Evidences showing ultraviolet-B radiation-induced damage of DNA in cyanobacteria and its detection by PCR assay

Impact of ultraviolet-B radiation in causing the damages to the DNA of the cyanobacterium, Anabaena strain BT2 has been investigated. Exposure of genomic DNA (in vitro) to UV-B radiation for 1 h did not cause any shift in the absorption peak (lambda(max)) but more than 30% increase in absorbance was noticed in comparison to untreated control DNA (no exposure to UV-B). This increase in absorbance in a way may be comparable to typical hypochromic effect but there was no decrease in absorbance following transfer of UV-B-treated DNA to fluorescent light or in the dark. That the damaging effect of UV-B radiation on native structure of DNA is indeed real was also evident from the PCR-based assay such as RAPD, rDNA amplification, and ARDRA. Template activity of UV-B-treated genomic DNA was drastically inhibited, there was no amplification in RAPD assay after prior exposure of DNA to UV-B for 60 min. Only one band of approximately 400 bp was observed even after 60 min of exposure which suggests that certain segment of DNA strand is resistant to UV-B effects. Similar to the effects on RAPD profile, amplification of rDNA was significantly inhibited following exposure of genomic DNA to UV-B. Our findings clearly demonstrate that UV-B does affect the DNA of cyanobacteria and the killings of these microbes might be due to the irreversible damages caused to DNA by this high energy radiation. It is felt that PCR assay may be conveniently used for screening the damages caused to DNA by UV-B radiation in cyanobacteria and other microorganisms.

Physiology ofAnabaena khannae andChlorococcum humicola under fluoride stress

Sodium fluoride showed pH-dependent physiological responses in the two test microalgae Anabaena khannae and Chlorococcum humicola. A. khannae showed severe membrane damage with fluoride at low pH with leakage of pigments and electrolytes. Annihilation of photosynthesis along with inhibition in 14C uptake was observed at pH 6 with 50 mg/L fluoride. While respiration was less affected in the cyanobacterium, C. humicola showed 30 % inhibition in respiratory activity. Resistance of C. humicola to fluoride toxicity has been attributed to the hindrance provided by the thick cell envelope, intracellular compartmentation and increase in extracellular pH as a consequence of its metabolism.

Molybdate transport and its effect on nitrogen utilization in the cyanobacterium Anabaena variabilis ATCC 29413

Molybdenum is an essential component of the cofactors of many metalloenzymes including nitrate reductase and Mo-nitrogenase. The cyanobacterium Anabaena variabilis ATCC 29413 uses nitrate and atmospheric N2 as sources of nitrogen for growth. Two of the three nitrogenases in this strain are Mo-dependent enzymes, as is nitrate reductase; thus, transport of molybdate is important for growth of this strain. High-affinity transport of molybdate in A. variabilis was mediated by an ABC-type transport system encoded by the products of modA and modBC. The modBC gene comprised a fused orf including components corresponding to modB and modC of Escherichia coli. The deduced ModC part of the fused gene lacked a recognizable molybdate-binding domain. Expression of modA and modBC was induced by starvation for molybdate. Mutants in modA or modBC were unable to grow using nitrate or Mo-nitrogenase. Growth using the alternative V-nitrogenase was not impaired in the mutants. A high concentration of molybdate (10 microM) supported normal growth of the modBC mutant using the Nif1 Mo-nitrogenase, indicating that there was a low-affinity molybdate transport system in this strain. The modBC mutant did not detectably transport low concentrations of 99Mo (molybdate), but did transport high concentrations. However, such transport was observed only after cells were starved for sulphate, suggesting that an inducible sulphate transport system might also serve as a low-affinity molybdate transport system in this strain.

Methods for in situ detection and characterization of extracellular polymers in biofilms by electron microscopy

Electron microscopy of biofilms and the localization of extracellular polymers at high resolution require the adaptation of conventional electron microscopic preparation and imaging techniques. A method developed for in situ fixation and embedding of biofilms, imaging of unstained thick sections with electron spectroscopic imaging and the application of lectin or antibody-based marker systems allowed interpretation of extracellular polymer distribution at micrometer scale. By this way, it is possible to discriminate in situ between extracellular polymers produced by different organisms.

Heterocyst development in Anabaena

Many filamentous nitrogen-fixing cyanobacteria protect nitrogenase from oxygen in differentiated cells called heterocysts. Heterocyst development is controlled by the availability of nitrogen compounds in the environment and by intrinsic factors that regulate the frequency and pattern of heterocysts along vegetative cell filaments. Recent progress in understanding heterocyst development in these simple multicellular organisms includes demonstrating the role of 2-oxoglutarate in regulating the activity of the transcription factor NtcA, the identification of additional genes in the regulatory network, such as hetF, and the further characterization of previously identified genes and proteins, including DevR/HepK, hetR, hetN, patS and patB.

Reductive transformation of methyl parathion by the cyanobacterium Anabaena sp. strain PCC7120

Organophosphorus compounds are toxic chemicals that are applied worldwide as household pesticides and for crop protection, and they are stockpiled for chemical warfare. As a result, they are routinely detected in air and water. Methods and routes of biodegradation of these compounds are being sought. We report that under aerobic, photosynthetic conditions, the cyanobacterium Anabaena sp. transformed methyl parathion first to o,o-dimethyl o-p-nitrosophenyl thiophosphate and then to o,o-dimethyl o-p-aminophenyl thiophosphate by reducing the nitro group. The process of methyl parathion transformation occurred in the light, but not in the dark. Methyl parathion was toxic to cyanobacteria in the dark but did not affect their viability in the light. Methyl parathion transformation was not affected by mutations in the genes involved in nitrate reduction in cyanobacteria.

An increase in the level of 2-oxoglutarate promotes heterocyst development in the cyanobacterium Anabaena sp. strain PCC 7120

In the filamentous cyanobacterium Anabaena sp. strain PCC 7120, a starvation of combined nitrogen induces differentiation of heterocysts, cells specialized in nitrogen fixation. How do filaments perceive the limitation of the source of combined nitrogen, and what determines the proportion of heterocysts? In cyanobacteria, 2-oxoglutarate provides a carbon skeleton for the incorporation of inorganic nitrogen. Recently, it has been proposed that the concentration of 2-oxoglutarate reflects the nitrogen status in cyanobacteria. To investigate the effect of 2-oxoglutarate on heterocyst development, a heterologous gene encoding a 2-oxoglutarate permease under the control of a regulated promoter was expressed in Anabaena sp. PCC 7120. The increase of 2-oxoglutarate within cells can trigger heterocyst differentiation in a subpopulation of filaments even in the presence of nitrate. In the absence of a source of combined nitrogen, it can increase heterocyst frequency, advance the timing of commitment to heterocyst development and further increase the proportion of heterocysts in a patS mutant. Here, it is proposed that the intracellular concentration of 2-oxoglutarate is involved in the determination of the proportion of the two cell types according to the carbon/nitrogen status of the filament.

