- Volume 129, Issue 1, 1983

The effect of cyanide on the physiology of lactate- and oxygen-limited Enterobacter aerogenes NCTC 10336 was studied in chemostat culture (D = 0·1 h−1). In the absence of cyanide, the molar growth yield from oxygen (Y O2) under oxygen limitation was 60% of the carbon-limited value. A similar decrease in yield was observed in a lactate-limited culture (excess oxygen) which was continuously fed low concentrations of potassium cyanide. The cultures with the lower growth yields possessed respiratory systems less sensitive to inhibition by cyanide. This was particularly marked in cultures grown in the presence of cyanide. Increased cyanide resistance was associated with an increase in the concentration of a cytochrome oxidase tentatively identified as a d-type and the appearance of additional cytochromes tentatively identified as b-type.

Several mutants of Bacillus subtilis were isolated which sporulate continually during exponential growth in glucose medium. The spdA1 mutation, responsible for the continual sporulation of one of the mutants, mapped near thr. When an exponentially growing culture of a strain containing spdA1 was maintained at essentially constant turbidity, 5% of the viable cells contained heat-resistant spores. The continual sporulation depended on the stringent response since it was absent in spdA relA double mutants. Genetic and biochemical analysis indicated that the continual sporulation of spdA1 strains was associated with a lower specific activity of pyruvate carboxylase, which limited the rate of oxaloacetate synthesis from glucose via pyruvate and thereby the supply of compounds depending on the citrate cycle, especially aspartate. Therefore, the mild stringent response caused by the spdA1 mutation seems to result from a partial deficiency of aspartyl-tRNA which may exert its sporulation-initiating effect during a limited time interval in each growth cycle. A mutant blocked in fumarase activity (citG) behaved similarly. It grew only slowly in glucose medium because much of the limiting oxaloacetate was wasted for the excretion of fumarate. The mutant produced little aspartate and sporulated at a high frequency in glucose medium, even in the presence of glutamate; the sporulation was again prevented by aspartate or malate or by introduction of the relA marker into the strain.

Inulase production by Kluyveromyces fragilis on various fermentable and non-fermentable carbon sources was examined in carbon-limited continuous culture. Fructose and sucrose supported superior inulase yields [above 24 μmol sucrose hydrolysed min−1 (mg cell dry wt)−1 at pH 5·0, 50 °C], while some other carbon sources, including lactose, galactose, ethanol and lactate, did not stimulate inulase formation beyond basal levels. Thus fructose was identified as the primary physiological inducer. Isolation of a constitutive mutant also provided genetic evidence for the inducible nature of inulase in the wild-type. The mutant was generated spontaneously and selected in continuous culture. It produced high inulase activities in continuous culture irrespective of the carbon source. Inulase formation in the wild-type and mutant strain was further controlled by general carbon catabolite repression as suggested by enzyme yield patterns in batch and continuous culture.

When Saccharomyces uvarum was cultivated in continuous culture, it exhibited the typical growth behaviour of a glucose-sensitive yeast. Metabolic changes related to glucose-repressed growth were assessed by an analysis of overall culture parameters (biomass formation, ethanol and acetate production and gas exchange rates) and by measuring the mitochondrial cytochrome content. These functions were mainly affected by the glucose effect; the steady state values of these variables were first established in the chemostat as a function of dilution rate.

The short- and long-term regulation taking place when the cells were submitted to repression was assessed by administering glucose pulses and by shifts in the dilution rate. The primary response of the cells to the initiation of repressed growth was the formation of ethanol and acetate. Since there was no repression of oxygen uptake rate or cytochrome content prior to this response, it was concluded that ethanol and acetate formation was not the consequence of repression of respiratory activity, but resulted from the regulation of pyruvate dehydrogenase and pyruvate decarboxylase activities. Long-term adaptation of the cells occurred within 24 to 48 h of the initiation of repressed growth as manifested by a decrease of mitochondrial cytochrome content to the steady state value corresponding to that of repressed growth.

Time-dependent changes in the intracellular Na+/K+ ratio of Escherichia coli, induced by the nitrofuran derivative HN32 [2,4-diamino-6-(5-nitrofuryl-2)-5-ethylpyrimidine], were measured by laser-induced mass spectrometry of single bacterial cells. The results show good agreement with data on viable cell and total cell counts, release of ATP and 14CO2 production demonstrating that the single cell analysis of intracellular sodium and potassium concentrations may supply reliable information on cell viability and, furthermore, offer additional information not available from established gross methods.

Light has been shown to affect aggregation and founder cell development in the cellular slime mould Polysphondylium violaceum. An aggregation-stimulating factor, D factor, also affects aggregation of P. violaceum wild-type and aggregation-defective mutants in the complementation group aggA. Both light and D factor cause premature aggregation of amoebae and increase the number of aggregate centres formed. In addition, D factor is able to stimulate aggregation of wild-type amoebae at densities where aggregation would not normally occur. Several experiments show that amoebae are more sensitive to D factor in the presence of light, with optimum aggregation occurring in the presence of both light and D factor. Development of founder cells has been observed in the aggA mutants in the absence of D factor. However, these founder cells are inactive and do not produce aggregates until D factor is added. This class of inactive founder cells can be detected in wild-type amoebae. Production of D factor is also dependent on light with a 20- to 60-fold decrease in production over that occurring in darkness. A complex relationship between D factor, light and founder cell differentiation is established by this study.