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We describe within this paper the development of an affinity sensor for the detection of the cyanobacterial toxin microcystin-LR. The first stage of the work included acquiring and testing of the antibodies to this target. Following the investigation, a heterogeneous direct competitive enzyme-linked immunosorbent assay (ELISA) format for microcystin-LR detection was developed, achieving a detection limit, LLD80 = 0.022 μg L-1. The system was then transferred to an affinity membrane sorbent-based ELISA. This was an amenable format for immunoassay incorporation into a disposable amperometric immunosensor device. This membrane-based ELISA achieved a detection limit, LLD80 = 0.06 μg L-1. A three-electrode immunosensor system was fabricated using thick-film screen-printing technology. Amperometric horseradish peroxidase transduction of hydrogen peroxide catalysis, at low reducing potentials, versus Ag/AgCl reference and carbon counter electrodes, was facilitated by hydroquinone-mediated electron transfer. A detection limit of 0.5 μg L-1 for microcystin-LR was achieved. Similar levels of detection could be obtained using direct electrochemical sensing of the dye produced using the membrane-based ELISA. These techniques proved to be simple, cost-effective, and suitable for the detection of microcystin-LR in buffer and spiked tap and river water samples. [ABSTRACT FROM AUTHOR]

The cyanobacterium Synechococcus sp. PCC 7002 carries two genes, petJ1 and petJ2, for proteins related to soluble, cytochrome c6 electron transfer proteins. PetJ1 was purified from the cyanobacterium, and both cytochromes were expressed with heme incorporation in Escherichia coli. The expressed PetJ1 displayed spectral and biochemical properties virtually identical to those of PetJ1 from Synechococcus. PetJ1 is a typical cytochrome c6 but contains an unusual KDGSKSL insertion. PetJ2 isolated from E. coli exhibited absorbance spectra characteristic of cytochromes, although the α, β, and γ bands were red-shifted relative to those of PetJ1. Moreover, the surface electrostatic properties and redox midpoint potential of PetJ2 (pI 9.7; Em,7 148 ± 1.7 mV) differed substantially from those of PetJ1 (pI 3.8; Em,7 = 319 ± 1.6 mV). These data indicate that the PetJ2 cytochrome could not effectively replace PetJ1 as an electron acceptor for the cytochrome bfcomplex in photosynthesis. Phylogenetic comparisons against plant, algal, bacterial, and cyanobacterial genomes revealed two novel and widely distributed clusters of previously uncharacterized, cyanobacterial c6-like cytochromes. PetJ2 belongs to a group that is distinct from both c6 cytochromes and the enigmatic chloroplast c6A cytochromes. We tentatively designate the PetJ2 group as c6C cytochromes and the other new group as c6B cytochromes. Possible functions of these cytochromes are discussed. [ABSTRACT FROM AUTHOR]

The mechanisms of gold bioaccumulation by cyanobacteria (Plectonema boryanum UTEX 485) from gold(III)-chloride solutions have been studied at three gold concentrations (0.8, 1.7, and 7.8 mM) at 25 °C, using both fixed-time laboratory and real-time synchrotron radiation absorption spectroscopy (XAS) experiments. Interaction of cyanobacteria with aqueous gold(III)-chloride initially promoted the precipitation of nanoparticles of amorphous gold(I)-sulfide at the cell walls, and finally deposited metallic gold in the form of octahedral (111) platelets (∼10 nm to 6 μm) near cell surfaces and in solutions. The XAS results confirm that the reduction mechanism of gold(III)-chloride to metallic gold by cyanobacteria involves the formation of an intermediate Au(I) species, gold(I)-sulfide. [ABSTRACT FROM AUTHOR]

Investigates the relationship between photoinactivation of photosystem II and D1 protein turnover under various conditions in the psbO-less and psbH-less mutants as compared to the wild type in order to gain an insight into the relationship between degradation and resynthesis of D1 protein. Materials and methods; Results; Discussion.