Anabaena sp. strain PCC 7120 hetY gene influences heterocyst development

The filamentous cyanobacterium Anabaena (Nostoc) sp. strain PCC 7120 responds to starvation for fixed nitrogen by producing a semiregular pattern of nitrogen-fixing cells called heterocysts. Overexpression of the hetY gene partially suppressed heterocyst formation, resulting in an abnormal heterocyst pattern. Inactivation of hetY increased the time required for heterocyst maturation and caused defects in heterocyst morphology. The 489-bp hetY gene (alr2300), which is adjacent to patS (asl2301), encodes a protein that belongs to a conserved family of bacterial hypothetical proteins that contain an ATP-binding motif.

Effects of lindane on the photosynthetic apparatus of the cyanobacterium Anabaena: fluorescence induction studies and immunolocalization of ferredoxin-NADP+ reductase

INTENTION, GOAL, SCOPE, BACKGROUND

Cyanobacteria have the natural ability to degrade moderate amounts of organic pollutants. However, when pollutant concentration exceeds the level of tolerance, bleaching of the cells and death occur within 24 hours. Under stress conditions, cyanobacterial response includes the short-term adaptation of the photosynthetic apparatus to light quality, named state transitions. Moreover, prolonged stresses produce changes in the functional organization of phycobilisomes and in the core-complexes of both photosystems, which can result in large changes in the PS II fluorescence yield. The localization of ferredoxin-NADP+ reductase (FNR) at the ends of some peripheral rods of the cyanobacterial phycobilisomes, makes this protein a useful marker to check phycobilisome integrity.

OBJECTIVE

The goal of this work is to improve the knowledge of the mechanism of action of a very potent pesticide, lindane (gamma-hexaclorociclohexane), in the cyanobacterium Anabaena sp., which can be considered a potential candidate for bioremediation of pesticides. We have studied the effect of lindane on the photosynthetic apparatus of Anabaena using fluorescence induction studies. As ferredoxin-NADP+ reductase plays a key role in the response to oxidative stress in several systems, changes in synthesis, degradation and activity of FNR were analyzed. Immunolocalization of this enzyme was used as a marker of phycobilisome integrity. The knowledge of the changes caused by lindane in the photosynthetic apparatus is essential for rational further design of genetically-modified cyanobacteria with improved biorremediation abilities.

METHODS

Polyphasic chlorophyll a fluorescence rise measurements (OJIP) have been used to evaluate the vitality and stress adaptation of the nitrogen-fixing cyanobacterium Anabaena PCC 7119 in the presence of increasing concentrations of lindane. Effects of the pesticide on the ultrastructure have been investigated by electron microscopy, and FNR has been used as a marker of phycobilisome integrity.

RESULTS AND DISCUSSION

Cultures of Anabaena sp. treated with moderate amounts of lindane showed a decrease in growth rate followed by a recovery after 72 hours of pesticide treatment. Concentrations of lindane below 5 ppm increased the photosynthetic performance and activity of the cells. Higher amounts of pesticide caused a decrease in these activities which seems to be due to a non-competitive inhibition of PS II. Active PS II units are converted into non-QA reducing, so called heat sink centers. Specific activity and amount of FNR in lindane-treated cells were similar to the values measured in control cultures. Release of FNR from the thylakoid after 48 hours of exposure to 5 ppm of lindane towards the cytoplasm was detected by immunogold labeling and electron microscopy.

CONCLUSIONS

From these results, we conclude that the photosynthetic performance and activity of the cells are slightly increased in the presence of lindane up to 5 ppm. Moreover, in those conditions, lindane did not produce significant changes in the synthesis, degradation or activity of FNR. The high capability of Anabaena to tolerate lindane makes this cyanobacterium a good candidate for phytoremediation of polluted areas.

RECOMMENDATION AND OUTLOOK

The results of this study show that cultures of Anabaena PCC 7119 tolerate lindane up to 5 ppm, without significant changes in the photosynthetic vitality index of the cells. However, a slight increase in phycobiliprotein synthesis is observed, which is related to total protein content. This change might be due to degradation of proteins less stable than phycobiliproteins. An identification of the proteins with altered expression pattern in the presence of the pesticide remains the subject of further work and will provide valuable information for the preparation of strains which are highly tolerant to lindane.

Role of white light in reversing UV-B-mediated effects in the N2-fixing cyanobacterium Anabaena BT2

The effects of various irradiances of artificial UV-B (280-315 nm) in the presence or absence of visible light (photosynthetically active radiation) on growth, survival, 14CO2 uptake and ribulose 1,5-bisphosphate carboxylase (RuBISCO) activity were studied in the N2-fixing cyanobacterium Anabaena BT2. We tested the hypothesis whether or not visible radiation offers any protection against UV-B-induced deleterious effects on growth and photosynthesis in Anabaena BT2. Attempts were also made to determine the irradiances of UV-B where inhibitory effects could be mitigated by simultaneous irradiation with visible light. Exposure of cultures to 0.2 W m(-2) or higher irradiance of UV-B caused inhibition of growth and survival and growth ceased above 1.0 W m(-2). 14CO uptake and RuBISCO activity were found to be more sensitive to UV-B and around 60% reduction in 14CO2 uptake and RuBISCO activity occurred after exposure of cultures to 0.4 W m(-2) for 1 h. However, growth, 14CO2 uptake and RuBISCO activity were nearly normal when UV-B (0.4 W m(-2)) and visible light (14.4 W m(-2)) were given simultaneously. Blue radiation (450 nm) was found to be the most effective in photoreactivation against UV-B, better than UV-A or any other light wavelength band. Our results demonstrate that the studied cyanobacterium possesses active photoreactivation mechanism(s) against UV-B-mediated damage which in turn probably allow survival under natural conditions in spite of being continuously exposed to the UV-B component present in the solar radiation. Continued growth of many algae and cyanobacteria in the presence of intense solar UV-B radiation under natural conditions seems to be due to the active role of photoreactivation.

Conserved temperature-dependent expression of RNA-binding proteins in cyanobacteria with different temperature optima

The expression of the rbp genes, which encode small RNA-binding proteins with a single RNA-recognition motif, is known to increase at low temperature in Anabaena variabilis M3. The 5'-untranslated region (UTR) of the rbpA1 gene is involved in the cold-regulation. We compared the regulation of the rbp genes in three strains of cyanobacteria having different temperature optima, namely, a mesophilic strain Anabaena sp. PCC 7120, a thermophilic strain Thermosynechococcus elongatus BP-1, and a psychrophilic Antarctic strain Oscillatoria sp. SU1. In Anabaena 7120 and T. elongatus, all the rbp gene sequences are known, and the 5'-UTR sequences of some rbp genes have a high similarity to the 5'-UTR of rbpA1. We found that transcripts as well as protein products of these rbp genes accumulated at low temperature. In addition, the expression of rbp genes increased at low temperature in the Oscillatoria sp. SU1. This suggests that a mechanism of cold-regulation of rbp genes is common among various species of cyanobacteria that belong to different taxa and have different temperature optima.

