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.

Transcript levels of rbcR1, ntcA, and rbcL/S genes in cyanobacterium Anabaena sp. PCC 7120 are downregulated in response to cold and osmotic stress

Using differential display, we identified the Anabaena sp. PCC 7120 ribulose 1,5-bisphosphate carboxylase transcriptional regulator (rbcR1) gene, a member of the LysR family of positive transcription factors. The rbcR1 transcript and its putative target gene ribulose 1,5-bisphosphate carboxylase/oxygenase (rbcL/S) were repressed by cold (20 degrees C) and osmotic (sucrose and salt) stress. Cold stress also induced a transient downregulation of the Anabaena 7120 ntcA transcriptional regulator. Expression of the ntcA gene, however, returned to normal levels 2 h after initiation of cold stress and increased significantly above normal levels 24 h after growth at 20 degrees C. The early decline in the expression of the ntcA, rbcR1, and rbcL/S transcripts appears to be part of the Anabaena 7120 global adaptation response to stress. The substantial increase in the ntcA gene expression 24 h following cold stress suggests that Anabaena 7120 experiences substantial nitrogen limitation under these conditions. These data suggest that in response to stress, Anabaena 7120 decreases its metabolic activity through regulation of the CO(2) fixation machinery while enhancing its nitrogen assimilation by inducing the expression of the nitrogen global transcriptional regulator, NtcA.

NaCl-induced oxidative damage in the cyanobacterium Anabaena doliolum

Results obtained with graded concentrations of NaCl (20-200 m M) show decrease in the chlorophyll 'a' contents of Anabaena with increasing concentration of NaCl except at extremely low concentration of NaCl (5-20 m M). The rate of Hill activity and oxygen evolution are found to be stimulated by lower concentrations of NaCl, but not at higher concentrations of NaCl. Results have demonstrated that the O(2) evolution process is relatively more sensitive to NaCl stress than the Hill activity. Further, the results show NaCl induced an increase in the rate of RNO bleaching and loss of total thiol (-SH) contents. Taken together, these results suggest a NaCl-induced general oxidative stress. Results on the effect of oxygen radical quenchers reveal a predominant role of singlet oxygen in the NaCl-induced general oxidative stress as evident from a higher quenching effect of sodium azide than formate and histidine on the rate of RNO bleaching in Anabaena cells. However, the rate of lipid peroxidation and SOD activity show a declining pattern in response to increasing concentrations of NaCl. There is the possibility of a NaCl-induced decrease in the rate of lipid peroxidation when the SOD activity is also lower. But the NaCl-induced decline in the SOD activity does suggest that symptoms of general oxidative stress at elevated levels of NaCl are apparently owing to collapse of intracellular defense of the cells against the toxic oxygen radicals, not because of the higher rate of photosynthetic activity.

Spiroidesin, a novel lipopeptide from the cyanobacterium Anabaena spiroides that inhibits cell growth of the cyanobacterium Microcystis aeruginosa

Spiroidesin (1), a novel D-amino acid-containing linear lipopeptide, was isolated from waterblooms of the cyanobacterium Anabaena spiroides. The structure was identified by 2D NMR and chemical degradation analyses. Spiroidesin inhibited cell growth of the toxic cyanobacterium Microcystis aeruginosa (IC(50), 1.6 x 10(-6) M).

UV-B-induced formation of reactive oxygen species and oxidative damage of the cyanobacterium Anabaena sp.: protective effects of ascorbic acid and N-acetyl-L-cysteine

