Synergistic regulation of hydrogen sulfide and nitric oxide on biochemical components, exopolysaccharides, and nitrogen metabolism in nickel stressed rice field cyanobacteria

The present study examined the regulatory mechanism of hydrogen sulfide (H2S) and nitric oxide (NO) in nickel (Ni) stressed cyanobacteria viz., Nostoc muscorum and Anabaena sp. by analyzing growth, photosynthetic pigments, biochemical components (protein and carbohydrate), exopolysaccharides (EPS), inorganic nitrogen content, and activity of enzymes comprised in nitrogen metabolism and Ni accumulation. The 1 µM Ni substantially diminished growth by 18% and 22% in N. muscorum and Anabaena sp. respectively, along with declining the pigment contents (Chl a/Car ratio and phycobiliproteins), and biochemical components. It also exerted negative impacts on inorganic uptake of nitrate and nitrite contents; nitrate reductase and nitrite reductase; and ammonium assimilating enzymes (glutamine synthetase, glutamate synthase, and glutamate dehydrogenase exhibited a reverse trend) activities. Nonetheless, the adverse impact of Ni can be mitigated through the exogenous supplementation of NaHS [sodium hydrosulfide (8 µM); H2S donor] and SNP [sodium nitroprusside (10 µM); NO donor] which showed substantial improvement on growth, pigments, nitrogen metabolism, and EPS layer and noticeably occurred as a consequence of a substantial reduction in Ni accumulation content which minimized the toxicity effects. The accumulation of Ni on both the cyanobacterial cell surface (EPS layer) are confirmed by the SEM-EDX analysis. Further, the addition of NO scavenger (PTIO; 20 µM) and inhibitor of NO (L-NAME; 100 µM); and H2S scavenger (HT; 20 µM) and H2S inhibitor (PAG; 50 µM) reversed the positive responses of H2S and NO and damages were more prominent under Ni stress thereby, suggesting the downstream signaling of H2S on NO-mediated alleviation. Thus, this study concludes the crosstalk mechanism of H2S and NO in the mitigation of Ni-induced toxicity in rice field cyanobacteria.

A TonB-Like Protein, SjdR, Is Involved in the Structural Definition of the Intercellular Septa in the Heterocyst-Forming Cyanobacterium Anabaena

Cyanobacteria are photosynthetic organisms with a Gram-negative envelope structure. Certain filamentous species such as Anabaena sp. strain PCC 7120 can fix dinitrogen upon depletion of combined nitrogen. Because the nitrogen-fixing enzyme, nitrogenase, is oxygen sensitive, photosynthesis and nitrogen fixation are spatially separated in Anabaena. Nitrogen fixation takes place in specialized cells called heterocysts, which differentiate from vegetative cells. During heterocyst differentiation, a microoxic environment is created by dismantling photosystem II and restructuring the cell wall. Moreover, solute exchange between the different cell types is regulated to limit oxygen influx into the heterocyst. The septal zone containing nanopores for solute exchange is constricted between heterocysts and vegetative cells, and cyanophycin plugs are located at the heterocyst poles. We identified a protein previously annotated as TonB1 that is largely conserved among cyanobacteria. A mutant of the encoding gene formed heterocysts but was impaired in diazotrophic growth. Mutant heterocysts appeared elongated and exhibited abnormal morphological features, including a reduced cyanophycin plug, an enhanced septum size, and a restricted nanopore zone in the septum. In spite of this, the intercellular transfer velocity of the fluorescent marker calcein was increased in the mutant compared to the wild type. Thus, the protein is required for proper formation of septal structures, expanding our emerging understanding of Anabaena peptidoglycan plasticity and intercellular solute exchange, and is therefore renamed SjdR (septal junction disk regulator). Notably, calcium supplementation compensated for the impaired diazotrophic growth and alterations in septal peptidoglycan in the sjdR mutant, emphasizing the importance of calcium for cell wall structure. IMPORTANCE Multicellularity in bacteria confers an improved adaptive capacity to environmental conditions and stresses. This includes an enhanced capability of resource utilization through a distribution of biochemical processes between constituent cells. This specialization results in a mutual dependency of different cell types, as is the case for nitrogen-fixing heterocysts and photosynthetically active vegetative cells in Anabaena. In this cyanobacterium, intercellular solute exchange is facilitated through nanopores in the peptidoglycan between adjacent cells. To ensure functionality of the specialized cells, septal size as well as the position, size, and frequency of nanopores in the septum need to be tightly established. The novel septal junction disk regulator SjdR characterized here is conserved in the cyanobacterial phylum. It influences septal size and septal nanopore distribution. Consequently, its absence severely affects the intercellular communication and the strains' growth capacity under nitrogen depletion. Thus, SjdR is involved in septal structure remodeling in cyanobacteria.

Calm on the surface, dynamic on the inside. Molecular homeostasis of Anabaena sp. PCC 7120 nitrogen metabolism

Nitrogen sources are all converted into ammonium/ia as a first step of assimilation. It is reasonable to expect that molecular components involved in the transport of ammonium/ia across biological membranes connect with the regulation of both nitrogen and central metabolism. We applied both genetic (i.e., Δamt mutation) and environmental treatments to a target biological system, the cyanobacterium Anabaena sp PCC 7120. The aim was to both perturb nitrogen metabolism and induce multiple inner nitrogen states, respectively, followed by targeted quantification of key proteins, metabolites and enzyme activities. The absence of AMT transporters triggered a substantial whole-system response, affecting enzyme activities and quantity of proteins and metabolites, spanning nitrogen and carbon metabolisms. Moreover, the Δamt strain displayed a molecular fingerprint indicating nitrogen deficiency even under nitrogen replete conditions. Contrasting with such dynamic adaptations was the striking near-complete lack of an externally measurable altered phenotype. We conclude that this species evolved a highly robust and adaptable molecular network to maintain homeostasis, resulting in substantial internal but minimal external perturbations. This analysis provides evidence for a potential role of AMT transporters in the regulatory/signalling network of nitrogen metabolism and the existence of a novel fourth regulatory mechanism controlling glutamine synthetase activity.

Conditioning film formation and its influence on the initial adhesion and biofilm formation by a cyanobacterium on photobioreactor materials

Although cyanobacteria are a common group of microorganisms well-suited to utilization in photobioreactors (PBRs), studies of cyanobacteria fouling and its prevention are scarce. Using a cyanobacterium, Anabaena sp. PCC 7120, which had been genetically modified to enhance linalool production, the formation of conditioning films and the effects of these on the physico-chemical surface properties of various PBR materials during initial adhesion and biofilm formation were investigated. The adhesion assay revealed that the overall attachment of Anabaena was substratum dependent and no correlation between the hydrophobicity/roughness of clean material and cell attachment was found. Surface hydrophilicity/hydrophobicity of all the materials changed within 12 h due to formation of conditioning films. ATR-FTIR spectroscopy revealed that the fractional change in protein deposition between 12 to 96 h was consistent with Anabaena cell attachment but polysaccharide deposition was material specific and did not correlate with cell attachment on the PBR materials. Also, the delay in conditioning film proteins on PVC and PTFE indicated that components other than proteins may be responsible for the decrease in contact angles on these surfaces within 12 h. This indicates the important role of the chemical nature of adsorbed conditioning films in determining the initial attachment of Anabaena to PBR materials. The lower rate of attachment of Anabaena on the hydrophilic surfaces (glass and PMMA) between 72 h to 96 h (regime 3) showed that these surfaces could potentially have low fouling characteristics at extended time scales and should be considered for further research.

Disruption of the Gene trx-m1 Impedes the Growth of Anabaena sp. PCC 7120 under Nitrogen Starvation

Cyanobacteria possess a sophisticated photosynthesis-based metabolism with admirable plasticity. This plasticity is possible via the deep regulation network, the thiol-redox regulations operated by thioredoxin (hereafter, Trx). In this context, we characterized the Trx-m1-deficient mutant strain of Anabaena sp., PCC 7120 (shortly named A.7120), cultivated under nitrogen limitation. Trx-m1 appears to coordinate the nitrogen response and its absence induces large changes in the proteome. Our data clearly indicate that Trx-m1 is crucial for the diazotrophic growth of A.7120. The lack of Trx-m1 resulted in a large differentiation of heterocysts (>20% of total cells), which were barely functional probably due to a weak expression of nitrogenase. In addition, heterocysts of the mutant strain did not display the usual cellular structure of nitrogen-fixative cells. This unveiled why the mutant strain was not able to grow under nitrogen starvation.

