MORPHOLOGICAL AND PHYLOGENETIC STUDIES ON UNICELLULAR DIAZOTROPHIC CYANOBACTERIA (CYANOPHYTES) ISOLATED FROM THE COASTAL WATERS AROUND SINGAPORE(1).

Six unicellular diazotrophic cyanobacteria were isolated from the coast around Singapore. The isolates grew under both light:dark (L:D) cycles and continuous illumination (CL) in media without combined nitrogen and exhibited an ability to fix nitrogen (as measured by acetylene reduction) under aerobic conditions. The cells of all isolates were surrounded by a thick fibrous outer wall layer, and they divided by transverse binary fission. The arrangement of photosynthetic thylakoids was of the dispersed type. Three isolates were identified as form-genus Gloeothece as cells were divided in a single plane, and the other three isolates were identified as form-genus Gloeocapsa as cells were divided in multiple planes. Phylogenetic analyses based on the DNA sequences of the genes encoding 16S rRNA and dinitrogenase reductase (nifH) revealed the following: (i) Our six isolates formed a monophyletic cluster. (ii) The monophyletic cluster was subdivided into two phylogenetic groups, which taxonomically corresponded with the form-genera Gloeothece and Gloeocapsa. However, (iii) a diazotrophic strain of form-genus Gloeothece, Gloeothece membranacea (Rabenh.) Bornet PCC6501, was not closely related to our isolates, and (iv) some, but not all, diazotrophic unicellular strains of form-genus Cyanothece were observed to be in a close relationship with our isolates.

Photoproduction of hydrogen by the marine heterocystous cyanobacterium Anabaena species TU37-1 under a nitrogen atmosphere.

Hydrogen production rates by Anabaena sp. strain TU37-1 obtained after an initial 1-day incubation period were approximately 70 to 80 and 3 to 9 micro mol (mg chl)(-1) h(-1) under argon and nitrogen atmospheres, respectively. Hydrogen production under argon was not enhanced by addition of carbon dioxide, but was enhanced to some extent under nitrogen by increasing the initial carbon dioxide concentration. Rates of hydrogen and oxygen production during the initial 7-hour period were 15 and 220 micro mol (mg chl)(-1) h(-1), respectively, in vessels with 18.5% initial carbon dioxide. Hydrogen production under nitrogen was enhanced by addition of carbon monoxide (1%). The rate obtained from the initial 1-day incubation period was about 40 micro mol (mg chl)(-1) h(-1), which corresponded to about 60% of that under argon. On the basis of these observations, a possible strategy for hydrogen production by nitrogen-fixing cyanobacteria under nitrogen in the presence of carbon monoxide is indicated.