Reactive oxygen species (ROS) are involved in the oxidative damage of the cyanobacterium Anabaena sp. caused by UV-B (280-315 nm) radiation. UV-B-induced overproduction of ROS as well as the oxidative stress was detected in vivo by using the ROS-sensitive probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). Thiobarbituric acid reactive substances (TBARS) and fluorometric analysis of DNA unwinding (FADU) methods were adapted to measure lipid peroxidation and DNA strand breaks in Anabaena sp. Moderate UV-B radiation causes an increase of ROS production, enhanced lipid peroxidation and DNA strand breaks, yielding a significantly decreased survival. In contrast, the supplementation of UV-A in our work only showed a significant increase in total ROS levels and DNA strand breaks while no significant effect on lipid peroxidation, chlorophyll bleaching or survival was observed. The presence of ascorbic acid and N-acetyl-L-cysteine (NAC) reversed the oxidative stress and protected the organisms from chlorophyll bleaching and the damage of photosynthetic apparatus induced by UV-B significantly, resulting in a considerably higher survival rate. Ascorbic acid also exhibited a significant protective effect on lipid peroxidation and DNA strand breaks while NAC did not show a substantial effect. These results suggest that ascorbic acid exhibited significantly higher protective efficiency with respect to DNA strand breaks and survival than NAC while NAC appears to be especially effective in defending the photosynthetic apparatus from oxidative damage.

Involvement of reactive oxygen species in the UV-B damage to the cyanobacterium Anabaena sp

Reactive oxygen species (ROS) are involved the damage of living organisms under environmental stress including UV radiation. Cyanobacteria, photoautotrophic prokaryotic organisms, also suffer from increasing UV-B due to the depletion of the stratospheric ozone layer. The increased UV-B induces the production of ROS in vivo detected by using the ROS-sensitive probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). Ascorbic acid and N-acetyl-L-cysteine (NAC) scavenged ROS effectively, while alpha-tocopherol acetate or pyrrolidine dithiocarbamate (PDTC) did not. The presence of rose bengal and hypocrellin A increased the ROS level by photodynamic action in the visible light. The presence of the herbicide, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), increased ROS production slightly, and ROS formation was greatly enhanced by the addition of methyl viologen due to the fact that this redox system diverts electrons from PSI to oxygen and thus forms ROS. UV-B induces ROS generation by photodynamic action and inhibition of the electron transport by damaging the electron receptors or enzymes associated with the electron transport chain during photosynthesis.

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.

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.

Hydrogen peroxide inhibits photosynthetic electron transport in cells of cyanobacteria

The effect of H2O2 on photosynthetic O2 evolution and photosynthetic electron transfer in cells of cyanobacteria Anabaena variabilis and Anacystis nidulans was studied. The following experiments were performed: 1) directly testing the effect of exogenous H2O2; 2) testing the effect of intracellular H2O2 generated with the use of methyl viologen (MV); 3) testing the effect of inhibiting intracellular H2O2 decomposition by salicylic acid (SA) and 3-amino-1,2,4-triazole (AT). H2O2 inhibited photosynthetic O2 evolution and light-induced reduction of p-benzoquinone (BQ) + ferricyanide (FeCy) in the Hill reaction. The I50 value for H2O2 was ~0.75 mM. Photosynthetic electron transfer in the cells treated with H2O2 was not maintained by H2O2, NH2OH, 1,5-diphenylcarbazide, tetraphenylboron, or butylated hydroxytoluene added as artificial electron donors for Photosystem (PS) II. The H2O --> CO2, H2O --> MV (involving PSII and PSI) and H2O --> BQ + FeCy (chiefly dependent on PSII) electron transfer reactions were inhibited upon incubation of the cells with MV, SA, or AT. The N,N,N,N-tetramethyl-p-phenylenediamine --> MV (chiefly dependent on PSI) electron transfer was inhibited by SA and AT but was resistant to MV. The results show that H2O2 inhibits photosynthetic electron transfer. It is unlikely that H2O2 could be a physiological electron donor in oxygenic photosynthesis.

Nostocyclamide M: a cyanobacterial cyclic peptide with allelopathic activity from Nostoc 31

A cyclic peptide containing thiazole and oxazole moieties was isolated from Nostoc 31 and its structure determined by chemical degradation detailed NMR and mass spectroscopic analyses. The compound is stereochemically pure and closely related to nostocyclamide in which D-valine is replaced by D-methionine. Therefore, it differs from tenuecyclamide C reported to contain L-methionine. It shows allelopathic activity against Anabaena 7120, but is inactive against grazers.