The Individual and Combined Effects of the Cyanotoxins, Anatoxin-a and Microcystin-LR, on the Growth, Toxin Production, and Nitrogen Fixation of Prokaryotic and Eukaryotic Algae

Globally, eutrophication and warming of aquatic ecosystems has increased the frequency and intensity of cyanobacterial blooms and their associated toxins, with the simultaneous detection of multiple cyanotoxins often occurring. Despite the co-occurrence of cyanotoxins such as microcystins and anatoxin-a (ATX) in water bodies, their effects on phytoplankton communities are poorly understood. The individual and combined effects of microcystin-LR (MC-LR) and ATX on the cyanobacteria Microcystis spp., and Anabaena variabilis (a.k.a. Trichormus variabilis), and the chlorophyte, Selenastrum capricornutum were investigated in the present study. Cell density, chlorophyll-a content, and the maximum quantum efficiency of photosystem II (Fv/Fm) of Microcystis cells were generally lowered after exposure to ATX or MC-LR, while the combined treatment with MC-LR and ATX synergistically reduced the chlorophyll-a concentration of Microcystis strain LE-3. Intracellular levels of microcystin in Microcystis LE-3 significantly increased following exposure to MC-LR + ATX. The maximum quantum efficiency of photosystem II of Anabaena strain UTEX B377 declined during exposure to the cyanotoxins. Nitrogen fixation by Anabaena UTEX B377 was significantly inhibited by exposure to ATX, but was unaffected by MC-LR. In contrast, the combination of both cyanotoxins (MC-LR + ATX) caused a synergistic increase in the growth of S. capricornutum. While the toxins caused an increase in the activity of enzymes that scavenge reactive oxygen species in cyanobacteria, enzyme activity was unchanged or decreased in S. capricornutum. Collectively this study demonstrates that MC-LR and ATX can selectively promote and inhibit the growth and performance of green algae and cyanobacteria, respectively, and that the combined effect of these cyanotoxins was often more intense than their individual effects on some strains. This suggests that the release of multiple cyanotoxins in aquatic ecosystems, following the collapse of blooms, may influence the succession of plankton communities.

The Absence of Thioredoxin m1 and Thioredoxin C in Anabaena sp. PCC 7120 Leads to Oxidative Stress

Thioredoxin (Trx) family proteins perform redox regulation in cells, and they are involved in several other biological processes (e.g. oxidative stress tolerance). In the filamentous cyanobacterium Anabaena sp. PCC7120 (A. 7120), eight Trx isoforms have been identified via genomic analysis. Among these Trx isoforms, the absence of Trx-m1 and TrxC appears to result in oxidative stress in A. 7120 together with alterations of the thylakoid membrane structure and phycobiliprotein composition. To analyze the physiological changes in these Trx disruptants thoroughly, quantitative proteomics was applied. Certainly, the mutants exhibited similar alterations in the proteome including decreased relative abundance of phycobiliproteins and an increased level of proteins involved in amino acid and carbohydrate metabolism. Nevertheless, the results also indicated that the mutants exhibited changes in the relative abundance of different sets of proteins participating in reactive oxygen species detoxification, such as Fe-SOD in Δtrx-m1 and PrxQ in ΔtrxC, suggesting distinct functions of Trx-m1 and TrxC.

Microalgal cultivation for biofertilization in rice plants using a vertical semi-closed airlift photobioreactor

Nitrogen (N) is one of the most important limiting factors in conventional rice (Oryza sativa) production, which heavily relies on synthetic fertilizers. In this study, we researched on the development and use of a vertical semi-closed airlift photobioreactor (PBR) for microalgal cultivation and subsequently determined the efficacy of microalgae-based fertilizers to rice plant growth. The PBR system was developed to produce two strains of N2-fixing cyanobacteria (Anabaena sp. UTEX 2576, Nostoc muscorum UTEX 2209S), and a polyculture of Chlorella vulgaris (UTEX 2714) and Scenedesmus dimorphus (UTEX 1237). When these biofertilizers were evaluated for rice under the greenhouse conditions, results showed that the rice plant heights treated with polyculture-based microalgal biomass were similar to or better than the urea treatment. The effects of the inoculation of the N2-fixing cyanobacterial inoculation on seedling growth was not statistically significant. In conclusion, the vertical semi-closed system PBR cultivation method developed in this study proved to be a simple and effective method for cultivating microalgae. Demonstration of the reliable production system for N2-fixing cyanobacteria and chlorophytes at a medium scale could potentially open the future application of microalgal biofertilizers in rice production.

Hydrogen peroxide treatment promotes chlorophytes over toxic cyanobacteria in a hyper-eutrophic aquaculture pond

Controlling blooms of toxigenic phytoplankton, including cyanobacteria, is a high priority for managers of aquatic systems that are used for drinking water, recreation, and aquaculture production. Although a variety of treatment approaches exist, hydrogen peroxide (H₂O₂) has the potential to be an effective and ecofriendly algaecide given that this compound may select against cyanobacteria while not producing harmful residues. To broadly evaluate the effectiveness of H₂O₂ on toxigenic phytoplankton, we tested multiple concentrations of H₂O₂ on (1) four cyanobacterial cultures, including filamentous Anabaena, Cylindrospermopsis, and Planktothrix, and unicellular Microcystis, in a 5-day laboratory experiment and (2) a dense cyanobacterial bloom in a 7-day field experiment conducted in a nutrient-rich aquaculture pond. In the laboratory experiment, half-maximal effective concentrations (EC₅₀) were similar for Anabaena, Cylindrospermopsis, and Planktothrix (average EC₅₀ = 0.41 mg L^-1) but were ∼10x lower than observed for Microcystis (EC₅₀ = 5.06 mg L^-1). Results from a field experiment in an aquaculture pond showed that ≥1.3 and ≥ 6.7 mg L^-1 of H₂O₂ effectively eliminated Planktothrix and Microcystis, respectively. Moreover, 6.7 mg L^-1 of H₂O₂ reduced microcystin and enhanced phytoplankton diversity, while causing relatively small negative effects on zooplankton abundance. In contrast, 20 mg L^-1 of H₂O₂ showed the greatest negative effect on zooplankton. Our results demonstrate that H₂O₂ can be an effective, rapid algaecide for controlling toxigenic cyanobacteria when properly dosed.

Arsenic uptake, transformation, and release by three freshwater algae under conditions with and without growth stress

This study was carried out using indoor controlled experiments to study the arsenic (As) uptake, biotransformation, and release behaviors of freshwater algae under growth stress. Three freshwater algae, Microcystis aeruginosa, Anabaena flosaquae, and Chlorella sp., were chosen. Two types of inhibitors, e.g., Cu²⁺ and isothiazolinone, were employed to inhibit the growth of the algae. The algae were cultivated to a logarithmic stage in growth media containing 0.1 mg/L P; then, 0.8 mg/L As in the form of arsenate (iAs^V) was added, while both inhibitors were simultaneously added at dosages of 0.1 and 0.3 mg/L, with no addition of inhibitors in the control. After 2 days of exposure, the average growth rate (μ_2d) was measured to represent the growth rates of the algae cells; the extra- and intracellular As concentrations in various forms, i.e., arsenate, arsenite (iAs^III), monomethyl arsenic (MMA), and dimethyl arsenic (DMA), were also measured. Without inhibitors, the average growth rate followed the order of M. aeruginosa, Chlorella sp., and A. flosaquae, with the growth rate of M. aeruginosa significantly higher than that of the other two algae. However, when Cu²⁺ was added as an external inhibitor, the order of the average growth rate for the three algae became partially reversed, suggesting differentiation of the algae in response to the inhibitor. This differentiation can be seen by the reduction in the average growth rate of M. aeruginosa, which was as high as 1730% at the 0.3-mg/L Cu²⁺ dosage when compared with the control, while for the other two algae, much fewer changes were seen. The great reduction in M. aeruginosa growth rate was accompanied by increases in extracellular iAs^V and iAs^III and intracellular iAs^V concentrations in the algae, indicating that As transformation is related to the growth of this algae. Much fewer or neglectable changes in growth were observed that were consistent with the few changes in the extra- and intracellular As speciation for the other two algae with Cu²⁺ inhibition and all the three algae with isothiazolinone inhibition, corroborating the above hypothesis again. All the algae tested in this study demonstrated great abilities for As transformation and release, as seen by the much higher rates of 86.11-99.98% and 81.11-99.89% for transformation and release when compared to the control, respectively. When inhibitors were added, the transformation and release values of only A. flosaquae decreased remarkably down to 72.37-86.79% and 64.67-85.24%, respectively, while no changes were seen for these values in the other two algae, indicating that growth stress did not affect the As transformation and release of the other algae. The biological productivity of As by the three algae followed the order of M. aeruginosa, Chlorella sp., and A. flosaquae, which was generally consistent with the As transformation and release in conditions with and without inhibitors, suggesting that the As behavior in the algae that was related to growth stress largely differed among algae species.

Quantification of cyanobacterial cells via a novel imaging-driven technique with an integrated fluorescence signature

A novel imaging-driven technique with an integrated fluorescence signature to enable automated enumeration of two species of cyanobacteria and an alga of somewhat similar morphology to one of the cyanobacteria is presented to demonstrate proof-of-concept that high accuracy, imaging-based, rapid water quality analysis can be with conventional equipment available in typical water quality laboratories-this is not currently available. The results presented herein demonstrate that the developed method identifies and enumerates cyanobacterial cells at a level equivalent to or better than that achieved using standard manual microscopic enumeration techniques, but in less time, and requiring significantly fewer resources. When compared with indirect measurement methods, the proposed method provides better accuracy at both low and high cell concentrations. It extends the detection range for cell enumeration while maintaining accuracy and increasing enumeration speed. The developed method not only accurately estimates cell concentrations, but it also reliably distinguishes between cells of Anabaena flos-aquae, Microcystis aeruginosa, and Ankistrodesmus in mixed cultures by taking advantage of additional contrast between the target cell and complex background gained under fluorescent light. Thus, the proposed image-driven approach offers promise as a robust and cost-effective tool for identifying and enumerating microscopic cells based on their unique morphological features.