PlmA, a new member of the GntR family, has plasmid maintenance functions in Anabaena sp. strain PCC 7120

The filamentous cyanobacterium Anabaena (Nostoc) sp. strain PCC 7120 maintains a genome that is divided into a 6.4-Mb chromosome, three large plasmids of more that 100 kb, two medium-sized plasmids of 55 and 40 kb, and a 5.5-kb plasmid. Plasmid copy number can be dynamic in some cyanobacterial species, and the genes that regulate this process have not been characterized. Here we show that mutations in an open reading frame, all1076, reduce the numbers of copies per chromosome of several plasmids. In a mutant strain, plasmids pCC7120delta and pCC7120zeta are both reduced to less than 50% of their wild-type levels. The exogenous pDU1-based plasmid pAM1691 is reduced to less than 25% of its wild-type level, and the plasmid is rapidly lost. The peptide encoded by all1076 shows similarity to members of the GntR family of transcriptional regulators. Phylogenetic analysis reveals a new domain topology within the GntR family. PlmA homologs, all coming from cyanobacterial species, form a new subfamily that is distinct from the previously identified subfamilies. The all1076 locus, named plmA, regulates plasmid maintenance functions in Anabaena sp. strain PCC 7120.

Description of five mutants of the cyanobacterium Anabaena sp strain PCC 7120 affected in heterocyst differentiation and identification of the transposon-tagged genes

When growing on N(2) as sole nitrogen source, the filamentous cyanobacterium Anabaena sp. PCC 7120 forms N(2) fixing heterocysts in a semi-regular pattern. To identify genes involved in heterocyst differentiation we characterised five transposon-generated mutants that were not able to form mature heterocysts. After recovering the transposon together with the flanking region of the Anabaena chromosome the affected genes were identified. Four of the genes could be involved in formation of the heterocyst-specific envelope: alr2887, encoding a probable outer membrane efflux protein, alr3698, a glycosyl transferase, all4388, a putative periplasmic polysaccharide export protein and alr5357, the formerly described gene hglB/hetM, encoding a fatty-acid synthetase. Another gene, all0049/mutS2, may be important in one of the genome rearrangements that occur during heterocyst differentiation. By transcriptional fusion to reporter genes luxAB differential expression of alr2887, alr3698 and alr5357 could be monitored during heterocyst differentiation.

Selective control of cyanobacteria by surfactin-containing culture broth of Bacillus subtilis C1

Of several types of chemical surfactants and biosurfactants, only the culture broth of Bacillus subtilis C1 containing surfactin at 10 mg l(-1) completely inhibited the growth of Microcystis aeruginosa, a bloom-forming cyanobacterium in highly eutrophic lakes. The broth with 10 mg surfactin l(-1) also removed 85% of the maximally grown M. aeruginosa (chlorophyll-a concentration, 1000 microg l(-1)) within 2 d, and the removal efficiency was enhanced by Ca2+ over 1 mM. The growth of Anabaena affinis, another bloom-forming cyanobacterium, was also inhibited about 70% with surfactin at 10 mg l(-1) broth. However, the effect of the broth was delayed over 3 d in the green algae, Chlorella vulgaris and Scenedesmus sp., and was negligible in a diatom, Navicula sp., indicating the potential for the selective control of cyanobacterial blooms.

Genome-wide expression analysis of the responses to nitrogen deprivation in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120

A heterocyst is a terminally differentiated cell of cyanobacteria which is specialized in dinitrogen fixation. Heterocyst differentiation in Anabaena sp. strain PCC 7120 is triggered by deprivation of combined nitrogen in the medium. Although various genes that are upregulated during heterocyst differentiation have been reported, most studies to date were limited to individual or a small number of genes. We prepared microarrays in collaboration with other members of the Anabaena Genome Project. Here we report on the genome-wide expression analysis of the responses to nitrogen deprivation in Anabaena. Many unidentified genes, as well as previously known genes, were found to be upregulated by nitrogen deprivation at various time points. Three main profiles of gene expression were found: genes expressed transiently at an early stage (1-3 hr) of nitrogen deprivation, genes expressed transiently at a later stage (8 hr), and genes expressed when heterocysts are formed (24 hr). We also noted that many of the upregulated genes were physically clustered to form 'expressed islands' on the chromosome. Namely, large, continuous genomic regions containing many genes were upregulated in a coordinated manner. This suggests a mechanism of global regulation of gene expression that involves chromosomal structure, which is reminiscent of eukaryotic chromatin remodelling. The possible implications of this global regulation are discussed.

Effects of intense PAR and UV radiation on photosynthesis, growth and pigmentation in the rice-field cyanobacterium Anabaena sp

The relative importance of photosynthetically active radiation and UV on photoinhibition has been studied in the cyanobacterium Anabaena sp. by measuring the effective quantum yield, growth, pigmentation and fluorescence emission.

Heat-shock response and its contribution to thermotolerance of the nitrogen-fixing cyanobacterium Anabaena sp. strain L-31

Compared to Escherichia coli, the nitrogen-fixing soil cyanobacterium Anabaena sp. strain L-31 exhibited significantly superior abilities to survive prolonged and continuous heat stress and recover therefrom. Temperature upshift induced the synthesis of heat-shock proteins of similar molecular mass in the two microbes. However, in Anabaena sp. strain L-31 the heat-shock proteins (particularly the GroEL proteins) were synthesised throughout the stress period, were much more stable and accumulated during heat stress. In contrast, in E. coli the heat-shock proteins were transiently synthesised, quickly turned over and did not accumulate. Nitrogenase activity of Anabaena cells of sp. strain L-31 continuously exposed to heat stress for 7 days rapidly recovered from thermal injury, although growth recovery was delayed. Exposure of E. coli cells to >4.5 h of heat stress resulted in a complete loss of viability and the ability to recover. Marked differences in the synthesis, stability and accumulation of heat-shock proteins appear to distinguish these bacteria in their thermotolerance and recovery from heat stress.

Inactivation of cyanobacterial nitrogenase after exposure to ultraviolet-B radiation

Exposure of the N(2)-fixing cyanobacterium Anabaena BT2 to ultraviolet-B radiation (2.5 W m(-2)) for 30 min resulted in complete loss of nitrogenase activity but 100% cell killing occurred only after a 90-min exposure. Inactivation of nitrogenase activity was not specific to Anabaena BT2; other species also showed a similar effect. The time required for 100% killing and inactivation of nitrogenase activity differed in various species, and this difference may be ascribed to the presence of different levels of UV-B protection mechanisms in individual species. Inhibition of nitrogenase activity was immediate, since exposure of cultures to UV-B for as little as 5 min elicited some inhibition of activity. The activity of UV-B-inhibited nitrogenase did not recover upon transfer of exposed cells to fluorescent light, suggesting that the inhibition may be due to specific inactivation of the enzyme. By employment of inhibitors of protein synthesis and PS-II activity, it was demonstrated that restoration of nitrogenase activity in a UV-B-treated culture occurred by fresh synthesis of nitrogenase polypeptide. Our findings suggest that estimation of nitrogenase activity in diazotrophic species may be used as a marker enzyme for assessing the impact of UV-B radiation.

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.

