Production of ketocarotenoids by microalgae.

Among the highly valued ketocarotenoids employed for food coloration, astaxanthin is probably the most important. This carotenoid may be produced biotechnologically by a number of microorganisms, and the most promising seems to be the freshwater flagellate Haematococcus pluvialis (Chlorophyceae), which accumulate astaxanthin in their aplanospores. Many physiological aspects of the transition of the flagellate into aplanospores have been described. Mixotrophic cultivation and suitable irradiance may result in fairly good yields (up to 40 mg/l; 43 mg/g cell dry weight) within a reasonable time, under laboratory conditions. In order to compete with synthetic astaxanthin, suitable scaling-up is required. However, large-scale production in open ponds has proved unsatisfactory because of severe contamination problems. A selective medium might overcome this difficulty. Further research for the development of suitable strains is thus warranted.

Ethanol fermentation by nystatin-resistant strains of Saccharomyces cerevisiae.

Nystatin-resistant mutants of haploid and polyploid strains of Saccharomyces cerevisiae were isolated by plating on gradient plates with increasing nystatin concentrations (60-3000 U/ml). Some of the mutants were defective in ergosterol biosynthesis, and produced zymosterol and cholestatetraenol-like sterols. Those mutants which do not form ergosterol produce less ethanol than the parent strains. They also had lower viability during fermentation of glucose solutions (8-13% vs. 33-47%). This became more pronounced in fermentations of higher concentrations of glucose. A nystatin-resistant but ergosterol-forming mutant had a similar fermentation capacity to the parent strain.

Effect of glucose on carbon dioxide assimilation and substrate oxidation by Ferrobacillus ferrooxidans.

Ferrobacillus ferrooxidans, grown on either elemental sulfur or ferrous sulfate, was able to use either substrate as an energy source for the assimilation of CO(2). In both cases, 0.01 mumole of carbon was incorporated per mumole of oxygen utilized. Glucose inhibited substrate oxidation and CO(2) fixation. Sulfur and iron oxidation were inhibited 5 to 15% and 40 to 50%, respectively, in the presence of 10% glucose. Under the same conditions, CO(2) assimilation was inhibited 50% with elemental sulfur as the energy source, and was almost totally inhibited when ferrous iron was used.

Sulfur oxidation by the iron bacterium Ferrobacillus ferrooxidans.

Margalith, P. (Syracuse University, Syracuse, N.Y.), Marvin Silver, and D. G. Lundgren. Sulfur oxidation by the iron bacterium Ferrobacillus ferrooxidans. J. Bacteriol. 92:1706-1709. 1966.-Sulfur and iron oxidation has been studied manometrically by use of Ferrobacillus ferrooxidans grown on either elemental sulfur or ferrous iron as the primary energy source. The iron-oxidizing enzyme was shown to be constitutive, since iron was oxidized as rapidly by sulfur-grown cells as by iron-grown cells. Sulfur-grown cells had a better capacity for oxidizing sulfur than did iron-grown cells; however, no lag in oxidation was seen in either case. The sulfur-oxidizing system was not inducible, and it is suggested that the different oxidative capacities are due to the heterogeneous mixture of cell types in the culture population.