Aparat Mahakhant

Bioactivities of nostocine a produced by a freshwater cyanobacterium Nostoc spongiaeforme TISTR 8169.

A freshwater cyanobacterium, Nostoc spongiaeforme TISTR 8169, synthesizes and releases a violet pigment, nostocine A, into medium. We examined the bioactivity of nostocine A to several model organisms breeding with N. spongiaeforme in the natural environment. To microalgae, nostocine A exhibited growth inhibitory activity comparable to paraquat, and the activity tended to be stronger to green algae than to cyanobacteria. Nostocine A also exhibited strong inhibitory activity to the root elongation of barnyard grass, strong antifeedant activity to cotton ballworm, and acute toxicity to mice resulting in its classification as a dangerous poison. The results suggest that nostocine A may act as a toxin or an allelochemical to breeding organisms in nature. In a laboratory culture of N. spongiaeforme, the production of nostocine A was enhanced at higher temperature, 30 degrees C, and more intense light, 30 W/m2, than the basal conditions, 25 degrees C and 10 W/m2. Cultivation of cells with H2O2 at 1 or 2 mM also enhanced the production of nostocine A, indicating that nostocine A may be synthesized and released when the cells are exposed to oxidative stress, possibly occurring at higher temperature and more intense light. LC-MS and electron spin resonance analyses revealed that nostocine A, reduced previously by NaBH4, immediately recovered to its original form upon exposure to air and the generation of superoxide radical anions occurred at this re-oxidation step. These results suggest that the adverse effects of nostocine A on various organisms may be related to the function of nostocine A in generating toxic reactive oxygen species, which occurs in the cells of target organisms.

Detection of microcystins from cyanobacterial water blooms in Thailand fresh water

Microcystin content and composition in water blooms collected from two reservoirs and a pond in Thailand were investigated. The dominant species in the water blooms were Microcystis aeruginosa Pleurocapsalean filamentous cyanobacterium. The water blooms contained 0.7–0.8 mg microcystin/g dried sample. This is the first identification of microcystin from Pleurocapsalean filamentous cyanobacterium. The major microcystins in the water blooms were microcystin ‐RR, ‐LR and their (Z) forms as geometrical isomers. Microcystin ‐YR, ‐LA, ‐ThtyrR and ‐AR were also detected as minor variants. A novel variant, L‐2‐amino‐N‐butyric acid‐containing microcystin (microcystin ‐lBu), was identified from water blooms in a pond in Bangkok.

Improved Alkane Production in Nitrogen-Fixing and Halotolerant Cyanobacteria via Abiotic Stresses and Genetic Manipulation of Alkane Synthetic Genes

Cyanobacteria possess the unique capacity to produce alkane. In this study, effects of nitrogen deficiency and salt stress on biosynthesis of alkanes were investigated in three kinds of cyanobacteria. Intracellular alkane accumulation was increased in nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, but decreased in non-diazotrophic cyanobacterium Synechococcus elongatus PCC7942 and constant in a halotolerant cyanobacterium Aphanothece halophytica under nitrogen-deficient condition. We also found that salt stress increased alkane accumulation in Anabaena sp. PCC7120 and A. halophytica. The expression levels of two alkane synthetic genes were not upregulated significantly under nitrogen deficiency or salt stress in Anabaena sp. PCC7120. The transformant Anabaena sp. PCC7120 cells with additional alkane synthetic gene set from A. halophytica increased intracellular alkane accumulation level compared to control cells. These results provide a prospect to improve bioproduction of alkanes in nitrogen-fixing halotolerant cyanobacteria via abiotic stresses and genetic engineering.

Phycoerythrin-containing Microcystis isolated from P.R. China and Thailand

Four strains of the unicellular, colonial cyanobacteria, Microcystis were isolated from P.R. China and Thailand, and showed greyish‐brown to dark brown color of cell mass. Their cells were almost spherical, 3.8–5.5 μm in diameter and had gas vesicles. Their colony forms have some differences among the strains but still have common characteristics including being irregular, reticulate, elongated and lobated. These characteristics are remarkably similar to Microcystis aeruginosa (Kutz.) Kutz. In addition, three of the strains also have the characteristics of Microcystis ichthyoblabe Kutz at times, and another sometimes shows characteristics similar to Microcystis novacekii (Kom.) Comp. The absorption spectra of both intact cells and extracted phy‐cobiliproteins showed an absorption peak at 560–570 nm in wavelength, which is the absorption range of phycoerythrin. Since no species of Microcystis has ever been reported to have phycoerythrin, the existence of phycoerythrin separates these four strains from the known species of Microcystis, and might enable them to be classified as a new species. Phycoerythrin might give these organisms the advantage to live underwater where the light is predominantly green in color.

Control of the plant pathogenic fungus Macrophomina phaseolina in mung bean by a microalgal extract

An anti‐fungal antibiotic was characterized from an extract of Calothrix sp. TISTR 8906 with respect to an inhibition effect on plant pathogenic fungi. Optimal medium for anti‐fungal compound production was modified from nitrogen‐free BGA medium by the addition of NaN03 at the concentration of 1.5gL‐1, increasing K2HP04 concentration to 1.5 g L‐1 and decreasing NaCl concentration to 0.03 g L‐1 with an initial pH of 7.0. Algal growth, anti‐fungal activity and anti‐fungal compound production could be increased 2.6‐fold, four‐fold and 10‐fold, respectively. Crude algal extract formulated with surfactant applied to Macrophomina phaseolina at a concentration of 250 μg seed‐1 showed the same efficiency at inhibition as the commercial fungicide, mancozeb, at the recommended dose of 200 μg seed‐1, both in laboratory and pot experiments.

Caleosin from Chlorella vulgaris TISTR 8580 is salt-induced and heme-containing protein

Graphical Abstract Changes of accumulation levels for lipid droplet (A) and caleosin mRNA from Chlorella vulgaris TISTR 8580 cells Physiological and functional properties of lipid droplet-associated proteins in algae remain scarce. We report here the caleosin gene from Chlorella vulgaris encodes a protein of 279 amino acid residues. Amino acid sequence alignment showed high similarity to the putative caleosins from fungi, but less to plant caleosins. When the C. vulgaris TISTR 8580 cells were treated with salt stress (0.3 M NaCl), the level of triacylglycerol increased significantly. The mRNA contents for caleosin in Chlorella cells significantly increased under salt stress condition. Caleosin gene was expressed in E. coli. Crude extract of E. coli cells exhibited the cumene hydroperoxide-dependent oxidation of aniline. Absorption spectroscopy showed a peak around 415 nm which was decreased upon addition of cumene hydroperoxide. Native polyacrylamide gel electrophoresis suggests caleosin existed as the oligomer. These data indicate that a fresh water C. vulgaris TISTR 8580 contains a salt-induced heme-protein caleosin.