Biotransformation of an organochlorine insecticide, endosulfan, by Anabaena species

This study assesses the role of the blue-green algal species present in the soil in the dissipation of endosulfan and its metabolites in the soil environment. Two Anabaena species, Anabaena sp. PCC 7120 and Anabaena flos-aquae, were used in this study. Anabaena sp. PCC 7120 produced three principal biotransformation compounds, chiefly endosulfan diol (endodiol), and minor amounts of endosulfan hydroxyether and endosulfan lactone. Trace amounts of endosulfan sulfate were detected. In comparison, the biotransformation of endosulfan by Anabaena flos-aquae yielded mainly endodiol with minor amounts of endosulfan sulfate. An unknown compound was produced up to 70% from endosulfan spiked in the medium inoculated by A. flos-aquae after 8 days of incubation. Therefore, the endosulfan fate was dependent on the species. Within 1 day of incubation, two Anabaena species produced low amounts of beta-endosulfan after application of alpha-endosulfan. These results suggest the presence of isomerase in the Anabaena species. Further studies using a fermentor to control the medium pH at 7.2 to minimize chemical hydrolysis of endosulfan revealed a major production of endodiol with minor amounts of endosulfan sulfate and the unknown compound. These results showed that the production of the unknown compound might be dependent on the alkaline pH in the medium and that the production of endodiol by A. flos-aquae might be biologically controlled. This study showed that two algal species could contribute in the detoxification pathways of endosulfan in the soil environment.

Hydrogen production by cyanobacteria in an automated outdoor photobioreactor under aerobic conditions

The possibility of hydrogen production by a hydrogenase impaired mutant strain of Anabaena variabilis in outdoor culture was studied. A computer-controlled rooftop (outdoor) tubular photobioreactor (4.35 L) was assembled. H(2) production rates by A. variabilis PK84 grown in CO(2) + air in the photobioreactor were measured together with other parameters such as temperature, irradiance, pH, dry biomass weight, and pO(2), and Chl a concentrations during summer months of 1998 and 1999. Efficiencies of light energy bioconversion to H(2) energy and energy accumulated in biomass were calculated. The influence of irradiance, temperature, and mode of cultivation on H(2) production and efficiency of light energy bioconversion were evaluated. The culture produced up to 1.1 L H(2) day(-1) PhBR(-1). The efficiency of light energy to H(2) energy bioconversion on some days was 0.094%. However, the conditions for maximum H(2) photoproduction and for maximum efficiency of light energy to H(2) energy bioconversion were not the same. A. variabilis PK84 could produce hydrogen for prolonged periods (up to 40 days) without injection of fresh inoculum. During this period photobioreactor produced 24.5 L of H(2). Possibilities for increasing the efficiency of light energy conversion are discussed.

hetL overexpression stimulates heterocyst formation in Anabaena sp. strain PCC 7120

The cyanobacterium Anabaena sp. strain PCC 7120 forms single heterocysts about every 10 to 15 vegetative cells along filaments. PatS is thought to be a peptide intercellular signal made by developing heterocysts that prevents neighboring cells from differentiating. Overexpression of the patS gene suppresses heterocyst formation. The hetL gene (all3740) was isolated in a genetic screen to identify genes involved in PatS signaling. Extracopy hetL allowed heterocyst formation in a patS overexpression strain. hetL overexpression from a heterologous promoter in wild-type Anabaena PCC 7120 induced multiple-contiguous heterocysts (Mch) in nitrate-containing medium. The predicted HetL protein is composed almost entirely of pentapeptide repeats with a consensus of A(D/N)L*X, where * is a polar amino acid. Thirty Anabaena PCC 7120 genes contain this repeat motif. A synthetic pentapeptide corresponding to the last 5 amino acids of PatS, which suppresses heterocyst formation in the wild type, did not suppress heterocyst formation in a hetL overexpression strain, indicating that HetL overexpression is affecting heterocyst regulation downstream of PatS production. The transcription regulator NtcA is required for the initiation of heterocyst formation. hetL overexpression allowed the initiation of heterocyst development in an ntcA-null mutant, but differentiation was incomplete. hetR and hetC mutations that block heterocyst development are epistatic to hetL overexpression. A hetL-null mutant showed normal heterocyst development and diazotrophic growth, which could indicate that it is not normally involved in regulating development, that it normally plays a nonessential accessory role, or perhaps that its loss is compensated by cross talk or redundancy with other pentapeptide repeat proteins.

Isolation and characterization of mutants of two diazotrophic cyanobacteria tolerant to high concentrations of inorganic carbon

Diazotrophic heterocystous cyanobacteria Nostoc calcicola and Anabaena sp. ARM 629 were investigated for their ability to grow in presence of sodium bicarbonate (NaHCO3) or carbon dioxide (CO2) under cultural conditions. Maximum growth was observed in 75 mM NaHCO3 and 5% CO2 in N. calcicola and Anabaena ARM 629, respectively. Although their growth rate declined, N. calcicola and Anabaena sp. could tolerate upto 250 mM NaHCO3 and 20% CO2, respectively. N-methyl-N'-nitro N nitrosoguanidine induced mutants of these cyanobacteria were isolated which showed growth upto 1 M NaHCO3 (N. calcicola) or 50% CO2 (Anabaena sp.) in comparison to their wild types. The mutants also showed cross-resistance to either of the inorganic carbon compounds, which was not observed for wild type. It was concluded that mutants were altered in multiple properties enabling them to grow at elevated levels of inorganic carbon compounds.

Differential expression and localization of Mn and Fe superoxide dismutases in the heterocystous cyanobacterium Anabaena sp. strain PCC 7120

Superoxide dismutases (Sods) play very important roles in preventing oxidative damages in aerobic organisms. The nitrogen-fixing heterocystous cyanobacterium Anabaena sp. strain PCC 7120 has two Sod-encoding genes: a sodB, encoding a soluble iron-containing Sod (FeSod), and a sodA, encoding a manganese-containing Sod (MnSod). The FeSod was purified and characterized. A recombinant FeSod was also obtained by overproduction in Escherichia coli. Immunoblot study of the FeSod during induction of heterocyst differentiation showed that the cells produced six- to eightfold more FeSod 8 h after a shift from a nitrogen-replete condition to a nitrogen-depleted condition. However, the amount of FeSod protein in filaments with mature heterocysts was the same as that in filaments grown with combined nitrogen. Superoxide anion-generating chemicals such as methyl viologen did not induce upregulation of the sodB gene expression. The predicted preprotein of the sodA gene has a leader peptide and a motif for membrane attachment at the N terminus of the mature protein. Activity staining after gel electrophoresis of the purified thylakoid membranes showed that most of the MnSod in Anabaena sp. strain PCC 7120 was located on thylakoids toward the lumenal side. Expression of the sodA gene in E. coli shows that the leader peptide was required for its activity and the membrane localization of the MnSod. Northern hybridization detected one 0.82-kb transcript of sodA. The sodA gene was upregulated by methyl viologen, whereas its amount was unchanged during heterocyst differentiation. Immunoblotting and activity staining showed that isolated heterocysts contained a lower but still significant amount of FeSod, suggesting that its function is required in heterocysts. No MnSod was observed in isolated heterocysts. These results show that the two different Sod proteins have differentiated roles in Anabaena sp. strain PCC 7120.