Stress effects of cyanotoxin β-methylamino-L-alanine (BMAA) on cyanobacterial heterocyst formation and functionality

Various species of cyanobacteria, diatoms and dinoflagellates are capable of synthesizing the non-proteinogenic neurotoxic amino acid β-N-methylamino-L-alanine (BMAA), which is known to be a causative agent of human neurodegeneration. Similar to most cyanotoxins, the biological and ecological functions of BMAA in cyanobacteria are unknown. In this study, we show for the first time that BMAA, in micromolar amounts, inhibits the formation of heterocysts (specialized nitrogen-fixing cells) in heterocystous, diazotrophic cyanobacteria [Anabaena sp. PCC 7120, Nostoc punctiforme PCC 73102 (ATCC 29133), Nostoc sp. strain 8963] under conditions of nitrogen starvation. The inhibitory effect of BMAA is abolished by the addition of glutamate. To understand the genetic reason for the observed phenomenon, we used qPCR to study the expression of key genes involved in cell differentiation and nitrogen metabolism in the model cyanobacterium Anabaena sp. PCC 7120. We observed that in the presence of BMAA, Anabaena sp. PCC 7120 does not express two essential genes associated with heterocyst differentiation, namely, hetR and hepA. We also found that addition of BMAA to cyanobacterial cultures with mature heterocysts inhibits nifH gene expression and nitrogenase activity.

Physiological responses to salt stress of salt-adapted and directly salt (NaCl and NaCl+Na2SO4 mixture)-stressed cyanobacterium Anabaena fertilissima

Soil salinity in nature is generally mixed type; however, most of the studies on salt toxicity are performed with NaCl and little is known about sulfur type of salinity (Na₂SO₄). Present study discerns the physiologic mechanisms responsible for salt tolerance in salt-adapted Anabaena fertilissima, and responses of directly stressed parent cells to NaCl and NaCl+Na₂SO₄ mixture. NaCl at 500 mM was lethal to the cyanobacterium, whereas salt-adapted cells grew luxuriantly. Salinity impaired gross photosynthesis, electron transport activities, and respiration in parent cells, but not in the salt-adapted cells, except a marginal increase in PSI activity. Despite higher Na⁺ concentration in the salt mixture, equimolar NaCl appeared more inhibitive to growth. Sucrose and trehalose content and antioxidant activities were maximal in 250 mM NaCl-treated cells, followed by salt mixture and was almost identical in salt-adapted (exposed to 500 mm NaCl) and control cells, except a marginal increase in ascorbate peroxidase activity and an additional fourth superoxide dismutase isoform. Catalase isoform of 63 kDa was induced only in salt-stressed cells. Salinity increased the uptake of intracellular Na⁺ and Ca²⁺ and leakage of K⁺ in parent cells, while cation level in salt-adapted cells was comparable to control. Though there was differential increase in intracellular Ca²⁺ under different salt treatments, ratio of Ca²⁺/Na⁺ remained the same. It is inferred that stepwise increment in the salt concentration enabled the cyanobacterium to undergo priming effect and acquire robust and efficient defense system involving the least energy.

Robust stochastic Turing patterns in the development of a one-dimensional cyanobacterial organism

Under nitrogen deprivation, the one-dimensional cyanobacterial organism Anabaena sp. PCC 7120 develops patterns of single, nitrogen-fixing cells separated by nearly regular intervals of photosynthetic vegetative cells. We study a minimal, stochastic model of developmental patterns in Anabaena that includes a nondiffusing activator, two diffusing inhibitor morphogens, demographic fluctuations in the number of morphogen molecules, and filament growth. By tracking developing filaments, we provide experimental evidence for different spatiotemporal roles of the two inhibitors during pattern maintenance and for small molecular copy numbers, justifying a stochastic approach. In the deterministic limit, the model yields Turing patterns within a region of parameter space that shrinks markedly as the inhibitor diffusivities become equal. Transient, noise-driven, stochastic Turing patterns are produced outside this region, which can then be fixed by downstream genetic commitment pathways, dramatically enhancing the robustness of pattern formation, also in the biologically relevant situation in which the inhibitors' diffusivities may be comparable.

Multiple ABC glucoside transporters mediate sugar-stimulated growth in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120

Cyanobacteria are generally capable of photoautotrophic growth and are widely distributed on Earth. The model filamentous, heterocyst-forming strain Anabaena sp. PCC 7120 has long been considered as a strict photoautotroph but is now known to be able to assimilate fructose. We have previously described two components of ABC glucoside uptake transporters from Anabaena that are involved in uptake of the sucrose analog esculin: GlsC [a nucleotide-binding domain subunit (NBD)] and GlsP [a transmembrane component (TMD)]. Here, we created Anabaena mutants of genes encoding three further ABC transporter components needed for esculin uptake: GlsD (NBD), GlsQ (TMD) and GlsR (periplasmic substrate-binding protein). Phototrophic growth of Anabaena was significantly stimulated by sucrose, fructose and glucose. Whereas the glsC and glsD mutants were drastically hampered in sucrose-stimulated growth, the different gls mutants were generally impaired in sugar-dependent growth. Our results suggest the participation of Gls and other ABC transporters encoded in the Anabaena genome in sugar-stimulated growth. Additionally, Gls transporter components influence the function of septal junctions in the Anabaena filament. We suggest that mixotrophic growth is important in cyanobacterial physiology and may be relevant for the wide success of these organisms in diverse environments.

Synergic use of chemical and ecotoxicological tools for evaluating multi-contaminated soils amended with iron oxides-rich materials

Abandoned waste piles from ancient mining activities are potential hot spots for the pollution of the surrounding areas. A pot experiment was carried out to check the potential toxicity of the dumping material present in one of these scenarios, and several amendments were tested to attenuate the spread of the contamination events. The waste material had an acid pH and a large total concentration of As and Cu. A dose-response experiment was performed with this material following OCDE 208 test. A proportion 90:10 uncontaminated soil: dumping material (% w/w) was selected for the following experiment, in order to surpass the amount of dumping material that caused 50% reduction in plant growth. Pots were filled with the 90:10 mixture, planted with seeds of Brassica napus and amended with the following materials: three iron oxides of Bayoxide® E33 series, iron (II) sulphate in combination with de-inking paper sludge (Fe+PS), iron oxide-rich rolling mill scale (ROL) and iron oxide-rich cement waste (CEM). Amendment effectiveness evaluation was based on chemical and biological assays: extractable trace element concentration, soil enzymatic activities, inhibition of light emission of V. fischeri and Anabaena sp., B. napus L. fresh weight and screening test for emergence of B. napus L. seedlings. Amendments E33HCF and Fe+PS were the most effective in reducing extractable As and Zn concentration. B. napus weight and dehydrogenase and β-glucosidase activities were positively increased with the two above mentioned treatments but they triggered more toxic effects for V. fischeri luminescence. E33P treatment was the only in which the EC₅₀ was higher than in the control. Anabaena sp. was less sensitive than V. fischeri as its luminescence was not hampered by any treatment. Trace element concentration did not significantly affect the failure in seed emergence. E33HCF and Fe+PS could act as proper amendments as they decreased extractable As and Zn. Further, plant fresh weight, enzymatic activities and some of the bioassays identified the latter treatments as the best ones among those tested here to this type of multi-contaminated soil.

Overexpression of phytochelatin synthase (pcs) enhances abiotic stress tolerance by altering the proteome of transformed Anabaena sp. PCC 7120

The present study provides data on the insertion of an extra copy of phytochelatin synthase (alr0975) in Anabaena sp. PCC 7120. The recombinant strain (AnFPN-pcs) compared to wild type showed approximately 22.3% increase in growth rate under UV-B, NaCl, heat, CuCl₂, carbofuran, and CdCl₂. It also registered 2.25-fold enhanced nitrogenase activity and 5-fold higher phytochelatin production. A comparison of the protein profile of wild type with the recombinant strain revealed that recombinant strain accumulated proteins belonging to the following categories: (i) detoxification (nutrient stress induced DNA binding protein, Mn-SOD, Alr0946 (CalA)), (ii) protein folding and modification (molecular chaperone DnaK, FKBP-type peptidyl-prolyl cis-trans isomerase), (iii) nucleotide and amino acid biosynthesis (dihydroorotase and Ketol-acid reductoisomerase), (iv) photosynthesis and respiration (coproporphyrinogen III oxidase, phycocyanin alpha chain, ferredoxin-NADP⁺ reductase), and (v) transport (sugar transport ATP-binding protein). Thus, it can be concluded that, above category proteins with their respective role in scavenging reactive oxygen species, proper folding of unfolded proteins, and protection of protein from degradation, sustained carbon fixation and energy pool and active transport of sugar together conceivably help the recombinant cyanobacterium (AnFPN-pcs) to cope with abiotic stress employed in the present study. Such recombinant strains have potential for future use as biofertilizer.

