- Volume 128, Issue 8, 1982

mutant of Salmonella typhimurium with undetectable phosphoribosylpyrophosphate (PRPP) synthetase activity in vitro and abnormally low PRPP pools in vivo was identified by screening temperature-sensitive isolates by an autoradiographic procedure. The lack of PRPP synthetase activity in vitro and temperature-sensitive growth were shown to result from separate, but closely linked mutations mapping at 47 units on the Salmonella chromosome. Mutant cell extracts prepared by a variety of methods did not show any detectable PRPP synthetase activity, but material that was immunochemically cross-reactive with PRPP synthetase was detected by complement fixation analysis. A second mutant, isolated by localized mutagenesis, contained about half the PRPP synthetase and cross-reacting material of the parental strain.

A plasmid (pSV1) of 110 × 106 daltons from a methylenomycin A producing strain of Streptomyces violaceus-ruber was detected on and isolated from agarose gels. Elimination of this plasmid by protoplasting and regeneration resulted in the simultaneous loss of methylenomycin A production and resistance. pSV1 hybridized with pBR322 containing a cloned fragment of 1.7 × 106 daltons from S. coelicolor A3(2) which codes for methylenomycin A resistance. The pSV1 plasmid could be transferred to S. lividans by conjugation and by transformation and plasmid DNA identical in size to pSV1 could be isolated from the recipient strains. These experiments show that pSV1 codes for methylenomycin A production and resistance, in close analogy to the SCP1 plasmid from S. coelicolor A3(2).

Under sporulation conditions, Bacillus subtilis mutant SE63 secreted into the medium an inhibitor of the extracellular DNAase that is specifically associated with stage II to III of sporulation. The inhibitor was a heat-labile protein with a molecular weight of 18000–20000. A cell-bound, presumably intracellular, inhibitor with the same properties was found in extracts of wild-type cells and of the mutant. The mechanisms by which the mutation, designated din, might cause the secretion of a protein that is normally intracellular are discussed. The mutation was mapped by transduction with phage PBS1 and it lies between met and fru. It was also introduced into a variety of sporulation mutants including some blocked at the earliest known stages of the process. In all of these it caused secretion of the inhibitor. It is concluded that the secretion is therefore not integrally associated with sporulation but is, instead, part of the response of the cells to the nutritional step-down conditions in which spore formation is induced.

Four mutants of Escherichia coli K12 were isolated on the basis of their sensitivity to pH 5·4. Under non-permissive conditions their growth was reversibly inhibited. At pH 7·0 these mutants showed a highly pleiotropic phenotype, which included altered phage and detergent sensitivities and leakage of periplasmic proteins. The findings suggest a defect in the outer membrane, perhaps in lipopolysaccharide. Two mutants mapped in or near the rfa locus, while the other two were remote from this region.

Benzoate uptake in Pseudomonas putida is mediated by an active transport system capable of accumulating benzoate against a 150-fold concentration gradient when subsequent metabolism is blocked by mutation. Initial benzoate transport rates are inhibited by CCCP, sodium azide, arsenate and DCCD. Uptake is stimulated by including a respirable carbon source during preincubation of the bacteria. The initial uptake rate and the ATP pool levels are not correlated and no periplasmic components were found to bind benzoate. These observations indicate that benzoate uptake is energized by the membrane potential, rather than by ATP hydrolysis.

A species of Rhodococcus was isolated from garden soil on the basis of its capacity to use acetonitrile as sole C and N source. Acetonitrile-grown cells hydrolysed a number of amides and nitriles to ammonia. The substrate nitriles, listed in order of decreasing hydrolysis rates, were acetonitrile, acrylonitrile, propionitrile and n-butyronitrile. The corresponding amides were also hydrolysed together with formamide and, to a small extent, nicotinamide. With the exception of acrylonitrile and acrylamide, each compound supported growth as did the non-substrates malonamide, benzamide, α-phenylacetamide and 3-aminopropionitrile. Benzonitrile, phenylacetonitrile (benzyl cyanide), malononitrile and aminoacetonitrile did not support growth. Nicotinamide and benzamide stimulated acetamidase activity but malonamide had no effect. Both the aminonitriles inhibited the acetonitrilase system. Cells grown in succinate (NH4)2SO4 medium did not hydrolyse acetonitrile or acetamide indicating that the enzymes involved in nitrile degradation are subject to induction/repression. Acetamide and acetate appear to be gratuitous inducers of acetonitrilase: acetate also induces the acetamidase.