Isolation and characterization of transposon-induced chlorate resistant mutants of the cyanobacterium Anabaena species PCC 7120

Mutants of Anabaena sp. PCC 7120 resistant to chlorate were isolated using transposon mutagenesis. The Anabaena population of 5 x 10(7) cells ml(-1) and log phase Escherichia coli cultures in undisturbed conditions produced maximum exconjugants. Nitrate-promoted growth and cellular constituents observed in the parent were absent in the mutants. Nitrate repressed heterocyst formation and N2-fixation in the parent, but had little or no effect on the mutants.

Isolation and characterization of the thylakoid membranes from the NaCl-resistant (NaCl(r)) mutant strain of the cyanobacterium Anabaena variabilis

NaCl-induced changes in the thylakoid membrane of wild-type Anabaena variabilis and its NaCl(r) mutant strain have been studied. Biochemical characterization of the thylakoid membrane was done by taking its absorption and fluorescence spectra at different wavelength. The thylakoid membranes of both strains were isolated by mechanical disruption of the freeze-dried and lysozyme-treated cells, followed by differential and density gradient centrifugation. The light absorption spectra of the thylakoid membrane showed three and two peaks in NaCl(r) mutant strain and its wild-type counterpart respectively at wavelengths of 400-850 nm. These peaks revealed that the thylakoid membrane contains a large amount of carotenoid and chlorophyll a. Fluorescence emission spectra of thylakoid membrane of NaCl(r) mutant and its wild-type strain at excitation wavelength of 335 nm showed two different peaks, one at 340 nm and the other at 663 nm respectively. The light absorption and fluorescence spectra of the thylakoid membrane also revealed that the membrane contained carotenoid pigment, chlorophyll (Chl) a, and a pigment with an emission peak at 335 nm. The HPLC analysis of the pigments of the thylakoid membrane indicates that the NaCl(r) mutant strain under NaCl stress contained an additional peak for the carotenoid pigment, which was lacking in its wild-type counterpart. The major peak in thylakoid membrane was that of echinenone and beta-carotene. Whereas the polypeptide composition of thylakoid membrane differed in the wild-type and its NaCl(r) mutant strain, no difference in the cell wall protein pattern was observed in both strains. The thylakoid membrane of NaCl(r) mutant strain contained two additional protein bands that were absent in its wild-type counterpart. The thylakoid membrane of the wild-type and its NaCl(r) mutant strain also showed morphological variations under NaCl stress.

Antimicrobial action of exogenous chitosan

The objective of this chapter is to present fundamental factors (e.g. intrinsic and extrinsic) influencing chitosan as antimicrobial agent, for effective practical application. The antimicrobial activity of chitosan is well observed on a wide variety of micro-organisms including fungi, algae and some bacteria. However, the antimicrobial action is influenced by intrinsic and extrinsic factors such as the type of chitosan (e.g. plain or derivative); degree of chitosan polymerization; host natural nutrient constituency; substrate chemical and/or nutrient composition; and environmental conditions (e.g. substrate water activity (Aw) and/or moisture). Although both plain and derivative chitosans are effective as antimicrobial agents, there is a differential effect between them. Their differential antimicrobial effect is mainly exhibited in live host plants; thus the antifungal effect of N-carboxymethyl chitosan (NCMC) is different in vegetable as compared with graminea host. At the same time, pentamer and heptamer chitosan units seem to have better antifungal action than larger units. Chitosan antimicrobial action is more immediate on fungi and algae, followed by bacteria; the chitosan site of action is at the microbial cell wall.

Regulation of cold shock-induced RNA helicase gene expression in the Cyanobacterium anabaena sp. strain PCC 7120