Impact of four pesticides on the growth and metabolic activities of two photosynthetic algae

The acute toxicity was determined for soil algae Chlorella kesslerei and Anabaena inaequalis, exposed to pesticides lindane, pentachlorophenol (PCP), isoproturon (IPU), and methyl parathion (MP). Toxicity markers included growth inhibition, chlorophyll biosynthesis, and total carbohydrate content, as a function of dose and time. Concentration response functions (EC50) were estimated by probit data transformation and weighted linear regression analyses. Lindane's toxicity to Chlorella increased sharply with time (EC50 = 7490, 10.3, 0.09 mg L(-1); 24, 48, 72 h), but remained nearly constant through 72 h with Anabaena (8.7-6.7 mg L(-1); 24-72 h). PCP at low concentrations stimulated algal growth and chlorophyll a production, an effect reversed at higher doses. Anabaena was less tolerant of PCP and MP than was Chlorella. The 96-h static EC50 values for Chlorella were: 0.003, 34, 0.05, and 291 mg L(-1) for lindane, PCP, isoproturon, and MP, respectively; for Anabaena, these were 4.2, 0.13, 0.21, and 19 mg L(-1). Carbohydrate production responses were similar to those of cell density (growth) and chlorophyll biosynthesis, with MP having the lowest adverse impact. The overall relative toxicity among the four tested pesticides was: for Chlorella, lindane > IPU >> PCP >> MP; and for Anabaena, PCP > IPU > lindane > MP. The results confirm that toxicants such as these pesticides may affect individual (though related) species to significantly different degrees.

Characterization of salinity-tolerant mutant of Anabaena doliolum exhibiting multiple stress tolerance

Results show that an isolated mutant of the cyanobacterium Anabaena doliolum is a fast-growing strain. It exhibits approximately twofold higher NaCl tolerance than the wild type. It also reveals cross-resistance against the herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), drug bacitracin, and LiCl. Further, an improved LiCl tolerance property of both the mutant and wild-type strains at high concentration of NaCl (40 m M) may be interpreted in terms of competitive inhibition of the Li(+) uptake by Na(+) ions, whereas bacitracin resistance in these organisms is described to be the result of an alteration in the drug transporting channels of membrane. The multiple stress tolerance property of the A. doliolum may be attributed to altered membrane characteristics in the mutant strain, leading to reduced intake of such toxicants.

Involvement of the hap gene (mucinase) in the survival of Vibrio cholerae O1 in association with the blue-green alga, Anabaena sp

Mucinase is a soluble haemagglutinin protease, which may be important for the survival of Vibrio cholerae in association with mucilaginous blue-green algae (cyanobacteria). A comparative survival study was carried out with an Anabaena sp. and a wild-type V. cholerae O1 strain hap+ gene (haemagglutinin-protease), together with its isogenic mutant hap (hap-deleted gene). A simple spread plate technique was followed to count culturable V. cholerae O1 on taurocholate tellurite gelatin agar plate. The fluorescent antibody technique of Kogure et al. (1979) was used for the microscopical viable count of V. cholerae O1. Polymerase chain reaction (PCR) and Southern blot hybridization were carried out to detect a lower number of viable but nonculturable (VBNC) V. cholerae O1 from the laboratory-based experiments. The wild and mutant V. cholerae O1 strains survived in culturable form for 22 and 10 days. respectively, in association with the Anabaena sp., with the difference being statistically significant (P < 0.01). The fluorescent antibody technique, PCR, and hybridization results also showed that the wild strain survived better in the VBNC state than did the mutant VBNC strain in association with an Anabaena sp. These results indicate that the enzyme mucinase may play an important role in the association and long-term survival of V. cholerae O1 with a mucilaginous blue-green alga, Anabaena sp.

Cellular fatty acids as chemotaxonomic markers of the genera Anabaena, Aphanizomenon, Microcystis, Nostoc and Planktothrix (cyanobacteria)

The cellular fatty acid content of 22 cyanobacterial strains belonging to the genera Anabaena, Aphanizomenon, Calothrix, Cylindrospermum, Nostoc, Microcystis and Planktothrix were analysed. The identities of the major peaks were confirmed by MS. Correspondence analysis of the data revealed three distinct groups formed by the Microcystis strains, the Nostoc/Planktothrix strains and the Anabaena/Aphanizomenon/Cylindrospermum strains. The Calothrix strain did not cluster with the other heterocystous cyanobacteria, supporting its morphological classification separate from the Nostocaceae family. The presence of large amounts of the fatty acids 18:30omega6,9,12c and 18:0 iso distinguished the Microcystis strains from the other cyanobacteria studied. The high content of 16:1omega7c grouped the Nostoc strains with the Planktothrix strains. A free-living strain of Nostoc contained 16:1omegao5c and 16: 1omega7c (about 1: 1), separating it from the symbiotic Nostoc strain and the Planktothrix strains. the strains of Anabaena, Aphanizomenon and Cylindrospermum grouped tightly and were characterized by the presence of 16:1omega9c and 16:0 anteiso fatty acids. Correspondence analysis of Anabaena, Aphanizomenon and Cylindrospermum showed that all hepatotoxic Anabaena strains grouped together, whereas the non-toxic and neurotoxic Anabaena strains grouped with the non-toxic Aphanizomenon strains.

Physiological and biochemical alterations in Anabaena 7120 under iron stress

Various physiological and biochemical process like growth, NO3- -uptake, nitrate reductase, glutamine synthetase and ATPases (Mg2+ and Ca2+ dependent) in the cyanobacterium Anabaena 7120 were observed under iron stress. Growth was found to be maximum in 50 microM Fe3+ added cells however, 20 microM Fe3+ (the Fe3+ concentration generally used for routine culturing of cyanobacterial cell in Chu 10 medium) incubation resulted in lower growth. Fe3+ starvation on the other hand showed very poor growth up to 4th day but once the growth started it reached at significant level on 7th day. Higher Fe3+ concentration reflected reduced growth with lethality at 500 microM Fe3+. Chlorophyll a fluorescence under Fe3+ stress reflected almost the similar results as in case of growth. However, the pigment was found to be more sensitive as compared to protein under Fe3+ stress. Similar results have been observed in case of NO3-uptake with only 80% reduction in nutrient uptake in 500 microM Fe3+ incubated cells. Nitrate reductase activity was lower in Fe3+ starved cells as compared to significant enzyme activity in 20 and 50 microM Fe3+ incubated cells. Similar to nitrate reductase, glutamine synthetase also showed maximum level in 50 microM Fe3+ added cells, however, higher Fe3+ concentration (300-500 microM ) resulted in reduced enzymatic activity. Glutamine synthetase activity was less sensitivity as compared to nitrate reductase activity under Fe3+ stress. ATPase (Mg2+ and Ca2+ dependent) always showed higher level with increasing Fe3+ concentration.

