Germaine Cohen-Bazire

The path of carotenoid synthesis in a photosynthetic bacterium

Abstract Exponentially growing cells of the photosynthetic bacterium Rhodospirillum rubrum contain a mixture of carotenoids: lycopene, P481, spirilloxanthin, and their monohydroxy derivatives. When such cells are resuspended in buffer and incubated anaerobically in the light, the total amount of carotenoid pigment in the cells remains constant, but there is a net synthesis of spirilloxanthin at the expense of the other carotenoids originally present. This synthesis proceeds from lycopene through P481. Added to a photosynthetically growing culture of R. rubrum at a final concentration of 7 · 10 −5 M , diphenylamine causes a complete arrest of normal carotenoid synthesis, accompanied by a rapid accumulation of carotenoids more saturated than lycopene. Phytoene, phytofluene, hydroxyphytofluene, ζ-carotene, hydroxy-ζ-carotene, neurosporene and hydroxyneurosporene are the principal accumulating compounds. If the diphenylamine is removed and the cells are resuspended in buffer and incubated anaerobically in the light, an endogenous synthesis of normal carotenoids takes place at the expense of all the accumulated precursors with the probable exception of phytoene. The kinetic analysis of this endogenous synthesis reveals the sequential relationships between the participating carotenoids.

Nitrogen fixation by unicellular blue-green algae

SummaryThe ability of some unicellular blue-green algae to grow at the expense of N2 under aerobic conditions has been confirmed and the distribution of this property in the Chroococcaceae has been investigated. It appears to be confined to strains with spherical cells enclosed by the multilaminate sheaths characteristic of the genus Gloeocapsa. Only two unicellular blue-green algae of this type are now available in pure culture; and their properties are so similar that they may well be independent isolates of the same species.No differences in structure between cells grown with nitrate and N2 could be detected, either by light or by electron microscopy; under both conditions of growth, the population consists entirely of vegetative cells. These two Gloeocapsa strains can therefore maintain a functional nitrogenase system in vegetative cells that are freely exposed to air.

Characterization of phycoerythrin from a Cryptomonas sp.

SummaryTwo closely similar phycoerythrins were purified from Cryptomonas sp. The two proteins were indistinguishable with respect to native molecular weight, subunit structure, photolability and immunological specificity, and differed only in their isoelectric points (pH 5.74 and 6.35), as determined by isoelectric focussing in polyacrylamide gels. Each protein consisted of two unequal subunits, α (mol. wt. 11,800) and β (mol. wt. 19,000), and each subunit contained covalently bound chromophore. In contrast to the blue-green and red algal phycoerythrins studied thus far, the Cryptomonas sp. phycoerythrins are extremely photolabile; exposure of the purified proteins to relatively short periods of intense illumination with visible light produces a marked decrease in fluorescence and in absorbance at 567 mμ.

Mutations of Anacystis nidulans that affect cell division

SummaryFollowing nitrosoguanidine treatment of the blue-green alga Anacystis nidulans strain 6311, mutants which grow predominantly as short or long filaments are commonly produced. Cytological study shows that the filaments are multinucleate, coenocytic structures. Such mutations are therefore best interpreted as ones that impair cell division in a normally unicellular organism.

The Internal Membranes of Caulobacter Crescentus

SUMMARY: The intracytoplasmic membranous structures previously observed in various caulobacter species by electron microscopy of thin sections were studied further by electron microscopy of whole organisms of Caulobacter crescentus negatively stained with phosphotungstate. The large, complex mesosomes are intrusions of the cell membrane. They appeared, from their central location in dividing cells, to play a role in division. Smaller and less involuted intrusions of the membrane became abundant in oxygen-limited cells, which also had an abnormally high content of haem pigments. These smaller intrusions may therefore be a structural reflexion of an increased content in the membrane of components of the respiratory electron transport system. The membranous organelle which occurred at the site of stalk formation and appeared to be connected with the membranous core of the stalk was not penetrated by phosphotungstate, and therefore had an organization different from that of the mesosome.