Physiological and proteomic analysis of salinity tolerance of the halotolerant cyanobacterium Anabaena sp

The halotolerant cyanobacterium Anabaena sp was grown under NaCl concentration of 0, 170 and 515 mM and physiological and proteomic analysis was performed. At 515 mM NaCl the cyanobacterium showed reduced photosynthetic activities and significant increase in soluble sugar content, proline and SOD activity. On the other hand Anabaena sp grown at 170 mM NaCl showed optimal growth, photosynthetic activities and comparatively low soluble sugar content, proline accumulation and SOD activity. The intracellular Na(+) content of the cells increased both at 170 and 515 mM NaCl. In contrast, the K(+) content of the cyanobacterium Anabaena sp remained stable in response to growth at identical concentration of NaCl. While cells grown at 170 mM NaCl showed highest intracellular K(+)/Na(+) ratio, salinity level of 515 mM NaCl resulted in reduced ratio of K(+)/Na(+). Proteomic analysis revealed 50 salt-responsive proteins in the cyanobacterium Anabaena sp under salt treatment compared with control. Ten protein spots were subjected to MALDI-TOF-MS/MS analysis and the identified proteins are involved in photosynthesis, protein folding, cell organization and energy metabolism. Differential expression of proteins related to photosynthesis, energy metabolism was observed in Anabaena sp grown at 170 mM NaCl. At 170 mM NaCl increased expression of photosynthesis related proteins and effective osmotic adjustment through increased antioxidant enzymes and modulation of intracellular ions contributed to better salinity tolerance and optimal growth. On the contrary, increased intracellular Na(+) content coupled with down regulation of photosynthetic and energy related proteins resulted in reduced growth at 515 mM NaCl. Therefore reduced growth at 515 mM NaCl could be due to accumulation of Na(+) ions and requirement to maintain higher organic osmolytes and antioxidants which is energy intensive. The results thus show that the basis of salt tolerance is different when the halotolerant cyanobacterium Anabaena sp is grown under low and high salinity levels.

Efficient Gene Induction and Endogenous Gene Repression Systems for the Filamentous Cyanobacterium Anabaena sp. PCC 7120

In the last decade, many studies have been conducted to employ genetically engineered cyanobacteria in the production of various metabolites. However, the lack of a strict gene regulation system in cyanobacteria has hampered these attempts. The filamentous cyanobacterium Anabaena sp. PCC 7120 performs both nitrogen and carbon fixation and is, therefore, a good candidate organism for such production. To employ Anabaena cells for this purpose, we intended to develop artificial gene regulation systems to alter the cell metabolic pathways efficiently. We introduced into Anabaena a transcriptional repressor TetR, widely used in diverse organisms, and green fluorescent protein (GFP) as a reporter. We found that anhydrotetracycline (aTc) substantially induced GFP fluorescence in a concentration-dependent manner. By expressing tetR under the nitrate-specific promoter nirA, we successfully reduced the concentration of aTc required for the induction of gfp under nitrogen fixation conditions (to 10% of the concentration needed under nitrate-replete conditions). Further, we succeeded in the overexpression of GFP by depletion of nitrate without the inducer by means of promoter engineering of the nirA promoter. Moreover, we applied these gene regulation systems to a metabolic enzyme in Anabaena and successfully repressed glnA, the gene encoding glutamine synthetase that is essential for nitrogen assimilation in cyanobacteria, by expressing the small antisense RNA for glnA. Consequently, the ammonium production of an ammonium-excreting Anabaena mutant was significantly enhanced. We therefore conclude that the gene regulation systems developed in this study are useful tools for the regulation of metabolic enzymes and will help to increase the production of desired substances in Anabaena.

Dynamics and Cell-Type Specificity of the DNA Double-Strand Break Repair Protein RecN in the Developmental Cyanobacterium Anabaena sp. Strain PCC 7120

DNA replication and repair are two fundamental processes required in life proliferation and cellular defense and some common proteins are involved in both processes. The filamentous cyanobacterium Anabaena sp. strain PCC 7120 is capable of forming heterocysts for N₂ fixation in the absence of a combined-nitrogen source. This developmental process is intimately linked to cell cycle control. In this study, we investigated the localization of the DNA double-strand break repair protein RecN during key cellular events, such as chromosome damaging, cell division, and heterocyst differentiation. Treatment by a drug causing DNA double-strand breaks (DSBs) induced reorganization of the RecN focus preferentially towards the mid-cell position. RecN-GFP was absent in most mature heterocysts. Furthermore, our results showed that HetR, a central player in heterocyst development, was involved in the proper positioning and distribution of RecN-GFP. These results showed the dynamics of RecN in DSB repair and suggested a differential regulation of DNA DSB repair in vegetative cell and heterocysts. The absence of RecN in mature heterocysts is compatible with the terminal nature of these cells.

Pressurized Martian-Like Pure CO2 Atmosphere Supports Strong Growth of Cyanobacteria, and Causes Significant Changes in their Metabolism

Surviving of crews during future missions to Mars will depend on reliable and adequate supplies of essential life support materials, i.e. oxygen, food, clean water, and fuel. The most economical and sustainable (and in long term, the only viable) way to provide these supplies on Martian bases is via bio-regenerative systems, by using local resources to drive oxygenic photosynthesis. Selected cyanobacteria, grown in adequately protective containment could serve as pioneer species to produce life sustaining substrates for higher organisms. The very high (95.3 %) CO₂ content in Martian atmosphere would provide an abundant carbon source for photo-assimilation, but nitrogen would be a strongly limiting substrate for bio-assimilation in this environment, and would need to be supplemented by nitrogen fertilizing. The very high supply of carbon, with rate-limiting supply of nitrogen strongly affects the growth and the metabolic pathways of the photosynthetic organisms. Here we show that modified, Martian-like atmospheric composition (nearly 100 % CO₂) under various low pressure conditions (starting from 50 mbar to maintain liquid water, up to 200 mbars) supports strong cellular growth. Under high CO₂ / low N₂ ratio the filamentous cyanobacteria produce significant amount of H₂ during light due to differentiation of high amount of heterocysts.

Biodegradation of polychlorinated biphenyls (PCBs) by the novel identified cyanobacterium Anabaena PD-1

Polychlorinated biphenyls (PCBs), a class of hazardous pollutants, are difficult to dissipate in the natural environment. In this study, a cyanobacterial strain Anabaena PD-1 showed good resistance against PCB congeners. Compared to a control group, chlorophyll a content decreased 3.7% and 11.7% when Anabaena PD-1 was exposed to 2 and 5 mg/L PCBs for 7 d. This cyanobacterial strain was capable of decomposing PCB congeners which was conclusively proved by determination of chloride ion concentrations in chlorine-free medium. After 7 d, the chloride ion concentrations in PCB-treated groups (1, 2, 5 mg/L) were 3.55, 3.05, and 2.25 mg/L, respectively. The genetic information of strain PD-1 was obtained through 16S rRNA sequencing analysis. The GenBank accession number of 16S rRNA of Anabaena PD-1 was KF201693.1. Phylogenetic tree analysis clearly indicated that Anabaena PD-1 belonged to the genus Anabaena. The degradation half-life of Aroclor 1254 by Anabaena PD-1 was 11.36 d; the total degradation rate for Aroclor 1254 was 84.4% after 25 d. Less chlorinated PCB congeners were more likely to be degraded by Anabaena PD-1 in comparison with highly chlorinated congeners. Meta- and para-chlorines in trichlorodiphenyls and tetrachlorobiphenyls were more susceptible to dechlorination than ortho-chlorines during the PCB-degradation process by Anabaena PD-1. Furthermore, Anabaena PD-1 can decompose dioxin-like PCBs. The percent biodegradation of 12 dioxin-like PCBs by strain PD-1 ranged from 37.4% to 68.4% after 25 days. Results above demonstrate that Anabaena PD-1 is a PCB-degrader with great potential for the in situ bioremediation of PCB-contaminated paddy soils.

On-water remote monitoring robotic system for estimating the patch coverage of Anabaena sp. filaments in shallow water

An on-water remote monitoring robotic system was developed for indirectly estimating the relative density of marine cyanobacteria blooms at the subtidal sandy-rocky beach in Balandra Cove, Baja California Sur, Mexico. The system is based on an unmanned surface vehicle to gather underwater videos of the seafloor for avoiding physical damage on Anabaena sp. cyanobacteria colonies, which grow in tufts of filaments weakly attached to rocks, seagrass, and macroalgae. An on-axis image stabilization mechanism was developed to support a camcorder and minimize wave perturbation while recording underwater digital images of the seafloor. Color image processing algorithms were applied to estimate the patch coverage area and density, since Anabaena sp. filaments exhibit a characteristic green tone. Results of field tests showed the feasibility of the robotic system to estimate the relative density, distribution, and coverage area of cyanobacteria blooms, preventing the possible impact of direct observation. The robotic system could also be used in surveys of other benthos in the sublittoral zone.