Disruption of the uptake hydrogenase gene, but not of the bidirectional hydrogenase gene, leads to enhanced photobiological hydrogen production by the nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120

In order to determine the effects of the deletion of hydrogenase genes on nitrogenase-based photobiological H(2) productivity by heterocystous N(2)-fixing cyanobacteria, we have constructed three hydrogenase mutants from Anabaena sp. PCC 7120: hupL(-) (deficient in the uptake hydrogenase), hoxH(-) (deficient in the bidirectional hydrogenase), and hupL(-)/ hoxH(-) (deficient in both genes). The hupL(-) mutant produced H(2) at a rate four to seven times that of the wild-type under optimal conditions. The hoxH(-) mutant produced significantly lower amounts of H(2) and had slightly lower nitrogenase activity than wild-type. H(2) production by the hupL(-)/ hoxH(-) mutant was slightly lower than, but almost equal to, that of the hupL(-) mutant. The efficiency of light energy conversion to H(2) by the hupL(-) mutant at its highest H(2) production stage was 1.2% at an actinic visible light intensity of 10 W/m(2) (PAR) under argon atmosphere. These results indicate that deletion of the hupL gene could be employed as a source for further improvement of H(2) production in a nitrogenase-based photobiological H(2) production system.

Regulation of cellular differentiation in filamentous cyanobacteria in free-living and plant-associated symbiotic growth states

Certain filamentous nitrogen-fixing cyanobacteria generate signals that direct their own multicellular development. They also respond to signals from plants that initiate or modulate differentiation, leading to the establishment of a symbiotic association. An objective of this review is to describe the mechanisms by which free-living cyanobacteria regulate their development and then to consider how plants may exploit cyanobacterial physiology to achieve stable symbioses. Cyanobacteria that are capable of forming plant symbioses can differentiate into motile filaments called hormogonia and into specialized nitrogen-fixing cells called heterocysts. Plant signals exert both positive and negative regulatory control on hormogonium differentiation. Heterocyst differentiation is a highly regulated process, resulting in a regularly spaced pattern of heterocysts in the filament. The evidence is most consistent with the pattern arising in two stages. First, nitrogen limitation triggers a nonrandomly spaced cluster of cells (perhaps at a critical stage of their cell cycle) to initiate differentiation. Interactions between an inhibitory peptide exported by the differentiating cells and an activator protein within them causes one cell within each cluster to fully differentiate, yielding a single mature heterocyst. In symbiosis with plants, heterocyst frequencies are increased 3- to 10-fold because, we propose, either differentiation is initiated at an increased number of sites or resolution of differentiating clusters is incomplete. The physiology of symbiotically associated cyanobacteria raises the prospect that heterocyst differentiation proceeds independently of the nitrogen status of a cell and depends instead on signals produced by the plant partner.

Monitoring of chemical fertilizers on toxicity of two carbamate insecticides to the cyanobacterium Anabaena PCC 7120

The effects of individual chemical fertilizers (urea, superphosphate and potash) on the toxicity of two carbamate insecticides (carbaryl and carbofuran) to the nitrogen-fixing cyanobacterium Anabaena PCC 7120, were studied in vitro at partial lethal levels of each insecticide. Urea at 10 and 50 ppm levels reduced the toxicity due to carbaryl at 50 ppm partial lethal dose and due to carbofuran at 100 and 250 ppm partial lethal doses. Urea at 100 ppm enchanced the toxicity of both insecticides. Superphosphate at 10 ppm reduced the toxicity of carbaryl at 50 ppm and carbofuran at 100 and 250 ppm, but it enhanced the toxicity due to both insecticides at 50 ppm superphosphate. The toxicity due to carbaryl at 40 and 60 ppm were reduced by 100 and 200 ppm potash, but higher potash levels caused enhancement of toxicity. Carbofuran toxicity at 100 ppm was reduced but at 250 ppm the toxicity was enhanced with 100 ppm potash. Urea, superphosphate and potash caused no significant change in number of vegetative cells between the successive heterocysts at 10 and 50 ppm of urea and superphosphate, respectively, and 100 ppm of potash.

Toxicity of two carbamate insecticides to the cyanobacterium Anabaena PCC 7120 and computations of partial lethal concentrations by the probit method

Toxicity studies of two commercial carbamate insecticides, carbaryl and carbofuran with the nitrogen-fixing filamentous cyanobacterium Anabaena PCC 7120, are described. Under nitrogen-fixing conditions and with calcium nitrate supplementation, 100 and 120 ppm carbaryl were the respective lethal concentrations (LC100), while 20 to 80 ppm (nitrogen-fixing conditions) and 20 to 100 ppm (with nitrate supplementation) were the partial lethal doses (<LC100). Under nitrogen-fixing conditions and nitrate supplementation, 100 to 1,000 ppm and 100 to 1,200 ppm were the respective partial lethal concentrations, whereas 1,500 ppm carbofuran was the LC100 for both conditions. In agar media, the highest permissive insecticide concentrations were 60 ppm for carbaryl and 250 ppm for carbofuran; minimum inhibitory concentrations were 10 and 25 ppm; and the LC100 were 80 and 300 ppm, respectively. Computations of percentage lethal data yielded LC25, LC50 and LC75 values by the probit method. The number of vegetative cells between two successive heterocysts decreased. The N-content of the cultures in nitrogen-fixing medium determined by the micro-Kjeldahl method, was affected significantly by both insecticides. Carbofuran was less hazardous than carbaryl to the cyanobacterium.

Algal extracellular products suppress Anabaena flos-aquae heterocyst spacing

Intra- and interspecific chemical signals allow bacteria to respond to environmental conditions by regulating gene transcription. In cyanobacteria, gene products and the presence of fixed nitrogen regulate heterocyst frequency. In this paper, we describe a chemical made by a green alga, Chlamydomonas reinhardtii, that suppresses heterocyst formation in the co-occurring cyanobacterium, Anabaena flos-aquae. Cyanobacterial heterocyst frequencies were reduced in the presence of water-soluble, proteinase- and heat-resistant molecules greater than 15 kDa in molecular size. Green algal cells in all phases of growth made the suppressor. Ammonium and nitrate concentrations in the medium did not correlate with this change in phenotype. In addition, growth rate was not enhanced by the extracellular products. Therefore, C. reinhardtii extracellular products acted as a heterocyst inhibitor, not as a fixed nitrogen source. Chemical interactions between green algae and cyanobacteria influence heterocyst formation, an important consideration in understanding the outcome of competition between these organisms and the dynamics of phytoplankton communities.

Identification and inactivation of three group 2 sigma factor genes in Anabaena sp. strain PCC 7120

Three new Anabaena sp. strain PCC 7120 genes encoding group 2 alternative sigma factors have been cloned and characterized. Insertional inactivation of sigD, sigE, and sigF genes did not affect growth on nitrate under standard laboratory conditions but did transiently impair the abilities of sigD and sigE mutant strains to establish diazotrophic growth. A sigD sigE double mutant, though proficient in growth on nitrate and still able to differentiate into distinct proheterocysts, was unable to grow diazotrophically due to extensive fragmentation of filaments upon nitrogen deprivation. This double mutant could be complemented by wild-type copies of sigD or sigE, indicating some degree of functional redundancy that can partially mask phenotypes of single gene mutants. However, the sigE gene was required for lysogenic development of the temperate cyanophage A-4L. Several other combinations of double mutations, especially sigE sigF, caused a transient defect in establishing diazotrophic growth, manifested as a strong and prolonged bleaching response to nitrogen deprivation. We found no evidence for developmental regulation of the sigma factor genes. luxAB reporter fusions with sigD, sigE, and sigF all showed slightly reduced expression after induction of heterocyst development by nitrogen stepdown. Phylogenetic analysis of cyanobacterial group 2 sigma factor sequences revealed that they fall into several subgroups. Three morphologically and physiologically distant strains, Anabaena sp. strain PCC 7120, Synechococcus sp. strain PCC 7002, and Synechocystis sp. strain PCC 6803 each contain representatives of four subgroups. Unlike unicellular strains, Anabaena sp. strain PCC 7120 has three additional group 2 sigma factors that cluster in subgroup 2.5b, which is perhaps specific for filamentous or heterocystous cyanobacteria.