Expression of the Anabaena sp. strain PCC 7120 RNA helicase gene crhC is induced by cold shock. crhC transcripts are not detectable at 30 degrees C but accumulate at 20 degrees C, and levels remain elevated for the duration of the cold stress. Light-derived metabolic capability, and not light per se, is required for crhC transcript accumulation. Enhanced crhC mRNA stability contributes significantly to the accumulation of crhC transcripts, with the crhC half-life increasing sixfold at 20 degrees C. The accumulation is reversible, with the cells responding more rapidly to temperature downshifts than to upshifts, as a result of the lack of active mRNA destabilization and the continuation of crhC transcription, at least transiently, after a temperature upshift. Translational inhibitors do not induce crhC expression to cold shock levels, indicating that inhibition of translation is only one of the signals required to activate the cold shock response in Anabaena. Limited amounts of protein synthesis are required for the cold shock-induced accumulation of crhC transcripts, as normal levels of accumulation occur in the presence of tetracycline but are abolished by chloramphenicol. Regulation of crhC expression may also extend to the translational level, as CrhC protein levels do not correlate completely with the pattern of mRNA transcript accumulation. Our experiments indicate that the regulation of crhC transcript accumulation is tightly controlled by both temperature and metabolic activity at the levels of transcription, mRNA stabilization, and translation.

Studies on nitric oxide (NO) formation by the green alga Scenedesmus obliquus and the diazotrophic cyanobacterium Anabaena doliolum

This study provides preliminary evidence that NO production could be a general attribute of algae. Anabaena doliolum was found to be a better NO producer than Scenedesmus and Synechoccocus. Experiments conducted with inhibitors of photosynthesis (DCMU), ATP synthesis (DCCD), and the uncoupler (2,4-DNP) and its analog arsenate clearly revealed that inhibition of nitrite assimilation through the blockage of nitrite reductase (NiR) is primarily responsible for NO emission. A linear relationship between nitrite concentration in the culture medium and NO in the exhaust gas supports the view that accumulation of nitrite is responsible for NO formation. A failure of Scenedesmus, grown in the medium substituted with W for Mo, to produce either NO/NO-2 in light or a 'light-off' peak, and a resumption of these activities upon the addition of Mo proved beyond doubt that a functional nitrate reductase (NR) is necessary for the production of nitrite and NO by algae grown on nitrate as the nitrogen source. Moreover, the appearance of a NO peak immediately after nitrite supplementation under dark conditions in W-substituted cultures with or without glucose ruled out an enzymatic role of NR in NO emission.

Response of the paddy field cyanobacterium Anabaena doliolum to carbofuran

Assessment of the influence of carbofuran on the nontarget cyanobacterium Anabaena doliolum revealed that this sheathless heterocystous form of cyanobacteria was more sensitive to the insecticide carbofuran. Anabaena doliolum was initially able to utilize low concentrations of carbofuran, whereas higher concentrations and the subsequent formation of hydrolytic breakdown products were toxic. Growth inhibition reached more than 50% by treatment with 80 and 100 ppm of the insecticide. Nitrogenase activity of the cyanobacterium was reduced by 38% after 48 h by treatment with 100 ppm carbofuran with no observed change in heterocyst frequency. Toxicity of the insecticide was the highest at pH 4-6 (46-59%) and the lowest at pH 7-10 (12-27%) due to the persistence of carbofuran and the resulting alkaline-catalyzed hydrolysis associated with the water regime of the rice fields. Doubling the initial population level of the cyanobacterium reduced the toxicity of the insecticide.

Pleiotropic effects of potassium deficiency in a heterocystous, nitrogen-fixing cyanobacterium, Anabaena torulosa

Omission of potassium from the growth medium caused multiple metabolic impairments and resulted in cessation of growth of the filamentous, heterocystous, nitrogen-fixing cyanobacterium Anabaena torulosa, during both diazotrophic and nitrogen-supplemented growth. Prominent defects observed during potassium deprivation were: (i) the loss of photosynthetic pigments, (ii) impairment of photosynthetic functions, (iii) reduced synthesis of dinitrogenase reductase (Fe-protein), (iv) inhibition of nitrogenase activity, and (v) specific qualitative modifications of protein synthesis leading to the repression of twelve polypeptides and synthesis and accumulation of nine novel polypeptides. The observed metabolic defects were reversible, and growth arrested under prolonged potassium deficiency was fully restored upon re-addition of potassium. Such pleiotropic effects of potassium deficiency demonstrate that apart from its well-known requirement for pH and turgor homeostasis, K+ plays other vital specific roles in cyanobacterial growth and metabolism.