Antifungal compounds from cyanobacteria

Cyanobacteria are photosynthetic prokaryotes found in a range of environments. They are infamous for the production of toxins, as well as bioactive compounds, which exhibit anticancer, antimicrobial and protease inhibition activities. Cyanobacteria produce a broad range of antifungals belonging to structural classes, such as peptides, polyketides and alkaloids. Here, we tested cyanobacteria from a wide variety of environments for antifungal activity. The potent antifungal macrolide scytophycin was detected in Anabaena sp. HAN21/1, Anabaena cf. cylindrica PH133, Nostoc sp. HAN11/1 and Scytonema sp. HAN3/2. To our knowledge, this is the first description of Anabaena strains that produce scytophycins. We detected antifungal glycolipopeptide hassallidin production in Anabaena spp. BIR JV1 and HAN7/1 and in Nostoc spp. 6sf Calc and CENA 219. These strains were isolated from brackish and freshwater samples collected in Brazil, the Czech Republic and Finland. In addition, three cyanobacterial strains, Fischerella sp. CENA 298, Scytonema hofmanni PCC 7110 and Nostoc sp. N107.3, produced unidentified antifungal compounds that warrant further characterization. Interestingly, all of the strains shown to produce antifungal compounds in this study belong to Nostocales or Stigonematales cyanobacterial orders.

Spatial fluctuations in expression of the heterocyst differentiation regulatory gene hetR in Anabaena filaments

Under nitrogen deprivation, filaments of the cyanobacterium Anabaena undergo a process of development, resulting in a one-dimensional pattern of nitrogen-fixing heterocysts separated by about ten photosynthetic vegetative cells. Many aspects of gene expression before nitrogen deprivation and during the developmental process remain to be elucidated. Furthermore, the coupling of gene expression fluctuations between cells along a multicellular filament is unknown. We studied the statistics of fluctuations of gene expression of HetR, a transcription factor essential for heterocyst differentiation, both under steady-state growth in nitrogen-rich conditions and at different times following nitrogen deprivation, using a chromosomally-encoded translational hetR-gfp fusion. Statistical analysis of fluorescence at the individual cell level in wild-type and mutant filaments demonstrates that expression fluctuations of hetR in nearby cells are coupled, with a characteristic spatial range of circa two to three cells, setting the scale for cellular interactions along a filament. Correlations between cells predominantly arise from intercellular molecular transfer and less from cell division. Fluctuations after nitrogen step-down can build up on those under nitrogen-replete conditions. We found that under nitrogen-rich conditions, basal, steady-state expression of the HetR inhibitor PatS, cell-cell communication influenced by the septal protein SepJ and positive HetR auto-regulation are essential determinants of fluctuations in hetR expression and its distribution along filaments. A comparison between the expression of hetR-gfp under nitrogen-rich and nitrogen-poor conditions highlights the differences between the two HetR inhibitors PatS and HetN, as well as the differences in specificity between the septal proteins SepJ and FraC/FraD. Activation, inhibition and cell-cell communication lie at the heart of developmental processes. Our results show that proteins involved in these basic ingredients combine together in the presence of inevitable stochasticity in gene expression, to control the coupled fluctuations of gene expression that give rise to a one-dimensional developmental pattern in this organism.

Under prolonged nitrogen deprivation, one-dimensional filaments of the multicellular cyanobacterium Anabaena undergo a process of development, forming a pattern consisting of cells specialized for nitrogen fixation-heterocysts-, separated by a chain of about ten photosynthetic vegetative cells. The developmental program uses activation, inhibition, and transport to create spatial and temporal patterns of gene expression, in the presence of unavoidable stochastic fluctuations in gene expression among cells. Using a chromosomally-encoded fluorescent marker, we followed the expression of the important regulator HetR in individual cells along filaments, both under abundant nitrogen conditions as well as at different times after nitrogen deprivation. The results of our statistical analysis of these fluctuations illuminate the fundamental role that positive feedback, lateral inhibition and cell-cell communication play in the developmental program, not only after exposure to the external cue that triggers differentiation but also under non-inducing conditions. Furthermore our results establish the spatial extent to which gene expression is correlated along filaments.

[Effect of light and temperature on growth kinetics of Anabaena flosaquae under phosphorus limitation]

Phosphorus, light and temperature are the key environmental factors leading to algae growth. But the effects of interaction between light and temperature on the growth of Anabaena flosaquae under phosphorus limitation were not well documented in literature. Anabaena flosaquae was selected for the study and lab-scale experiment and simulation were carried out. The results showed that the optimal temperature of Anabaena flosaquae was 20 degrees C under phosphorus limitation when the light intensity was constant, and the optimal light intensity (illuminance) of Anabaena flosaquae was 3 000 lx under phosphorus limitation when the temperature was constant. Based on model fitting and parameter calibration, the optimal temperature and light intensity of Anabaena flosaquae were 21.03 degress C ± 1.55 degrees C and 2 675.12 lx ± 262.93 lx, respectively. These data were close to the actual water environmental condition at the end of spring. Results of this study will provide important foundation for prediction of Anabaena blooms.

Responses of a rice-field cyanobacterium Anabaena siamensis TISTR-8012 upon exposure to PAR and UV radiation

The effects of PAR and UV radiation and subsequent responses of certain antioxidant enzymatic and non-enzymatic defense systems were studied in a rice field cyanobacterium Anabaena siamensis TISTR 8012. UV radiation resulted in a decline in growth accompanied by a decrease in chlorophyll a and photosynthetic efficiency. Exposure of cells to UV radiation significantly affected the differentiation of vegetative cells into heterocysts or akinetes. UV-B radiation caused the fragmentation of the cyanobacterial filaments conceivably due to the observed oxidative stress. A significant increase of reactive oxygen species in vivo and DNA strand breaks were observed in UV-B exposed cells followed by those under UV-A and PAR radiation, respectively. The UV-induced oxidative damage was alleviated due to an induction of antioxidant enzymatic/non-enzymatic defense systems. In response to UV irradiation, the studied cyanobacterium exhibited a significant increase in antioxidative enzyme activities of superoxide dismutase, catalase and peroxidase. Moreover, the cyanobacterium also synthesized some UV-absorbing/screening substances. HPLC coupled with a PDA detector revealed the presence of three compounds with UV-absorption maxima at 326, 331 and 345 nm. The induction of the biosynthesis of these UV-absorbing compounds was found under both PAR and UV radiation, thus suggesting their possible function as an active photoprotectant.

Interspecific competition between Microcystis aeruginosa and Anabaena flos-aquae from Taihu Lake, China

Microcystis and Anabaena are the main cyanobacteria that cause cyanobacterial blooms in Taihu Lake, China. The mechanism of population competition between M. aeruginosa and A. flos-aquae was studied by co-cultivation in the laboratory. The growth of M. aeruginosa was inhibited, while the growth of A. flos-aquae was promoted. The degree of inhibition or promotion was related to the ratio of the initial cell densities. Both cell-free filtrates of A. flos-aquae and co-culture inhibited M. aeruginosa growth, while both cell-free filtrates of M. aeruginosa and co-culture promoted A. flos-aquae growth. Analysis of the cell-free filtrate by gas chromatography-mass spectrometry indicated that M. aeruginosa and A. flos-aquae may secrete some extracellular allelochemicals that inhibit (promote) the growth of M. aeruginosa (A. flos-aquae) in co-culture. These compounds included sulfur compounds, naphthalene derivatives, cedrene derivatives, quinones, phenol derivatives, diphenyl derivatives, anthracene derivatives, and phthalate esters. This study can help to understand the characteristics of M. aeruginosa and A. flos-aquae and to provide new concepts for the control of cyanobacterial blooms in Taihu Lake.

Impact of osmotic stress and temperature on pigments and proteins of Anabaena strains

A study on Anoboeno strains was carried out to investigate the effect of combined stress of polyethylene glycol 6000 (0,-5 bar and -7 bar) an d temperature (30 degreeC and 45 degreeC) onphotosynthetic pigments (chlorophyll a, carotenoids, phycobilins) and total proteins as stress metabolites. The selected strains, A. oryzoe and A. ellipsosporo were sensitive to osmotic stress at ambient temperature of 30 degreeC and increase in the temperature to 45 degreeC was harmful to the growth of Anoboeno strains. Chlorophyll a contents decreased at 30 degreeC and -7 bar pressure from 8.868 to 0.710 microg ml-1 and 4.360 to 0.220 microg ml-1 in A. oryzae and in A. ellipsospora, respectively and at -7 bar osmotic stress and 45 microC temperature, decrease in Chi a content of A.oryzae was 92.9%, however A. ellipsospora was highly sensitive and could not survive under these conditions. Carotenoids and phycobilins also showed decreasing trends with increase in temperature and osmotic potential. Moreover, combined stress adversely depleted the cellular activities leading to a marked decrease in total protein contents of the cell. A.oryzae and A.ellipsospora showed varying tolerance potential to osmotic and temperature stresses. The results indicated that A. ellipsospora was more sensitive towards these stresses in comparison to A.oryzoe.