SMg2+-limited growth of the cyanobacterium Anacystis nidulans was investigated in batch and chemostat cultures. In batch cultures the growth rate of the organism depended on the Mg2+ concentration up to 5 μm. Although the maximum growth rate was achieved at this concentration, the organism formed aseptate filaments of three to four times the‘normal’ cell length. About 90 min after increasing the Mg2+ concentration from 5 μm to 1 mm the cell size decreased, followed by an increase in the division rate, which lasted for about 60 min and resulted in a 66% increase in cell number. The rates of DNA, RNA and protein synthesis were not altered during these Mg2+ shift-up experiments, showing that the control by Mg2+ of growth had been separated from its control of cell division, In Mg2+-limited chemostat cultures, the mean cell volume decreased from about 2·0 to 0·6 μm3 when the Mg2+ concentration was increased from 2·5 to 10 μm. This increase in Mg2+ also resulted in an increase in the calculated intracellular Mg2- concentration from 27 to 78 mm, and the amount of cellular Mg2+ bound in chlorophyll increased from 17 to 22%. A comparison of Mg2+-and SO4 2−-limited chemostat cultures showed that the mean cell volume decreased with increasing dilution rate when Mg2+ was the limiting factor, whereas it increased with dilution rate when SO4 2− was limiting. Only small differences in the rates of RNA and protein synthesis were found in the two cultures, although the synthesis of RNA was Mg2+-dependent. The ratio of total RNA to protein, which gives the amount of RNA necessary to synthesize one protein unit (RNA efficiency), was independent of the growth rate in both SO4 2−-and Mg2+-limited chemostat cultures showing that the efficiency of culture RNA was variable in both cases. The efficiency was higher under SO4 2−-than Mg2+-limited conditions.

Out of 19 strains belonging to the family Enterobacteriaceae only Escherichia coli and Citrobacter strains fermented fumarate exclusively to succinate. This fermentation was dependent on the presence of molecular hydrogen or formate. The inability of these micro-organisms to convert fumarate to succinate, acetate and CO2 correlated with their lack, or low activity, of oxaloacetate decarboxylase.

Continuous culture experiments were performed with Citrobacter freundii in minimal or complex medium with fumarate + H2 or formate, and the growth parameters were determined. From the data obtained, a Ymaxfumarate dissimilated max value of 10·5 ± 0·8 g dry wt per mol fumarate dissimilated was calculated. This value demonstrates that, per mol fumarate reduced, at least 0·6 ± 0·05 mol ATP is produced and subsequently used for biosynthetic purposes.

Twenty alkalophilic actinomycetes with optimum growth pH of 9·0 to 9·5 were isolated. Although these new isolates morphologically closely resembled conventional streptomycetes containing ll-diaminopimelic acid, nine out of 20 isolates contained meso-diaminopimelic acid.

Among 420 International Streptomyces Project (ISP) Streptomyces strains tested for their maximum growth pH, only 6 strains grew at pH 11·5. Of these six strains, three strains, S. caeruleus ISP 5103, A. alborubidus ISP 5465 and S. autotrophicus ISP 5011 contained meso-diaminopimelic acid.

Naturally grown fruit-bodies of Suillus luteus, S. bovinus and S. variegatus were subjected to Py-GC. The pyrograms obtained were statistically analysed and classified with a multivariate classification program (SIMCA). The class describing the S. bovinus pyrograms was significantly separated from both the S. luteus and the S. variegatus classes, while these two classes showed some over-lapping which was due to variation between different fruit-bodies within each species. The taxonomic significance of the statistical distances between the classes representing the species is uncertain.