- Volume 132, Issue 9, 1986

Summary: The effect of the nitrogen source on the activity of ferredoxin-dependent nitrite reductase has been studied in the cyanobacterium Anacystis nidulans. De novo synthesis of nitrite reductase occurred in the absence of an added nitrogen source, although enzyme activity was higher when the medium contained either NO3 − or NO2 −. The positive effect of NO3 − on nitrite reductase was also evident in tungstate-treated A. nidulans, which lacked an active nitrate reductase, indicating that the stimulatory effect was due to NO3 − itself and not to the NO2 − resulting from its intracellular reduction. NH4 + acted as a repressor, overriding any positive effect of NO3 − or NO2 −. Nitrite reductase synthesis was freed from NH4 + repression by l-methionine-DL-sulphoximine, an irreversible inhibitor of glutamine synthetase. NH4 + must therefore be metabolized through glutamine synthetase before repressing nitrite reductase. The kinetics of nitrate reductase and nitrite reductase development were similar in cells transferred from NH4 +- to NO3 −-containing media, suggesting a coordinate regulation of synthesis.

Summary: Four strains of the thermophilic phototrophic green bacterium Chloroflexus aurantiacus were tested for nitrogenase activity under a variety of nutritional conditions consistent with nitrogenase derepression in anoxygenic photosynthetic bacteria. Although all strains of C. aurantiacus could grow with various amino acids as sole nitrogen sources, no growth on N2 was observed; acetylene reduction was undetectable in cells grown under any nutritional conditions. The inability of Chloroflexus to fix N2 is discussed in connection with its thermophilic character.

Summary: Mycelial fungi generate endogenous electrical fields which are associated with polarized tip growth. Here we show that applied electrical fields can dramatically affect the polarity of growth of a variety of filamentous fungi including Neurospora crassa, Aspergillus nidulans, Mucor mucedo, Trichoderma harzianum and Achlya bisexualis. The precise behaviour of each fungus when exposed to an electric field was different; however the sites of germ tube formation and branching, the direction of hyphal extension and the frequency of branching and germination could all be affected. N. crassa and Ach. bisexualis grew and formed branches towards the anode while Asp. nidulans and M. mucedo exhibited tropisms towards the cathode. Galvanotropism of hyphae and branches of T. harzianum was in opposite directions. Germ tube formation from conidia of N. crassa was highly polarized in electrical fields whereas fields of a similar strength had little effect on the polarity of germ tube formation in Asp. nidulans. Hyphae became aligned perpendicularly as they grew longer and as the field strength increased. It is suggested that this perpendicularly orientated extension relieves growth-inhibiting perturbations of the membrane potential in cells which had been aligned parallel to the field. These results are discussed in relation to the hypothesis that the polarity of hyphal growth is under electrical control.

Summary: Ethanol and other substances that induce rhizomorphs in Armillaria spp. also induced laccase formation. In a range of isolates rhizomorph production and laccase activities were positively correlated. Laccase was first detectable just before the appearance of rhizomorph initials. Its activity reached a peak when rhizomorph growth rate was highest and fell to near zero when rhizomorph growth ceased. Laccase was not detected in non-induced cultures. Laccase reaction with chromogenic substrates was much higher in rhizomorphs than in mycelia. Laccase activity and rhizomorph production, but not mycelial growth, were decreased in the presence of enzyme inhibitors with activity against laccase. The results suggest a role for laccase in morphogenesis and/or growth of rhizomorphs.

Summary: Among the spheroidal fission-yeast (Schizosaccharomyces pombe) cells resulting from aculeacin A treatment were found cells whose putative growth axis and polarity differed from those of their progenitor, that is they were changed in the orientation of their septum. The ratio of cell length (measured perpendicular to the septum plane) to septum diameter of these cells equalled or exceeded unity without exception, whether the septum orientation changed or not and whether the cellular shape was spherical, spheroidal or cylindrical. From these results we conclude that the septum is always oriented perpendicular to the plane including the longest axis of the cell even if the morphology is irregular or the new septum has become perpendicular to the previous septum. There is no cellular region forbidden to new septa.