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.

Regulation of potassium-dependent Kdp-ATPase expression in the nitrogen-fixing cyanobacterium Anabaena torulosa

The KdpB polypeptides in the cyanobacterium Anabaena torulosa were shown to be two membrane-bound proteins of about 78 kDa, expressed strictly under K(+) deficiency and repressed or degraded upon readdition of K(+). In both Anabaena and Escherichia coli strain MC4100, osmotic and ionic stresses caused no significant induction of steady-state KdpB levels during extreme potassium starvation.

Isolation and partial characterization of Het- Fix- mutant strain of the diazotrophic cyanobacterium Anabaena variabilis showing chromatic adaptation

We propose a model to describe the changes taking place in biochemical processes/events to explain the development of heterocyst and nitrogenase in a diazotrophic cyanobacterium Anabaena variabilis. For this purpose, a mutant strain of A. variabilis lacking heterocyst differentiation and incapable of growth with dinitrogen as the sole source of nitrogen has been isolated after nitrosoguanidine (NTG) mutagenesis and selection by penicillin enrichment. The mutant strain (Het- Fix-) thus isolated has morphological variation and was incapable of reducing acetylene under anaerobic conditions, indicating its mutational loss of the process of nitrogen fixation. The Het- Fix- mutant strain had reduced glutamine synthetase (transferase) activity compared with its wild-type counterpart, suggesting a link between nif gene expression and the expression of gln A, the structural gene of GS. The Het- Fix- mutant strain compared with its wild-type strain also had an extremely high level of phycobiliprotein and a low level of carotenoids. Furthermore, the coiling of vegetative filaments in the Het- Fix- mutant strain, which reduced the surface area to be exposed to light, was a direct indication of the chromatic adaptation, because the mutant strain was found to be photosensitive, showing bleaching of the cells under high light intensity.

The effect of 2,5,2',5'-tetrachlorobiphenyl on growth and death of the cyanobacterium Anabaena flos-aquae

The effect of 2,5,2',5'-tetrachlorobiphenyl (TcBP) on cell death was investigated in the cyanobacterium Anabaena flos-aquae (Lyngb.) Bréb grown in a P-limited, semicontinuous culture under N2-fixing conditions during a 17-d period. The TcBP was supplied daily to yield final concentrations of 1, 10, and 100 ppb (or ng/ml). At 1 and 10 ppb, the population size of live cells (sum of live vegetative cells and live heterocysts) was not different from that of the TcBP-free controls (p > 0.1, t test) and remained constant both in its absolute value (9.6 X 10(5) cells/ml) and as a percentage of the total population (98.6%). However, at 100 ppb, the population size of live cells declined significantly after the 11th day (8.2 x 10(5) cells/ml, or 96.6% of total population; p < 0.01, t test). The decrease in viable cells was mostly found in vegetative cells. Bioconcentration factor in the cell ([pg TcBP/g dry wt cells]/[pg TcBP/ml]) was 1.23 x 10(5).

Differential effects of thiobencarb toxicity on growth and photosynthesis of Anabaena variabilis with changes in phosphate level

A thiobencarb dose of 3 mg L(-1) reduced the protein content of Anabaena variabilis, whereas it elevated the carbohydrate content. Measurements of Anabaena growth, photosynthetic activity, and respiration rate revealed that the high dose of phosphate (0.53 mM) exerted no additional toxic effect to thiobencarb toxicity. Recovery of Anabaena cells from the inhibitory effect of thiobencarb occurred immediately after its reculture in herbicide free-medium. Maximum uptake of thiobencarb was associated with high biomass yield.

Chlorophyll a fluorescence and photosynthetic activity as tools for the evaluation of simazine toxicity to Protosiphon botryoides and Anabaena variabilis

On studying the effect of simazine on Protosiphon botryoides and Anabaena variabilis, data revealed that chlorophyll a content and dry weight were decreased with the increase in simazine concentration. High concentration of simazine (0.8 mg L(-1)) reduced gross photosynthesis and carbohydrate content, whereas protein content and respiration rate were increased. Algal cell recovery from simazine toxic effect occurred after 2 and 4 days for Anabaena and Protosiphon, respectively, which may be attributed to the difference in algal genotype of the tested organisms.

Simultaneous occurrence of two different glyceraldehyde-3-phosphate dehydrogenases in heterocystous N(2)-fixing cyanobacteria

Enzyme activity determinations and Western and Northern blot analyses have shown the presence of two catalytically different glyceraldehyde-3-phosphate dehydrogenases (GAPDH) in both vegetative cells and heterocysts of several N(2)-fixing Anabaena strains: (a) the gap2-encoded NAD(P)-dependent GAPDH2 (EC 1.2.1.59), the enzyme involved in the photosynthetic carbon assimilation pathway, which is present at higher levels in vegetative cells, and (b) the gap3-encoded NAD-dependent GAPDH3 (EC 1.2.1.12), presumably involved in carbohydrate anabolism and catabolism, which is the predominant GAPDH in heterocysts. In contrast, the gap1-encoded GAPDH1, which is the other NAD-dependent cyanobacterial GAPDH, is virtually absent in both cell types. These findings are discussed in the context of carbon metabolism of heterocystous N(2)-fixing cyanobacteria.

A screen for sequences up-regulated during heterocyst development in Anabaena sp. strain PCC 7120

A plasmid library of small genomic fragments from the cyanobacterium Anabaena sp. strain PCC 7120 was screened for sequences whose transcripts increase in abundance during a heterocyst development time course. A total of 350 clones were analyzed, representing 1-2% of the Anabaena sp. strain PCC 7120 genome. Twenty-seven clones (8%) showed some degree of up-regulation after nitrogen starvation. The increase in transcript abundance ranged from 1.2-fold to 3.5-fold. Further analysis of the expression of some of the sequences using Northern blots suggested that the up-regulation values calculated from the screen are underestimates. The collection of up-regulated clones includes novel genes, previously characterized genes, and genes identifiable by similarity to known genes. One of the novel genes has been shown to be required for heterocyst function, and the sequence similarities and expression patterns of some of the others suggest that they may play a role in heterocyst development.

