Effect of UV-C on thylakoid arrangement, pigment content and nitrogenase activity in the cyanobacterium Microchaete sp.

The effect of UV-C radiation on thylakoid arrangement, chlorophyll-a and carotenoid content and nitrogenase activity of the cyanobacterium Microchaete sp. was studied. Chlorophyll-a and carotenoid content increased gradually up to 48 h of UV-C exposure but declined with longer exposures. Nitrogenase activity decreased moderately with 6 to 12 h exposure and decreased substantially afterwards. When cells exposed to UV-C for 12 to 24 h, grown under fluorescent light for 144 h, nitrogenase activity increased to levels greater than in the control cells. The exposure of UV-C treated cells to fluorescent light, however, did not result in recovery of pigment content. In Microchaete sp. cells treated with UV-C for 144 h, thylakoid membranes became dense, were aggregated into bundles, and were surrounded by spaces devoid of cytoplasm.

Scavenging of nickel and chromium toxicity in Aulosira fertilissima by immobilization: effect on nitrogen assimilating enzymes

The ubiquity of heavy metals in the biosphere results in the introduction of high amounts of toxic metals into the food chain from various sources. In the present study, one of the strongest nitrogen fixing cyanobacterium of the rice fields, Aulosira fertilissima, was subjected to nickel and chromium stress and the ameliorating effect of immobilization was investigated. Cell immobilization could protect the organism's growth against the toxicity of both heavy metals at LC50 as compared to lethal concentrations. The nitrate reductase activity in free cells treated with the metals was substantially inhibited but immobilized cells treated with 0.1 ppm nickel was not affected by the metal treatment. Cell immobilization also resulted in a significant protection against sub-lethal concentration of chromium but to a lesser degree than it did with sub- lethal levels of nickel. Control immobilized cells also had higher Nitrogenase activity than control free cells. Nickel and chromium addition markedly decreased the enzyme activity in free cells but immobilized cells exposed to sublethal concentrations of both metals could overcome this decrease. Glutamine synthetase showed similar response under immobilized conditions compared to free cells with both metals. The addition of algal filtrate in 3:1 ratio further increased the nitrogenase activity compared with immobilized cells treated with sublethal doses of both metals. Immobilization facilitated higher uptake of nickel as compared to chromium. The observations of the present study clearly demonstrate the protective effect of immobilization on Aulosira fertilissima against Nickel and chromium toxicity. Rice field ecosystem thus possess a bidirectional natural metal ameliorating system where Aulosira mats act as a naturally immobilized system and the decay of Aulosira along with other cyanobacteria act as natural chelators protecting the rice plants from deleterious effects of the heavy metals. Most importantly is...

Biologically active peptides in cyanobacteria

Las cianobacterias se encuentran en el medio natural tanto en aguas dulces como saladas. Ellas pueden desarrollarse en grandes masas formando "blooms" (florecimientos) en aguas dulces y saladas en diferentes partes del mundo, incluyendo América del Sur. Tales florecimientos, así como crecimientos axénicos de cianobacterias, pueden ser una rica fuente de péptidos lineales o cíclicos únicos, muchos de los cuales presentan actividad biológica. En el pasado la mayor atención ha sido puesta en las toxinas microcistina y nodulatoria. Estos péptidos ciclicos son hepatotoxinas que inhíben la proteína fosfatasa 1 y 2A, después de ingresar específicamente al hepatocito mediante la captación de las sales biliares. Sin embargo, en cianobacterias se están encontrando péptidos con otras actividades biológicas. No obstante, auque no se consideren tóxicos, estos péptidos tienen actividades biológicas tales como: una fuerte y específica inhibición de las proteasas (tripsina, quimo-tripsina, elastasa, trombina, plasmina y la enzima procesadora angiotensina), anticianobacterias, antialgas, antihongos, inmunosupresores y promotores de diferenciación celular. Ejemplos de péptidos cianobacteriales inhibidores de proteasas son las cianopeptolina. Las interacciones de microcistina/proteína fosfatasa y de cianopeptolina/proteasa, han sido bien estudiadas por difracción de rayos x en cocristales y la determinación de microcistina y de otros péptidos puede ser realizada por métodos químicos y biológicos. Ambas, microcistina y cianopeptolina han sido recientemente determinadas en blooms producidos en cuerpos de agua en Chile, utilizando cromatografía líquida de alta resolución (HPLC), espectrometría de masas (MALDI-TOF) (PSD), además de bioensayos de inhibición enzimática

