- Volume 110, Issue 2, 1979

SUMMARY: Nitrogen starvation and heterocyst development were induced in the cyanobacterium Anabaena 7120 by growth in nitrogen-free medium or by treatment with the amino acid analogue methionine sulphoximine. During the first 6 h of nitrogen deprivation, amino acid levels and rates of protein synthesis, as measured by the incorporation of [3H]leucine, decreased to 50 to 70% of those in ammonia-grown organisms; after this time there was no difference between the rates of protein synthesis in ammonia-grown and nitrogen-starved cultures. The period 4 to 12 h after the onset of starvation was marked by the release of [3H]leucine from previously labelled proteins at a rate 6 to 7·5 times that of ammonia-grown organisms. These results are consistent with the idea that nitrogen starvation in cyanobacteria causes a reduction in protein synthesis and leads to the rapid degradation of storage proteins. In rapidly growing Anabaena 7120, the doubling time for total cell protein was estimated to be 14·9 ± 1·0 h and the half-life was 139 ± 88 h.

SUMMARY: Approximately 500 vitamin B6 auxotrophs were isolated from 18 independent cultures of Escherichia coli strain CR63. None grew in minimal medium supplemented with 2′-hydroxy-pyridoxine. Eighteen auxotrophs which had arisen independently were further characterized. All of them were defective in vitamin B6 synthesis rather than in an aminotransferase involved in vitamin B6 utilization. Two different phenotypes were recognized: ‘Oxidase’ mutants which grew only when supplied with pyridoxal or pyridoxal 5′-phosphate and ‘Pre Pn’ mutants which would also grow with pyridoxine or pyridoxine phosphate. ‘Oxidase’ mutants were confined to a single linkage group, but data from interrupted mating experiments established that ‘Pre Pn’ mutants fall into two linkage groups which are possibly identical to pdxA and pdxB. All mutations in the pdxA region were allelic rather than located in two closely linked genes.

SUMMARY: In decadent sporulation mutants, sporulating populations are heterogeneous: the cells reach successive chemical and physical resistances with progressively decreasing frequencies. Each decadent mutant can be characterized by the shape and slope of the curve describing the frequency of cells resistant to various agents (‘the resistance spectrum’). In some mutants the resistance spectrum decreases progressively from xylene resistance to heat resistance; in other mutants it decreases rapidly between octanol resistance and chloroform resistance. Electron microscopy showed that in two mutants the majority of the cells are blocked at stages III and IV; the number of cells that develop further to reach successive morphological stages falls off progressively. In two other mutants most cells reach stage V. Cortex-less spores are also frequent. One of the decadent mutations, SpoL1, was localized between aroD and acf. The phenotype of decadent mutants is discussed in terms of sequential gene activation.

SUMMARY: A strain of Sporotrichum thermophile (var. 2), grown in submerged culture at 44°C, decayed crystalline cellulose by the secretion of cellulolytic enzymes into the culture medium. Dialysed culture filtrates, after growth on cellobiose, were also effective in degrading crystalline cellulose (Avicel). Cellulase, measured viscometrically with carboxymethylcellulose as substrate and therefore referred to as CM-cellulase, was induced by cellulose, glucomannan, cellobiose and, to a limited extent, by laminaribiose and cellobionic acid. Low CM-cellulase activities were also detectable when the organism was grown on other carbon sources. In culture media supplemented with readily metabolized non-inducing substrates, such as glucose, CM-cellulase activity did not increase after their exhaustion indicating that no derepression of constitutive CM-cellulase occurred. CM-cellulase synthesis induced during growth on cellobiose was strongly inhibited, although not completely suppressed, by glucose and other carbon sources. In cultures grown on glucose and cellobiose, glucose was utilized first and CM-cellulase synthesis was repressed; cellobiose utilization occurred only after glucose exhaustion and triggered CM-cellulase formation. When glucose was added to a culture growing on cellobiose, further utilization of the latter was prevented and CM-cellulase synthesis was inhibited. The use of glucose analogues gave some indications that cellobiose did not compete with glucose for the same transport carrier and that glucose catabolism was a prerequisite for the inhibition of CM-cellulase synthesis.