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.

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

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.

Extracellular phycoerythrin-like protein released by freshwater cyanobacteria Oscillatoria and Scytonema sp.

During growth of the freshwater cyanobacteria, Oscillatoria sp. BTCC/A0004, and Scytonema sp. TISTR 8208, a pink pigment is released into the growth medium. The pigment from each source had a molecular weight of approximately 250 kDa and had adsorption maxima at 560 and 620 nm. These results suggest that pink pigment is a phycoerythrin-like protein. It inhibited the growth of green algae, Chlorella fusca and Chlamydomonas reinhardtii, but not other cyanobacteria or true bacteria. The concentration at which growth inhibition 50% occurred was 0.5, 6 and more than 10 mg ml(-1), respectively.

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.

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).