Glutamine synthetase from N2-fixing cyanobacterium Nostoc muscorum--purification, biochemical and immunological characteristics.

A modified procedure for purification of glutamine synthetase [L-glutamate: ammonia ligase (ADP-forming)] from N2-fixing cyanobacterium N. muscorum, to homogeneity is described using DEAE-Sephadex and Blue-Sepharose affinity chromatography. Specific activities of the purified enzyme in biosynthetic and transferase assays were 8.5 and 28 mumole product formed min-1 mg-1 protein. Apparent molecular mass of native GS enzyme was about 610 kDa as estimated by gel filtration. On SDS-PAGE the enzyme protein migrated as single band with molecular weight of 51 kDa. Apparent Michaelis Menten constant (Km) for glutamate, glutamine, ATP and ammonium were 2.8, 4.0, 0.35 and 0.82 mM respectively. Ammonium and structural analogues of glutamine and ammonium viz, methionine sulfone (MSO), methionine-DL-sulfoximine (MSX), ethylenediamine (EDA) and glyphosine significantly inactivated the enzyme activity while azaserine showed partial inhibition. Polyclonal antibodies raised against purified GS protein of N. muscorum showed high specificity to both crude and pure GS preparations in different immunological assays like double diffusion, rocket immunoelectrophoresis, ELISA and western blotting. With serological procedure a microquantity of GS-antigen upto 2 ng in vivo and immunological relationship of the protein with different strains have been documented.

Effect of lead on nitrogenase and enzymes of nitrogen assimilation in a cyanobacterium Nostoc muscorum.

Lead decreased the growth rates, total cell mass, heterocyst frequency, total cell protein, nitrogenase activity, glutamine synthetase (GS) and glutamate synthase (GOGAT) activities in N:muscorum. However, lead at 0.01 and 10 micrograms ml-1 conc. enhanced nitrogenase as well as GS activity of the cells. On transfer to excess lead (100 micrograms ml-1), nitrogenase and GS activities ceased almost after 24 hr in the cyanobacterium. It is deduced that lead has a two step effect on stimulation and inhibition of metabolic activity at 0.01 and 10 micrograms ml-1 concentration and 0.1 and 100 micrograms ml-1 concentration respectively indicating a close interaction between nitrogen fixation and GS activity. However, GOGAT activity is an exception to this two step stimulation and inhibition process.

Phosphatase activities and phosphorous fractions in two periphytic cyanobacteria in response to some pesticides

The addition of dursban, dimethoate, karathane and trifluralin at various doses to the nutrient medium of Anabaena oryzae and Nostoc muscorum resulted in significant increase in the total posphorous contents of both organisms as well as in the total soluble, total insoluble, inorganic and organic posphorous fractions. Irrespective of some minor fluctuations, the accumulation of DNA-P and RNA-P was progressively increased. However, the magnitude of this effect differed among the two cyanobacteria. The activities of acid and alkaline phosphatases were accelerated following all pesticide applications, depending on the organism, the pesticide, its dosage and on prevailing conditions. Differences between Nostoc and Anabaena in phosphatase activities could be due to differences in the potential of the organisms to degrade the pesticide, or to differences in competitive and noncompetitive stimulatory and/or inhibitory action of the different pesticides upon acid and alkaline phosphatases