- Volume 81, Issue 2, 1974

Summary: An anucleolate mutant (AN) was isolated from the cellular slime mould, Dictyostelium discoideum. The AN developed normally until the beginning of culmination, when development stopped and no differentiation of the spore or stalk cell occurred. The AN had nucleoli at the vegetative stage, but lost them after formation of a cell mass, in contrast to the wild type (WT) which possessed them throughout development. AN cells disaggregated from a slug, reconstructed nucleoli and resumed vegetative growth. Difference in tetrazolium reduction between the prestalk cell and the pre-spore cell, as observed in the WT, was not detected in the AN, although vacuoles specific to the pre-spore cell were formed. When the WT and AN cells were mixed, they aggregated together, but no interaction in cell differentiation was observed. The roles of nucleoli in the development of this organism are discussed.

Summary: Examination of thin sections of sporulating wild-type colonies revealed new structural details of the development of the sporulation-septum walls. Spores with very thick (about 75 nm) three-layered walls were seen in spore preparations.

Of the sporulation defective (whi) mutants examined, whiDI6 was defective in spore-wall thickening while whiF99 was defective in rounding up and produced rod-shaped, thick-walled spores. A third mutant (whi-92) showed occasional abnormality in sporulation-septum spacing and produced immature as well as mature spores. One mutant (whi-53) produced only a few spores, all structurally normal. In two whiE mutants, structural abnormalities in spores were absent or rare.

SUMMARY: In Neurospora crassa the conversion of quinate and shikimate to protocatechuate is catalysed by three inducible enzymes. Previous studies have demonstrated that the qa-1 locus encodes a multimeric regulatory protein which is required for the synthesis of the three catabolic enzymes. The qa-2 locus has been shown to encode catabolic dehydroquinase. This work defines two new classes of mutants. The qa-3 locus is the structural gene for a bifunctional enzyme which catalyses the dehydrogenation of quinate and shikimate. Mutants of the qa-4 class specifically lack 5-dehydroshikimate dehydrase. Alleles of the four different qa mutant classes are tightly clustered and are located to the left of me-7 in L.G. VII.

SUMMARY: The regulation of the synthesis of the first three enzymes of the quinate- shikimate catabolic pathway in Neurospora crassa has been studied. Induction of these enzymes is promoted efficiently by quinate and less so by 5-dehydroquinate and/or 5-dehydroshikimate. Shikimate has little or no inducing ability. The kinetics and steady-state rates of synthesis of the three catabolic enzymes have been examined. It is suggested that quinate-shikimate dehydrogenase, catabolic dehydro- quinase, and 5-dehydroshikimate dehydrase are regulated coordinately.

SUMMARY

The biochemical modifications of two yeast strains, a/α and α/α, have been studied during incubation in a sporulation medium. The increases in dry cell weight, protein, carbohydrate and lipid contents, as well as the variation in respiration rate are quite similar for the two strains. Mating type gene control of sporulation is discussed.

Haemophilus influenzae r f possesses two distinct host specificity systems F1 and F2 each of which is able to restrict and modify Haemophilus phage HP1c1, while strain Rb possesses only one system, B. Among restriction-deficient mutants isolated from strain r f, the r−m+ as well as r−m− phenotypes for these two systems were obtained after either one or two mutational steps. The F1 system was introduced into H. influenzae Rd by genetic transformation to show that the D1 and F1 systems are not allelic.

Strain r e of Haemophilus influenzae carries two genetically distinct host-specificity systems E1 and E2 each of which is able to restrict Haemophilus phage HP1c1 and each of which confers a specific modification upon phage grown in strain r e. These two systems are apparently identical to the host-specificity systems of H. influenzae r fF1 and F2.

SUMMARY

Three classes of cytochrome a deficient mutants of Bacillus subtilis have been isolated. These classes were defined by concentration ratios of cytochromes a, b and c relative to the parent strain, and by responses to non-fermentable substrates.

The cytochrome deficiencies were not due to blocks in haem biosynthesis or to failure of the control mechanisms which alter the respiratory chain during growth of B. subtilis. Mutational loss of cytochrome a did not reduce proportionately the rate of oxygen consumption by late exponential phase cells, although exponential growth rates were generally lower than the parent strain. The cytochrome system of wild-type B. subtilis appears to contain cytochromes a (or a + a 3), b, c, c1 and o.

A previously unreported absorption maximum at 617 nm was discovered, which was elevated in some of the cytochrome a deficient mutants. In these mutants, a new maximum also appeared at 627 nm.

Summary: Nine mutants of Aspergillus nidulans differing in cleistothecia and/or conidia production were investigated. The strains were grown on four media with different levels of glucose (0·8, 3, and 4%) and nitrate (0·6 and 0·15%). The mycelia were analysed on the basis of the dry weight of the total mycelium and the alkali-soluble fraction (containing the α-1,3 glucan) as well as enzyme activities lytic to α-1,3 glucan, laminarin, and starch. Low quantities of α-1,3 glucan present on the third day are correlated with low ±-1,3 glucanase activity and absence of cleistothecia formation on the sixth day. α-1,3 Glucan and cleistothecium formation seemed to be inversely related to conidiation.

SUMMARY: Using crossing and analysis procedures similar to those applied to Streptomyces coelicolor a3(2), several auxotrophic and streptomycin-resistant markers were located on a circular linkage map of the melanin-producing Streptomyces glauces- cens, strain eth22794. The linkage map of S. glaucescens is similar to that of S. coelicolor a3(2), in the sequence of markers and in the presence of two long ‘silent’ regions.

SUMMARY: With a liquid membrane potassium-sensitive electrode it was shown that lethal concentrations of the polyene antibiotics amphotericin B, candicidin and nystatin caused leakage of 90% of non-bound potassium ions from Candida albicans. Accurate and rapid determinations of rates of potassium leakage were made directly in suspensions of Candida. Leakage patterns for the three polyenes were very similar, suggesting a common site of action. Differences were noted in the rates of potassium efflux with organisms from cultures of differing ages.

The polyene antibiotic candicidin is a potent antifungal agent acting upon the cell membrane of Candida albicans. Destruction of selective permeability by polyenes allows cations to leak into the environment and permits the entry of protons to neutralize the charge so created, causing internal acidification. Quantitive studies on proton entry reveal that K+ leakage alone is not sufficient to account for the degree of acidification recorded. Extracts of untreated C. albicans, when acidified to the same extent, precipitated. Electron micrographs of candicidin treated C. albicans cells confirm this precipitation.

SUMMARY: The production of bacitracin by Bacillus licheniformis closely paralleled growth in a synthetic medium without glucose: Glucose inhibited bacitracin production during the first hours of growth, whereas growth was not affected. Bacitracin was produced mainly during the later stages of growth. Formation of bacitracin was apparently not under catabolite repression control by glucose since the inhibitory effect of glucose upon the early bacitracin production was prevented by neutralizing the culture fluid with CaCO3. The inhibitory effect of glucose may be due to the low pH created by its metabolism.

Addition of 0·5 % glucose markedly increased the maximum titre of bacitracin. This stimulation could also be due to the effect of glucose metabolism upon the pH of the medium. The observation that peptide antibiotics are produced mainly after growth is not always true; in appropriate media they might also be produced during the phase of rapid growth.