Toxicity of five antibiotics and their mixtures towards photosynthetic aquatic organisms: implications for environmental risk assessment

The individual and combined toxicities of amoxicillin, erythromycin, levofloxacin, norfloxacin and tetracycline have been examined in two organisms representative of the aquatic environment, the cyanobacterium Anabaena CPB4337 as a target organism and the green alga Pseudokirchneriella subcapitata as a non-target organism. The cyanobacterium was more sensitive than the green alga to the toxic effect of antibiotics. Erythromycin was highly toxic for both organisms; tetracycline was more toxic to the green algae whereas the quinolones levofloxacin and norfloxacin were more toxic to the cyanobacterium than to the green alga. Amoxicillin also displayed toxicity to the cyanobacterium but showed no toxicity to the green alga. The toxicological interactions of antibiotics in the whole range of effect levels either in binary or multicomponent mixtures were analyzed using the Combination Index (CI) method. In most cases, synergism clearly predominated both for the green alga and the cyanobacterium. The CI method was compared with the classical models of additivity Concentration Addition (CA) and Independent Action (IA) finding that CI could accurately predict deviations from additivity. Risk assessment was performed by calculating the ratio between Measured Environmental Concentration (MEC) and the Predicted No Effect Concentration (PNEC). A MEC/PNEC ratio higher than 1 was found for the binary erythromycin and tetracycline mixture in wastewater effluents, a combination which showed a strong synergism at low effect levels in both organisms. From the tested antibiotic mixtures, it can be concluded that certain specific combinations may pose a potential ecological risk for aquatic ecosystems with the present environmentally measured concentrations.

Do high concentrations of microcystin prevent Daphnia control of phytoplankton?

Toxin-producing cyanobacteria have frequently been hypothesized to limit the ability of herbivorous zooplankton (such as Daphnia) to control phytoplankton biomass by inhibiting feeding, and in extreme cases, causing zooplankton mortality. Using limnocorral experiments in hyper-eutrophic ponds located in Alabama and Michigan (U.S.A.), we tested the hypothesis that high levels of cyanobacteria and microcystin, a class of hepatotoxins produced by several cyanobacterial genera, prevent Daphnia from strongly reducing phytoplankton abundance. At the start of the first experiment (Michigan), phytoplankton communities were dominated by toxic Microcystis and Anabaena (∼96% of total phytoplankton biomass), and concentrations of microcystin were ∼3 μg L⁻¹. Two weeks after adding Daphnia pulicaria from a nearby eutrophic lake, microcystin levels increased to ∼6.5 μg L⁻¹, yet Daphnia populations increased exponentially (r = 0.24 day⁻¹). By the third week, Daphnia had suppressed phytoplankton biomass by ∼74% relative to the no Daphnia controls and maintained reduced phytoplankton biomass until the conclusion of the five-week experiment. In the second experiment (Alabama), microcystin concentrations were greater than 100 μg L⁻¹, yet a mixture of three D. pulicaria clones from eutrophic lakes in southern MI increased and again reduced phytoplankton biomass, in this case by over 80%. The ability of Daphnia to increase in abundance and suppress phytoplankton biomass, despite high initial levels of cyanobacteria and microcystin, indicates that the latter does not prevent strong control of phytoplankton biomass by Daphnia genotypes that are adapted to environments with abundant cyanobacteria and associated cyanotoxins.

[Partial biological characteristics and algicidal activity of an algicidal bacterium]

An algicidal bacterium was isolated from freshwater (Lake Donghu in Wuhan) and coded as A01. The morphology of the algicidal bacterium was observed using optical microscope and electron microscopes, the results showed that A01 was rod-shaped, approximately 1.5 microm in length and 0.45 microm in width and with no flagella structure. A01 was Gram-negative and belongs to the family Acinetobacter sp. though identification by Gram's staining and 16S rDNA gene analysis. A01 exhibited strong algicidal activity on the bloom-forming cyanobacterium Anabaena eucompacta under laboratory conditions. The removal rate of chlorophyll a after 7-day incubation with the culture supernatant of A01 and thalli were 77% and 61%, respectively. Microscopic observation showed that almost all cyanobacterial cells were destroyed within 3 d of co-incubation with the supernatant of algicidal bacterium, but a mass of the cyanobacterial cell lysis was observed only after 5 d of co-incubation with the thalli of algicidal bacterium. These results indicated that the main algicidal component of A01 was in its culture supernatant. In other words, the strain A01 could secrete algicidal component against Anabaena eucompacta.

The susceptibility of five African Anopheles species to Anabaena PCC 7120 expressing Bacillus thuringiensis subsp. israelensis mosquitocidal cry genes

BACKGROUND

Malaria, one of the leading causes of death in Africa, is transmitted by the bite of an infected female Anopheles mosquito. Problems associated with the development of resistance to chemical insecticides and concerns about the non-target effects and persistence of chemical insecticides have prompted the development of environmentally friendly mosquito control agents. The aim of this study was to evaluate the larvicidal activity of a genetically engineered cyanobacterium, Anabaena PCC 7120#11, against five African Anopheles species in laboratory bioassays.

FINDINGS

There were significant differences in the susceptibility of the anopheline species to PCC 7120#11. The ranking of the larvicidal activity of PCC 7120#11 against species in the An. gambiae complex was: An. merus

CONCLUSIONS

PCC 7120#11 exhibited good larvicidal activity against larvae of the An. gambiae complex, but relatively weak larvicidal activity against An. funestus. The study has highlighted the importance of evaluating a novel mosquitocidal agent against a range of malaria vectors so as to obtain a clear understanding of the agent's spectrum of activity and potential as a vector control agent.

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Key Words

• malaria vectors
• anopheles
• bacillus thuringiensis subsp. israelensis
• cry proteins
• cyanobacteria
• anabaena sp. pcc 7120
• genetic engineering
• bioassays
• larvicidal activity

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MESH Headings

• Africa
• Anabaena/genetics
• Anabaena/growth & development
• Anabaena/metabolism
• Animals
• Anopheles/drug effects
• Anopheles/microbiology
• Anopheles/physiology
• Bacillus thuringiensis Toxins
• Bacterial Proteins/biosynthesis
• Bacterial Proteins/genetics
• Endotoxins/biosynthesis
• Endotoxins/genetics
• Female
• Hemolysin Proteins/biosynthesis
• Hemolysin Proteins/genetics
• Larva/drug effects
• Larva/microbiology
• Larva/physiology
• Mosquito Control/methods
• Pest Control, Biological/methods
• Survival Analysis

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Affiliation(s)

Irene Ketseoglou School of Molecular and Cell Biology, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa
Gustav Bouwer School of Molecular and Cell Biology, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa

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Chemoheterotrophic growth of the Cyanobacterium Anabaena sp. strain PCC 7120 dependent on a functional cytochrome c oxidase

Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium commonly used as a model organism for studying cyanobacterial cell differentiation and nitrogen fixation. For many decades, this cyanobacterium was considered an obligate photo-lithoautotroph. We now discovered that this strain is also capable of mixotrophic, photo-organoheterotrophic, and chemo-organoheterotrophic growth if high concentrations of fructose (at least 50 mM and up to 200 mM) are supplied. Glucose, a substrate used by some facultatively organoheterotrophic cyanobacteria, is not effective in Anabaena sp. PCC 7120. The gtr gene from Synechocystis sp. PCC 6803 encoding a glucose carrier was introduced into Anabaena sp. PCC 7120. Surprisingly, the new strain containing the gtr gene did not grow on glucose but was very sensitive to glucose, with a 5 mM concentration being lethal, whereas the wild-type strain tolerated 200 mM glucose. The Anabaena sp. PCC 7120 strain containing gtr can grow mixotrophically and photo-organoheterotrophically, but not chemo-organoheterotrophically with fructose. Anabaena sp. PCC 7120 contains five respiratory chains ending in five different respiratory terminal oxidases. One of these enzymes is a mitochondrial-type cytochrome c oxidase. As in almost all cyanobacteria, this enzyme is encoded by three adjacent genes called coxBAC1. When this locus was disrupted, the cells lost the capability for chemo-organoheterotrophic growth.

Impact of sonication at 20 kHz on Microcystis aeruginosa, Anabaena circinalis and Chlorella sp

Blooms of toxic cyanobacteria such as Microcystis aeruginosa periodically occur within wastewater treatment lagoons in the warmer months, and may consequently cause contamination of downstream water and outages of the supply of recycled wastewater. Lab-scale sonication (20 kHz) was conducted on suspensions of M. aeruginosa isolated from a wastewater treatment lagoon, and two other algal strains, Anabaena circinalis and Chlorella sp., to investigate cell reduction, growth inhibition, release of microcystin and sonication efficiency in controlling the growth of the M. aeruginosa. For M. aeruginosa, for all sonication intensities and exposure times trialled, sonication led to an immediate reduction in the population, the highest reduction rate occurring within the initial 5 min. Sonication for 5 min at 0.32 W/mL, or for a longer exposure time (>10 min) at a lower power intensity (0.043 W/mL), led to an immediate increase in microcystin level in the treated suspensions. However, prolonged exposure (>10 min) to sonication at higher power intensities reduced the microcystin concentration significantly. Under the same sonication conditions, the order of decreasing growth inhibition of the three algal species was: A. circinalis > M. aeruginosa > Chlorella sp., demonstrating sonication has the potential to selectively remove/deactivate harmful cyanobacteria from the algal communities in wastewater treatment lagoons.

