sp. strain PCC 7942. In vivo, GlbN had a specific and prominent subcellular location around the periphery of the cytosolic face of the cell membrane, and the protein was found solely in the soluble fraction of cell extracts. Our hypothesis is that GlbN scavenges oxygen for and is a component of a membrane-associated microaerobically induced terminal cytochrome oxidase.
The phycobiliproteins of the unicellular cyanobacterium Synechocystis sp. strain BO 8402 and its derivative strain BO 9201 are compared. The biliproteins of strain BO 8402 are organized in paracrystalline inclusion bodies showing an intense autofluorescence in vivo. These protein-pigment aggregates have been isolated. The highly purified complexes contain phycocyanin with traces of phycoerythrin, corresponding linker polypeptides LR3PC and LR3PE (the latter in a small amount), and a unique colored polypeptide with an Mr of 55,000, designated L55. Allophycocyanin and the core linker polypeptides are absent. The substructure of the aggregates has been studied by electron microscopy. Physiological and genetic implications of the unusual pigment compositions of both strains are discussed.Phycobiliproteins are the major light-harvesting antennae of cyanobacteria and members of the families Rhodophyceae and Cryptophyceae (36,41). In cyanobacteria and members of the Rhodophyceae, they are assembled in phycobilisomeshigh-molecular-weight protein-pigment complexes with Mrs ranging from 5,000,000 to 20,000,000 (20). Phycobilisomes are connected with dimeric or tetrameric photosystem II complexes and localized along with rows of photosystem II particles at the protoplasmic surface of the thylakoid membranes (16,24). They have been characterized in numerous electronmicroscopical (28), spectroscopical (23), biochemical (19-22), genetic (8), and physiological (22, 39, 40) studies. Phycobilisomes consist of a core from which radiate 6 to 10 rods in a specific assembly classified as bundle shaped, hemidiscoidal, or hemiellipsoidal (21,42,44). The rods comprise either only phycocyanin or, in addition, phycoerythrin and, in some cases, phycoerythrocyanin (7), in ratios determined by genetic and environmental parameters (40). The biliproteins are joined by different linker polypeptides LRX that facilitate the sequential assembly and determine the different spectral properties of the subcomplexes (21). The substructure of the rods was postulated to be exclusively hexameric ((X)6 -LRX (19), but recent results indicate a partial assembly of trimeric biliprotein complexes forming hexameric stacks (32). The core is built up by a bi-or tricylindrical central pigment-linker complex, APCM, comprising allophycocyanin and two copies of the anchor polypeptide LCM. It serves as backbone of the phycobilisome and as a structural bridge to photosystem 11 (10,34,35 (33,34). However, the peripheral trimeric allophycocyanin complexes seem not essential for phycobilisome assembly (25,32). Energy is transferred from the outer chromophores of the rods to the terminal acceptors of the allophycocyanin core, allophycocyanin B and LCM (21). Further energy transmission to photosystem II is influenced by environmental factors (30, 40) and state transition processes (4).Synechocystis sp. strain BO 8402 was isolated from the prealpine Lake Constance (12). The strain is characterized by an intense red autofluorescence originating from a localized area within...
Four types of unicellular cyanobacteria were classified by pigment composition and cell size. These originated from the picoplankton fraction of Lake Constance, Germany. β‐Carotene and zeaxanthin were found to be the main carotenoids of three Synechococcus isolates. In this group, coccoid forms with phycocyanin‐rich phycobilisomes also produce caloxanthin and nostoxanthin, which are xanthophylls with 3 and 4 hydroxy groups, respectively. In addition, these rare carotenoids are observed in rod‐forming Synechococcus isolates which contain phycoerythrin‐rich phycobilisomes, but they are very low or absent in the coccoid phycoerythrin‐rich isolates. Due to size and pigment content the coccoid forms are similar to Synechococcus leopoliensis (SAUG B 1402‐1, formerly Anacystis nidulans) and S. rubescens (SAUG B 3.81) while the rod‐forming isolates differ from S. elongatus (PCC 6716) in phycobilisome composition. The isolate BO 8402 was tentatively assigned to Synechocystis but differs in pigment composition from all strains described as yet. The green cultures exhibited a faint red glow due to an unusual high in vivo autofluorescence from phycocyanin. Neither were phycobilisomes found in a standard preparation nor was allophycocyanin present. The most abundant carotenoids are β‐carotene and caloxanthin, while zeaxanthin, with 12 % of all colored carotenoids, is low. All forms described in this paper lack complementary chromatic adaptation, indicating that the pigment composition is a reliable parameter to identify these freshwater isolates.
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