PatS and products of nitrogen fixation control heterocyst pattern

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 forms a developmental pattern of single heterocysts separated by approximately 10 vegetative cells. Heterocysts differentiate from vegetative cells and are specialized for nitrogen fixation. The patS gene, which encodes a small peptide that inhibits heterocyst differentiation, is expressed in proheterocysts and plays a critical role in establishing the heterocyst pattern. Here we present further analysis of patS expression and heterocyst pattern formation. A patS-gfp reporter strain revealed clusters of patS-expressing cells during the early stage of heterocyst differentiation. PatS signaling is likely to be involved in the resolution of these clusters. Differentiating cells were inhibited by PatS during the time period 6 to 12 h after heterocyst induction, when groups of differentiating cells were being resolved to a single proheterocyst. Increased transcription of patS during development coincided with expression from a new transcription start site. In vegetative cells grown on nitrate, the 5' end of a transcript for patS was localized 314 bases upstream from the first translation initiation codon. After heterocyst induction, a new transcript with a 5' end at -39 bases replaced the vegetative cell transcript. A patS mutant grown for several days under nitrogen-fixing conditions showed partial restoration of the normal heterocyst pattern, presumably because of a gradient of nitrogen compounds supplied by the heterocysts. The patS mutant formed heterocysts when grown in the presence of nitrate but showed no nitrogenase activity and no obvious heterocyst pattern. We conclude that PatS and products of nitrogen fixation are the main signals determining the heterocyst pattern.

Environmental and nutritional factors affecting geosmin synthesis by Anabaena sp

A cyanobacterium isolated from a source-water reservoir during a spring odor and taste episode and identified as Anabaena sp. consistently produced geosmin during laboratory culture on modified BG-11 liquid medium. Maximal geosmin/biomass occurred at 20 degrees C and a light intensity of 17 microE/m2/s; geosmin/chla values directly correlated with increasing light intensity (r2 = 0.95, P < 0.01). It was concluded that at 20 degrees C, increasing light intensity favors less chla synthesis and higher geosmin synthesis; at 17 microE/m2/s, increasing temperature stimulates chla production (to 25 degrees C) while repressing geosmin synthesis (above 20 degrees C). Nutritional factors promoting biomass, chla, and geosmin synthesis by Anabaena sp. were also investigated. For cultures grown at 17 microE/m2/s and 20 degrees C for 20 days, both ammonium-N and nitrate-N generally enhanced the growth of Anabaena sp. Nitrate-N promoted more chla production (r2 = 0.99) than ammonium-N. Geosmin synthesis was directly correlated with ammonium-N concentrations (r2 = 0.89), with low nitrate-N (123.5 micrograms/l) favoring maximal geosmin production (2.8 micrograms/l). Increasing nitrate-N concentrations promoted a three-fold increase in chla content with geosmin synthesis decreased by two-fold. Geosmin/mg biomass was directly related to ammonium-N concentration; high nitrate-N levels suppressed geosmin production. No geosmin was detected at or below 118 micrograms phosphate-phosphorus/l. Geosmin, dry weight biomass, and chla production were correlated with increasing phosphorus (P) concentration (r2 = 0.76, 0.96 and 0.98, respectively). No geosmin was detected when copper was present in growth media at or above 6.92 micrograms Cu2+/l (CuSO4.5H2O). Dry weight biomass and chla production were negatively correlated with Cu2+ ion concentrations.

A mutant of the cyanobacterium Anabaena variabilis ATCC 29413 lacking cyanophycin synthetase: growth properties and ultrastructural aspects

The gene cphA encoding cyanophycin synthetase was interrupted in Anabaena variabilis ATCC 29413 by insertional mutagenesis. The mutant lacked cyanophycin granules and the polar nodules of heterocysts. The mutant grew as fast as the wild-type irrespective of the nitrogen source at low light intensity whereas growth on N(2) was somewhat reduced in high light. It is concluded that cyanophycin metabolism and polar nodules are not essential for aerobic N(2) fixation.

Effect on heterocyst differentiation of nitrogen fixation in vegetative cells of the cyanobacterium Anabaena variabilis ATCC 29413

Heterocysts are terminally differentiated cells of some filamentous cyanobacteria that fix nitrogen for the entire filament under oxic growth conditions. Anabaena variabilis ATCC 29413 is unusual in that it has two Mo-dependent nitrogenases; one, called Nif1, functions in heterocysts, while the second, Nif2, functions under anoxic conditions in vegetative cells. Both nitrogenases depended on expression of the global regulatory protein NtcA. It has long been thought that a product of nitrogen fixation in heterocysts plays a role in maintenance of the spaced pattern of heterocyst differentiation. This model assumes that each cell in a filament senses its own environment in terms of nitrogen sufficiency and responds accordingly in terms of differentiation. Expression of the Nif2 nitrogenase under anoxic conditions in vegetative cells was sufficient to support long-term growth of a nif1 mutant; however, that expression did not prevent differentiation of heterocysts and expression of the nif1 nitrogenase in either the nif1 mutant or the wild-type strain. This suggested that the nitrogen sufficiency of individual cells in the filament did not affect the signal that induces heterocyst differentiation. Perhaps there is a global mechanism by which the filament senses nitrogen sufficiency or insufficiency based on the external availability of fixed nitrogen. The filament would then respond by producing heterocyst differentiation signals that affect the entire filament. This does not preclude cell-to-cell signaling in the maintenance of heterocyst pattern but suggests that overall control of the process is not controlled by nitrogen insufficiency of individual cells.

Changes in carboxysome structure and grouping and in photosynthetic affinity for inorganic carbon in Anabaena strain PCC 7119 (Cyanophyta) in response to modification of CO2 and Na+ supply

In ANABAENA: PCC 7119 a 4-fold decrease in the value of the apparent photosynthetic affinity for external inorganic carbon [K1/2 (Ci)] occurred between 9 and 12 h after the transfer from high-CO2 (2% CO2-enriched air) to air-growing conditions. A slight increase in carboxysome frequency occurred, but during this transition their appearance and distribution remained unchanged. ANABAENA: PCC 7119 did not improve its K1/2 (Ci) beyond the above cited level of acclimation neither by culturing the cyanobacteria in Na+-deficient medium in air nor by aeration with CO2-depleted air. In air-grown cultures, Na+ deficiency induced a large increase in carboxysome frequency and an alteration of their appearance: the greatest proportion were electron-dense whereas this type constituted a minority in high-CO2 and in air, Na+-sufficient conditions. It also induced major changes in carboxysome distribution, whereby more than 60% were grouped, compared with only 10% in high-CO2 and in air, Na+-sufficient conditions. These changes in carboxysome expression were extremely rapid, occurring mainly during the first 2 h.

Ultrastructure of the fresh water cyanobacterium Anabaena variabilis SPU 003 and its application for oxygen-free hydrogen production

Photoproduction of hydrogen has been studied as one of the ways to produce a clean, renewable energy source. Ultrastructure of the selected strain Anabaena variabilis SPU 003, a heterocystous cyanobacterium, has been done to understand the cell structure. The organism was found to be essentially a dark hydrogen producer. While pH had no significant effect on hydrogen production, optimum temperature was found to be 30 degrees C. Various sugars increased the production of hydrogen while the presence of various nitrogen sources inhibits the production. The production of hydrogen is highly sensitive to salinity and micronutrients.