[Effects of sediment on the growth of Microcystis and Anabaena in Yanghe reservoir]

Batch culture experiments were used to study the effect of leachate from sediment of Yanghe reservoir on the growth of Microcystis and Anabaena isolated from Yanghe reservoir. The results showed that the growth of Microcystis was significantly inhibited when the addition of anaerobic leachate from sediment in M11 culture medium was high (> or = 20% V/V). The maximum biomass of Microcystis was lower than that grown in pure M11 culture medium. But there was an obvious promotion on the growth of Anabaena when anaerobic leachate from sediment was added. The growth rate of Anabaena increased 36.6%, 47.2% and 36.0%, respectively, compared to M11 culture medium when adding 2%, 20% and 50% (V/V) anaerobic leachate. Compared to adding anaerobic leachate, aerobic leachate had no influence on the growth of Microcystis, while the growth rate of Anabaena was promoted by aerobic leachate. The growth rate of Anabaena increased 37.2% compared with M11 when adding 20% (V/V) of aerobic leachate. But after addition of Fe-citrate to the mixed culture medium (50% M11 culture medium +50% anaerobic leachate), the maximum biomass of Microcystis significantly increased. The results suggest that high organic matter concentration decreases iron availability for Microcystis.

FraH is required for reorganization of intracellular membranes during heterocyst differentiation in Anabaena sp. strain PCC 7120

In the filamentous, heterocyst-forming cyanobacteria, two different cell types, the CO(2)-fixing vegetative cells and the N(2)-fixing heterocysts, exchange nutrients and regulators for diazotrophic growth. In the model organism Anabaena sp. strain PCC 7120, inactivation of fraH produces filament fragmentation under conditions of combined nitrogen deprivation, releasing numerous isolated heterocysts. Transmission electron microscopy of samples prepared by either high-pressure cryo-fixation or chemical fixation showed that the heterocysts of a ΔfraH mutant lack the intracellular membrane system structured close to the heterocyst poles, known as the honeycomb, that is characteristic of wild-type heterocysts. Using a green fluorescent protein translational fusion to the carboxyl terminus of FraH (FraH-C-GFP), confocal microscopy showed spots of fluorescence located at the periphery of the vegetative cells in filaments grown in the presence of nitrate. After incubation in the absence of combined nitrogen, localization of FraH-C-GFP changed substantially, and the GFP fluorescence was conspicuously located at the cell poles in the heterocysts. Fluorescence microscopy and deconvolution of images showed that GFP fluorescence originated mainly from the region next to the cyanophycin plug present at the heterocyst poles. Intercellular transfer of the fluorescent tracers calcein (622 Da) and 5-carboxyfluorescein (374 Da) was either not impaired or only partially impaired in the ΔfraH mutant, suggesting that FraH is not important for intercellular molecular exchange. Location of FraH close to the honeycomb membrane structure and lack of such structure in the ΔfraH mutant suggest a role of FraH in reorganization of intracellular membranes, which may involve generation of new membranes, during heterocyst differentiation.

Nitrogen status dependent oxidative stress tolerance conferred by overexpression of MnSOD and FeSOD proteins in Anabaena sp. strain PCC7120

The heterocystous nitrogen-fixing cyanobacterium, Anabaena sp. strain PCC7120 displayed two superoxide dismutase (SOD) activities, namely FeSOD and MnSOD. Prolonged exposure of Anabaena PCC7120 cells to methyl viologen mediated oxidative stress resulted in loss of both SOD activities and induced cell lysis. The two SOD proteins were individually overexpressed constitutively in Anabaena PCC7120, by genetic manipulation. Under nitrogen-fixing conditions, overexpression of MnSOD (sodA) enhanced oxidative stress tolerance, while FeSOD (sodB) overexpression was detrimental. Under nitrogen supplemented conditions, overexpression of either SOD protein, especially FeSOD, conferred significant tolerance against oxidative stress. The results demonstrate a nitrogen status-dependent protective role of individual superoxide dismutases in Anabaena PCC7120 during oxidative stress.

Effects of carbaryl and 1-naphthol on soil population of cyanobacteria and microalgae and select cultures of diazotrophic cyanobacteria

Carbaryl application to soil collected from a rice fallow field was relatively less toxic to viable estimates of cyanobacteria and microalgae under nonflooded conditions than under flooded conditions. Application of 1-naphthol, the hydrolysis product of carbaryl, to soil under both the regimes increased the population of both cyanobacteria and microalgae. Soil application of carbaryl and 1-naphthol in combination, up to 1.0 kg ha(-1), was nontoxic to the viable population. The toxicity exerted by carbaryl and 1-naphthol towards growth, measured in terms of chlorophyll a, and nitrogenase activity was more pronounced in Anabaena spp. than in Nostoc spp.

[Influence of nutrient sources on Anabaena spiroides growth and odorous compounds production characteristics]

The occurrence of taste and odors, produced by secondary metabolites of cyanobacteria, has been one of the major water quality problems in drinking water. However, the odorous compounds produced by cyanobacteria usually differ significantly with different species. One cyanobacterium isolated from Yanghe reservoir was identified as Anabaena sp., which can produce high level of geosmin consistently during laboratory culture. By culture expanding experiments, the algal growth and geosmin production characteristics of the Anabaena sp. were studied on different conditions of nitrogen and phosphorus sources. The results indicated that geosmin mainly remained in the intracellular algal cells regardless of the nutrient sources, and the extracellular content was only in th range of 0.2% - 9.6%. Compared with ammonia nitrogen conditions, the growth of Anabaena sp. in nitrate nitrogen conditions was much higher, with a 1.4-fold variation in geosmin production. While ammonia nitrogen concentration was 0.5 mg/L, the algal biomass and geosmin production achieved the highest level of 3.8 x 10(4) cells, mL(-1) and 1.1 x 10(4) ngL(-1), respectively. When the nitrate nitrogen concentration was 2.0 mg/L, the algal biomass and geosmin production achieved the highest level of 6.6 x 10(4) cells x mL(-1) and 1.3 x 10(4) ng x L(-1), respectively. Compared with nitrogen sources, the growth of Anabaena sp. could be promoted significantly until phosphorus level attained 0.12 mg/L, indicating that phosphorus is the main limiting nutrient source for Anabaena sp.. For Yanghe reservoir, the nutrient level has already been enough for the growth of Anabaena sp. Therefore, the nutrient source content, especially phosphorus, should be reduced effectively to control the cyanobacterium bloom and taste and odor problems.

Inhibition of the growth of two blue-green algae species (Microsystis aruginosa and Anabaena spiroides) by acidification treatments using carbon dioxide

The effect of pH adjusted by aeration with carbon dioxide (CO(2)) on the growth of two species of blue-green algae, Microcystis aeruginosa and Anabaena spiroides, was investigated. Three conditions (pH 5.5, 6.0 and 6.5) were found to have significant inhibitory effects on the growth of the two algae species when acidification treatment was conducted during the logarithmic phase. Differences in the inhibition effect of acidification existed between the two species algae. The tolerance of M. aeruginosa to these conditions was also investigated. The results indicated that M. aeruginosa was inhibited significantly, but not dead at pH 6.5, whereas death occurred at pH 5.5 and 6.0. The greatest inhibitory effect of acidification treatment conducted during the stable breeding phase of M. aeruginosa occurred at pH 5.5, while no inhibitory effect was found at pH 6.5.

Utilization of the cyanobacteria Anabaena sp. CH1 in biological carbon dioxide mitigation processes

Before switching totally to alternative fuel stage, CO(2) mitigation process has considered a transitional strategy for combustion of fossil fuels inevitably. In comparison to other CO(2) mitigation options, such as oceanic or geologic injection, the biological photosynthetic process would present a far superior and sustainable solution under both environmental and social considerations. The utilization of the cyanobacteria Anabaena sp. CH1 in carbon dioxide mitigation processes is analyzed in our research. It was found that an original developed photobioreactor with internal light source exhibits high light utilization. Anabaena sp. CH1 demonstrates excellent CO(2) tolerance even at 15% CO(2) level. This enables flue gas from power plant to be directly introduced to Anabaena sp. CH1 culture. Double light intensity and increased 47% CO(2) bubble retention time could enhance CO(2) removal efficiencies by 79% and 67%, respectively. A maximum CO(2) fixation rate of 1.01 g CO(2)L(-1)day(-1) was measured experimentally.

Role of the all1549 (ana-rsh) gene, a relA/spoT homolog, of the Cyanobacterium Anabaena sp. PCC7120

The role of a single relA/spoT homolog all1549 (designated hereafter as ana-rsh) of the cyanobacterium Anabaena sp. PCC7120 was investigated. The complementation test in Escherichia coli showed that the protein encoded by ana-rsh possesses guanosine tetraphosphate (p)ppGpp-synthase/hydrolase activity. Under laboratory growth conditions, a low level of ppGpp was detected in Anabaena sp. PCC7120 and the loss of ana-rsh was lethal. Amino acid starvation induced ppGpp accumulation to an appropriate level, and nitrogen deficiency did not alter the ppGpp concentration in Anabaena cells. These data suggest that ana-rsh is required for cell viability under normal growth conditions and involved in the (p)ppGpp-related stringent response to amino acid deprivation, but not related to heterocyst formation and nitrogen fixation of Anabaena sp. PCC7120.