Expression of the mouse metallothionein-I gene conferring cadmium resistance in a transgenic cyanobacterium

This paper reports the construction of a transgenic strain of cyanobacterium aimed at removing heavy metal pollution in waters. The mouse metallothionein-I (mMT-I) gene was inserted in the vector pRL-439 downstream of the strong psbA promoter. The resulting plasmid pRL-MT was ligated at the EcoRI site of the shuttle vector pKT-210 to generate the shuttle expression vector pKT-MT. This recombinant plasmid was introduced into Anabaena sp. PCC 7120 by triparental conjugative transfer. After selection on streptomycin, a stable transgenic Anabaena strain was obtained. The presence of the mMT-I gene was confirmed by DNA/DNA hybridization and its expression was demonstrated by immunodetection with specific antibodies. A metal tolerance experiment showed that this transgenic Anabaena strain had acquired higher metal resistance.

Effects of the herbicide molinate on mixotrophic growth, photosynthetic pigments, and protein content of Anabaena sphaerica under different light conditions

The effects of the carbamate herbicide molinate on growth and chlorophyll a, biliprotein, and protein content of the nitrogen-fixing cyanobacterium Anabaena sphaerica grown mixotrophically under 3000- and 300-lux light intensity were studied. Under two light intensities, the three concentrations of molinate tested (5, 25, and 50 microg ml-1) can significantly inhibit algal growth in a dose-dependent manner. The high concentration of molinate (50 microg ml-1) stimulated the synthesis of chlorophyll a and protein, but inhibited the formation of biliprotein, and these effects appear to be greater at 3000 lux than at 300 lux. The effects of the other two concentrations of molinate (5 and 25 microg ml-1) on chlorophyll a and biliprotein varied with time, but 5 microg ml-1 molinate had an inhibitory effect on the synthesis of protein. It was demonstrated that different concentrations of molinate had different effects on chlorophyll a, biliprotein, and protein content, which varied with light intensity. The results support the suggestion that the physiological mode of molinate toxicity to A. sphaerica is related to its interference with the metabolism of protein, particularly the formation and functional effectiveness of some special protein.

Dechlorination of lindane by the cyanobacterium Anabaena sp. strain PCC7120 depends on the function of the nir operon

Nitrate is essential for lindane dechlorination by the cyanobacteria Anabaena sp. strain PCC7120 and Nostoc ellipsosporum, as it is for dechlorination of other organic compounds by heterotrophic microorganisms. Based on analyses of mutants and effects of environmental factors, we conclude that lindane dechlorination by Anabaena sp. requires a functional nir operon that encodes the enzymes for nitrate utilization.

Copper-induced changes in the urea uptake and urease activity in the cyanobacteria Anabaena doliolum and Anacystis nidulans: interaction with sulphur containing amino acids

Copper-induced changes in the urea uptake and urease activity have been investigated in the cyanobacteria Anabaena doliolum and Anacystis nidulans. Copper, at and above 5 mumol/L concentration, inhibited urea uptake and urease activity systems in both the cyanobacteria in a concentration dependent manner. However, the urea uptake and urease activity systems in A. nidulans appeared slightly more tolerant to copper than than of A. doliolum. The inhibitory effect of copper on urea uptake and urease activity was mitigated by sulphur containing amino acids (cystine and cysteine), however, methionine could not do so, indicating the involvement of sulfhydryl (-SH) groups in the assimilation of urea in cyanobacteria.

Nontarget effects of carbaryl and its hydrolysis product, 1-naphthol, towards Anabaena torulosa

The toxic effects of carbaryl and its hydrolysis product, 1-naphthol, singly and in combination, towards a filamentous diazotrophic cyanobacterium, Anabaena torulosa, were determined. The toxicity criteria employed, viz., packed cell volume, chlorophyll a, phycocyanin, carotenoids, heterocyst differentiation and nitrogen fixation, were greatly affected by the toxicants above 25 micrograms/ml concentrations. However, 1-naphthol was more toxic to the diazotroph than was carbaryl. The toxicity was more pronounced when carbaryl and 1-naphthol were in combinations even at lower concentrations.