- Volume 134, Issue 9, 1988

Carotenoid-overproducing mutants of Azospirillum brasilense Sp7, which contained about 100 times more carotenoids than the wild-type, were obtained after nitrosoguanidine mutagenesis. Growth studies with one of these mutants in oxygen-controlled batch and continuous cultures revealed a slightly improved oxygen tolerance of nitrogen fixation in the mutant as compared to the wild-type. The production of carotenoids was greatly enhanced by increasing the oxygen concentration under nitrogen-deficient conditions. Although nitrogen fixation was severely inhibited by increased oxygen concentrations, in both the mutant and the wild-type, the mutant showed significantly greater efficiency of nitrogen fixation at 12μm dissolved oxygen, and it fixed five times more total nitrogen than the wild-type under these conditions. In conclusion, high levels of carotenoids slightly enhanced the oxygen tolerance of Azospirillum brasilense under conditions of oxygen stress, but did not extend the optimum pO2 for nitrogen fixation to higher oxygen concentrations.

To establish a balance between the ATP produced in catabolism and the ATP consumed in net biosynthesis of cellular components the energy metabolism of Saccharomyces cerevisiae utilizing glucose in the absence of a nitrogen source (resting cells) was studied. The following results were obtained. (i) Cell number and biomass increased 2- and 2·5-fold, respectively, during the first 8 h of ammonium starvation. After this period, both values remained constant. (ii) The rate of sugar consumption and ATP production decreased with the duration of starvation to about 20% of the original in 24 h. (iii) About 60% of the sugar consumed was fermented to ethanol and about 10% assimilated as cellular material. Of the assimilated sugar, as much as 80% was accumulated as carbohydrate. (iv) Only 15% of the total ATP produced in catabolism seems to be consumed in net biosynthesis and maintenance of intracellular pH. The fate of the remaining 85% is unknown.

At least 14 phosphopolypeptides in which the phosphate groups were present as mono-esters were detected by pulse labelling of Bacillus thuringiensis subsp. kurstaki HD-1-Dipel with [32P]orthophosphate at different stages of growth and differentiation. Marked changes in the profile of phosphopolypeptides were observed primarily during the late exponential phase of growth. Several phosphopolypeptides co-purified with the endotoxin crystal of this subspecies and the phosphoamino acid residue of the most abundant (M r 25000) phosphopolypeptide was identified as phosphothreonine. Comparison of the phosphopolypeptides in endotoxin crystals from several subspecies suggested that M r 25000 species might be a common component.

Aerobic cultures of Staphylococcus simulans biovar staphylolyticus characteristically achieved about 17 times higher bacterial densities and produced about 7 times higher concentrations of exoprotein than did anaerobic cultures. However, total exoprotein secreted per unit of bacterial dry weight typically was 2·3 times greater for anaerobic cultures. As determined by SDS-PAGE, anaerobic cultures also produced a wider variety of exoproteins than did aerobic cultures. Three exoenzymes, a staphylolytic endopeptidase, a micrococcolytic hexosaminidase and a thiol protease, were completely repressed during anaerobic growth, which is further evidence for coordination of their production.

We report initial attempts to define the role of Ca2+ in the polarized extension of Neurospora crassa. Growth of the organism was diminished in media containing less than 1 mM-Ca2+; extension was more severely impaired than biomass synthesis, resulting in the formation of stubby, bulbous hyphae, even of spherical cells. Reduced extension and abnormal morphology were correlated with the loss of surface-bound Ca2+, probably associated with the cell wall. Intracellular Ca2+ may be represented by material that fluoresces brightly in the presence of chlortetracycline. Punctate fluorescent bodies and diffuse fluorescence were both arrayed in a longitudinal gradient, maximum apically. Addition of the calcium ionophore A23187 induced dissipation of the fluorescence; concurrently, the hyphae lost as much as one half of their Ca2+ content. Extension continued almost unabated, but multiple branches quickly emerged from the apex. The observations suggest that a cytoplasmic Ca2+ gradient is not required for polarized extension, but may play a role in ensuring the dominance of the apex.