The sigE gene is required for normal expression of heterocyst-specific genes in Anabaena sp. strain PCC 7120

The filamentous cyanobacterium Anabaena (Nostoc) sp. strain PCC 7120 produces specialized cells for nitrogen fixation called heterocysts. Previous work showed that the group 2 sigma factor sigE (alr4249; previously called sigF) is upregulated in differentiating heterocysts 16 h after nitrogen step-down. We now show that the sigE gene is required for normal heterocyst development and normal expression levels of several heterocyst-specific genes. Mobility shift assays showed that the transcription factor NtcA binds to sites in the upstream region of sigE and that this binding is enhanced by 2-oxoglutarate (2-OG). Deletions of the region containing the NtcA binding sites in P(sigE)-gfp reporter plasmids showed that the sites contribute to normal developmental regulation but are not essential for upregulation in heterocysts. Northern RNA blot analysis of nifH mRNA revealed delayed and reduced transcript levels during heterocyst differentiation in a sigE mutant background. Quantitative reverse transcription-PCR (qRT-PCR) analyses of the sigE mutant showed lower levels of transcripts for nifH, fdxH, and hglE2 but normal levels for hupL. We developed a P(nifHD)-gfp reporter construct that showed strong heterocyst-specific expression. Time-lapse microscopy of the P(nifHD)-gfp reporter in a sigE mutant background showed delayed development and undetectable green fluorescent protein (GFP) fluorescence. Overexpression of sigE caused accelerated heterocyst development, an increased heterocyst frequency, and premature expression of GFP fluorescence from the P(nifHD)-gfp reporter.

A coagulation-powdered activated carbon-ultrafiltration--multiple barrier approach for removing toxins from two Australian cyanobacterial blooms

Cyanobacteria are a major problem for the world wide water industry as they can produce metabolites toxic to humans in addition to taste and odour compounds that make drinking water aesthetically displeasing. Removal of cyanobacterial toxins from drinking water is important to avoid serious illness in consumers. This objective can be confidently achieved through the application of the multiple barrier approach to drinking water quality and safety. In this study the use of a multiple barrier approach incorporating coagulation, powdered activated carbon (PAC) and ultrafiltration (UF) was investigated for the removal of intracellular and extracellular cyanobacterial toxins from two naturally occurring blooms in South Australia. Also investigated was the impact of these treatments on the UF flux. In this multibarrier approach, coagulation was used to remove the cells and thus the intracellular toxin while PAC was used for extracellular toxin adsorption and finally the UF was used for floc, PAC and cell removal. Cyanobacterial cells were completely removed using the UF membrane alone and when used in conjunction with coagulation. Extracellular toxins were removed to varying degrees by PAC addition. UF flux deteriorated dramatically during a trial with a very high cell concentration; however, the flux was improved by coagulation and PAC addition.

Effects of monosulfuron on growth, photosynthesis, and nitrogenase activity of three nitrogen-fixing cyanobacteria

Application of monosulfuron, a new sulfonylurea herbicide, produced a simulative effect on heterocyst formation and nitrogenase activity but an inhibitory effect on photosynthesis, i.e., a lower net photosynthetic rate, fewer photosynthetic pigments, and a smaller Fv/Fm ratio at increasingly higher monosulfuron concentrations (0.001-10 mg/l) for three nonspecific filamentous nitrogen-fixing cyanobacteria: Anabaena azollae, A. flos-aquae, and A. azotica. The decrease in biliprotein of algal cells was less than that of carotenoid and chlorophyll-a. Monosulfuron was more readily degraded and less accumulated in A. azotica compared with A. azollae and A. flos-aquae. The three algae exhibited varying degrees of sensitivity to monosulfuron: Calculated 50% inhibition concentrations (IC(50)s) of algal growth and no observed-effect concentration (NOEC) values after 4 days of treatment were 0.014 and 0.005, 0.029 and 0.019, and 0.22 and 0.075 mg/l for A. flos-aquae, A. azollae, and A. azotica, respectively. Normal agricultural use of monosulfuron at postemergence rates of 0.3-0.8 mg/l in rice fields will likely be toxic to these three ubiquitous nitrogen-fixing cyanobacteria. Low-dose monosulfuron application (<0.1 mg/l) enables growth of the more tolerant A. azotica as biofertilizer, and the use of photosynthetic efficiency and growth rates as sensitive-indicator indexes of toxicity to nitrogen-fixing cyanobacteria are recommended.

Integrated membrane systems incorporating coagulation, activated carbon and ultrafiltration for the removal of toxic cyanobacterial metabolites from Anabaena circinalis

The use of integrated membrane systems (a train of treatment processes incorporating one or more membranes) is increasing globally as the technology is very effective for the production of high quality drinking water. In this investigation a laboratory scale integrated membrane system (IMS) featuring coagulation, powdered activated carbon (PAC) and ultrafiltration (UF) was investigated for the removal of an Australian strain of the cyanobacteria Anabaena circinalis and the cyanotoxin it produced. Three coagulants were compared, aluminium chlorohydrate (ACH), aluminium sulphate (alum) and an engineered aluminium coagulant referred to as high performance aluminium chlorohydrate (HPAC). PAC (Acticarb PS1000) was tested to determine adsorption of extracellular saxitoxin. Removal of A. circinalis cells was 100% by UF alone and the removal of cells prior to the membrane by coagulation reduced fouling attributed to algogenic organic material. Alum was the least efficient coagulant for removal of cells while ACH and HPAC were similar. Saxitoxin removal reached a maximum of 80% using ACH and PAC. The UF-IMS was challenged using a natural bloom of A. circinalis that occurred in the Myponga Reservoir in South Australia.

Inhibition of nitrogen-fixing activity of the cyanobiont affects the localization of glutamine synthetase in hair cells of Azolla

In the Azolla-Anabaena association, the host plant Azolla efficiently incorporates and assimilates ammonium ions that are released from the nitrogen-fixing cyanobiont, probably via glutamine synthetase (GS; EC 6.3.1.2) in hair cells, which are specialized cells protruding into the leaf cavity. In order to clarify the regulatory mechanism underlying ammonium assimilation in the Azolla-Anabaena association, Azolla plants were grown under an argon environment (Ar), in which the nitrogen-fixing activity of the cyanobiont was inhibited specifically and completely. The localization of GS in hair cells was determined by immunoelectron microscopy and quantitative analysis of immunogold labeling. Azolla plants grew healthily under Ar when nitrogen sources, such as NO(3)(-) and NH(4)(+), were provided in the growth medium. Both the number of cyanobacterial cells per leaf and the heterocyst frequency of the plants under Ar were similar to those of plants in a nitrogen environment (N(2)). In hair cells of plants grown under Ar, regardless of the type of nitrogen source provided, only weak labeling of GS was observed in the cytoplasm and in chloroplasts. In contrast, in hair cells of plants grown under N(2), abundant labeling of GS was observed in both sites. These findings indicate that specific inhibition of the nitrogen-fixing activity of the cyanobiont affects the localization of GS isoenzymes. Ammonium fixed and released by the cyanobiont could stimulate GS synthesis in hair cells. Simultaneously, the abundant GS, probably GS1, in these cells, could assimilate ammonium rapidly.

Effect of pH, EDTA, and anions on heavy metal toxicity toward a bioluminescent cyanobacterial bioreporter

The bioavailability and therefore toxicity of a metal depends on the chemical species present in a particular environment. We evaluated the effect of a series of factors that could potentially modify metal speciation on the toxicity of Hg, Cu, Zn, and Cd toward a recombinant strain of the freshwater cyanobacterium Anabaena sp. PCC 7120 with cloned lux operon of luminescent terrestrial bacterium Photorhabdus luminescens. The strain, denoted as Anabaena CPB4337, showed a high constitutive luminescence with no need to add exogenous aldehyde. The tested factors were pH, EDTA (as organic ligand), and anions PO(4)(3-), CO(3)(2-), and Cl(-). Chemical modeling and correlation analyses were used to predict metal speciation and link it with toxicity. In general, metal toxicity significantly correlated to the predicted metal free-ion concentration, although Zn-EDTA complexes and certain Hg chloro-complexes could also exhibit some toxicity to cyanobacteria. An interesting feature of metal toxicity to strain Anabaena CPB4337 was that low amounts of PO(4)(3-) and CO(3)(2-) increased metal toxicity; this effect could not be related to significant changes in metal speciation and could be attributed to a modulating effect of these anions on metal/uptake toxicity. The combination of toxicity studies that take into account a range of factors that might modulate metal toxicity with chemical modeling to predict changes in metal speciation might be useful for interpreting complex toxicity data. Finally, this cyanobacterial bioreporter, due to its ecological relevance as a primary producer, could be used as a tool for toxicity assessment in freshwater environments.

Responses of cyanobacterium Anabaena doliolum during nickel stress

Growth and biochemical responses of heterocystous nitrogen fixing cyanobacteria Anabaena doliolum were studied upon exposure to various concentrations of nickel (0.1 to 100 microM) for duration of up to 4 days, in view of its tolerance. The growth of the cyanobacterium was increased in terms of cell density (O.D), heterocyst frequency chlorophyll-a, carotenoid and c-phycocynin up to moderate exposure (10 microM for 96 hr of Ni treatment). Protein and total non protein thiol were measured as stress responsive metabolites and frequency of heterocyst and spores were observed in responses to Ni. The present study demonstrated that the tested cyanobacterium exhibited dose specific responses of metal towards studied different morphological, physiological and biochemical parameters.