- Volume 64, Issue 2, 1970

SUMMARY: DNA breakdown was detected 3 to 4 min. after addition of colicin E2 to sensitive cells; inhibition of cell division followed 5 to 10 min. later, but inhibition of DNA synthesis was observed only after several more minutes. Adsorption of E2, which takes place even at 4°, led to the formation of a specific surface complex (I). Complex I did not promote DNA breakdown. We suggest that the transition from this complex to a surface complex (II) which promoted DNA breakdown depended upon several factors which include temperature, concentration of E2, specific membrane proteins and, under certain conditions, high concentrations of extracellular KH2PO4. The formation of complex II did not depend on concomitant DNA or protein synthesis. The continued promotion of DNA breakdown by complex II and its associated nuclease was blocked by inhibition of energy metabolism. In addition, the removal of E2 from the cell surface by trypsin treatment during the early stages of the process greatly decreased the rate of DNA breakdown. E2-induced DNA breakdown, which appears to commence from a limited number of chromosomal sites, proceeded normally in UVr−-, RecB−-, RecC−-, Hsr−-, Hss−-, PolA−- and in several tsDNA replication mutants.

SUMMARY: The free amino acid pool contents of Gram-negative bacteria (Aerobacter aerogenes, Erwinia carotovora, Pseudomonas fluorescens) were studied as functions of the growth environment and were compared with those from correspondingly grown cultures of Gram-positive bacteria (Bacillus subtilis var. niger, B. megaterium, B. polymyxa) and the yeast Saccharomyces cerevisiae.

Although the pools of the Gram-positive bacteria and the yeast contained five to 20 times the concentration of free amino acids present in the pools of Gram-negative bacteria, all pools were similar in containing only a limited range of detectable amino acids. Glutamate invariably predominated and generally accounted for over 50% of the total amino acid content of the pool. The contents and composition of pools from micro-organisms maintained in steady states in chemostat cultures did not vary with time, but changed significantly with changes in either growth rate or the nature of the growth limitation. However, these pool variations were small compared with those resulting from addition of 2% (w/v) NaCl to a culture of growing bacteria. With cultures of Gram-negative bacteria, sudden changes in medium salinity effected marked and rapid changes in free glutamate content; with Gram-positive bacteria, similar changes occurred, but extremely slowly. Addition of 4% (w/v) NaCl to growing yeast cultures brought about no observed changes in pool size or composition. These results are discussed with reference to the involvement of free amino acids in synthesis and functioning of microorganisms.

SUMMARY: When a culture of Bacillus licheniformis was shifted from aerobic to anaerobic conditions, lysis occurred unless a fermentable carbon source or a system for nitrate respiration was present. Nitrate reductase was primarily induced by partial or complete anaerobiosis and partially repressed by glucose. The enzyme was repressed and inactivated by high oxygen concentrations. Respiration of bacteria grown anaerobically was 30 to 40% of that of bacteria grown aerobically. Glucose decreased respiration of other substrates in both aerobically and anaerobically grown organisms. No cytochrome a 1 was present after anaerobic growth. Cytochrome c 1 was repressed by glucose; under anaerobic conditions this repression was antagonized by nitrate.

SUMMARY: Conidia of Penicillium expansum are covered with a surface layer of polyphosphate when grown on a high phosphate medium. The composition of this polyphosphate layer, which appears 2 days after conidial initiation, is dependent on the phosphate content of the growth medium; the layer is absent from conidia grown on a low phosphate medium. The rodlet layer which lies beneath the polyphosphate is free of cutin and does not consist of a unique protein. The amino acid composition of the surface protein is, however, different from that of the total wall protein. The rodlet layer appears to be an integral part of the spore wall.

The pH--mobility curves of Penicillium conidia are constant and species-specific when the fungi are grown on defined media.

SUMMARY: Cultures of a plus and a minus strain of Blakeslea trispora, grown either separately or together in light, accumulated only 40% of the β-carotene of corresponding cultures grown in darkness. The trisporic acids which accumulated in culture media of plus and minus strains grown together in light differed in their extinction spectra from the trisporic acids in the medium of cultures grown in darkness. Exposure of a trisporic acid extract from dark-grown cultures to light altered its extinction spectrum and decreased its carotenogenic activity. Only the ultraviolet portion of the spectrum of the lamps employed brought about this change in the extinction spectrum of the trisporic acid extract. The visible portion of the spectrum, however, was able to depress β-carotene accumulation in cultures without bringing about a change in the extinction spectrum of the trisporic acids produced. It seems likely that the formation of trisporic acids with altered extinction spectra is not responsible for the decrease in the accumulation of β-carotene.

SUMMARY: Spontaneous formation of macroscopic aggregates of yeast cells is termed flocculation. Many papers have been written on the subject (for reviews see Comrie, 1952, Gilliland, 1957; Jansen, 1958; Rainbow, 1966; Windisch, 1968), but because of the importance of the phenomenon to the brewer most of the studies have been confined to brewer's yeast. An analogous phenomenon in a fission yeast is described here.

Schizosaccharomyces pombe ncyc 132 was grown in 125 ml. Erlenmeyer flasks each containing 10 ml. malt-extract broth (Oxoid, 2%, w/v). The inoculum consisted of 5 × 106 stationary-phase yeast cells from a 24 h. static culture in the same medium in a tightly capped McCartney bottle. Cultures were shaken on a rotatory shaker at 150 rev./min. at 32°; the generation time was 120 min.