Summary: Twelve strains of Streptococcus mutans serotype c were grown in batch culture with glucose at constant pH (6.0) and a number of properties compared. On the basis of their cellular and extracellular protein profiles, the strains were divided into three groups, I, II and III, containing five, four and three strains, respectively. The extracellular protein profiles for a particular strain differed if the organisms were grown either at pH 6.0 with fructose instead of glucose or with glucose but without pH control. The total amount of extracellular protein produced by group III strains grown in glucose-containing medium at pH 6.0 was several times that produced by strains of groups I and II, which were also more hydrophobic. One of the potentially important proteins is P1, also called antigen B or I/II, and it was shown to be entirely in the culture fluid of group III strains but mostly cell-associated from strains of groups I and II. Approximately half of the cell-associated fraction of P1 could be removed with hot sodium dodecyl sulphate.

Summary: A novel enzymic activity, responsible for the conversion of mannopine to agropine by lactonization, has been identified in Agrobacterium strains. This activity is encoded by octopine-type and agropine-type Ti or Ri plasmids, and is inducible by mannopine and agropine. In crude extracts it is stable for long periods and can be used for preparative synthesis of agropine from mannopine. The physiological role of this activity is not understood. However, it is probably involved in degradation of opines of the agropine family since it is always associated with agropine utilization in wild-type strains.

SUMMARY: The requirement for gluconeogenesis and the pentose phosphate pathway in sporulation of Saccharomyces cerevisiae was investigated using homozygous diploids with mutations in selected portions of the respective metabolic pathways. Mutations affecting the genes FBA1 (fructose-1,6-bisphosphate aldolase), GPM1 (phosphoglycerate mutase) and ZWF1 (glucose-6-phosphate dehydrogenase) were used. Homozygous diploids bearing either fba1-11 or gpm1 mutations were asporogenous, indicating an absolute requirement for gluconeogenesis in sporulation. A strain homozygous for the zwf1 mutation sporulated, but at a reduced level compared to the wild-type. Homozygous spd1-1 mutations restored the ability to sporulate in fbal-11 homozygous diploids; this is believed to occur as a consequence of reduced NH+ 4 levels in spd1-1-bearing strains, the reduced intracellular NH+ 4 content serving to promote gluconeogenesis via the residual low levels of enzyme activity present in such mutants.

Summary: Streptomyces sp. MA406-A-1 produced formycin (a nucleoside antibiotic) in parallel with cell growth in a synthetic medium. When the synthetic medium was supplemented with 1% (w/v) Casamino acids, however, formycin was produced only after the end of exponential growth. The intracellular ppGpp pool increased gradually towards the end of exponential growth and was maximal at the beginning of formycin production. After shift down from Casamino acids medium to synthetic medium, the ppGpp pool increased immediately, while the GTP pool decreased; under such conditions, the ability to produce formycin increased eightfold. Relaxed (rel) mutants, the first isolated for a Streptomyces species, were found at high incidence (10%) among spontaneous thiopeptin-resistant isolates and had severely reduced abilities to accumulate ppGpp. These rel mutants also failed to produce formycin under the usual culture conditions and exhibited numerous pleiotropic effects such as an inability to produce melanin and an extended delay of aerial mycelium formation. Thus Streptomyces sp. exhibited a typical stringent response, and the response initiated (or was needed for) the induction of secondary metabolism. The response may have also participated in the initiation of aerial mycelium formation by decreasing the intracellular GTP pool.

Summary: UV-induction of prophage P78 of Acinetobacter calcoaceticus increased with the UV-dose given to the lysogenic strain from the spontaneous induction frequency of about 0.8% to a maximal frequency of 10%. This 10- to 20-fold increase of induction frequency, as measured by the number of infective centres, was accompanied by a 1000-fold increase in the yield of free phage. This effect was probably due to an increase in burst size under the conditions of lysogenic induction. Unusually, the lysogen was more resistant to UV-irradiation than the corresponding non-lysogenic strain.