- Volume 115, Issue 1, 1979

During nitrogen deprivation, de novo synthesis of glutamine synthetase was induced in non-growing conidia of Neurospora crassa. When ammonia or glutamine was added to conidia which had been deprived of nitrogen, glutamine and arginine accumulated at a higher rate than in condia not deprived of nitrogen. The degradation of exogenous glutamine to glutamate is apparently a necessary step in the accumulation of glutamine and arginine within the conidia. In non-growing conidia, a cycle probably operates in which glutamine is degraded and resynthesized. The advantages of such a cycle would be that the carbon and nitrogen could be used to synthesize amino acids in general, as well as for the synthesis and accumulation of arginine and/or glutamine in particular.

A diaminopimelate-requiring mutant of Bacillus megaterium was shown to lack the enzyme N-acetyl-ll-diaminopimelate deacylase. By repeated subculture of this mutant, a second-stage mutant was derived that could grow slowly in minimal defined medium supplemented with dd-diaminopimelate alone. After growth in such medium, the peptidoglycan of the wall still contained mainly meso- and ll-diaminopimelate; radioactivity from dd-diamino-[14C]pimelate entered peptidoglycan (as diamino[14C]pimelate) and protein (as [14C]lysine) to similar extents.

The production of carotenoid pigments by the yeast Phaffia rhodozyma depended on the culture conditions. Astaxanthin, the primary carotenoid in this yeast, was produced mainly during the exponential phase of growth. The concentration of carotenes in P. rhodozyma remained relatively constant [about 5 μg (g yeast)−1] throughout growth in a 1·5% (w/v) glucose medium, but the xanthophyll concentration increased from 90 to 406 μg (g yeast)−1 during fermentation. Active xanthophyll synthesis occurred during the period of accelerating growth and after exhaustion of glucose from the growth medium. In media containing more than 1·5% (w/v) glucose, however, yeast and carotenoid yields were considerably reduced. The pH of the medium affected yeast yields and carotenoid production; the optimum pH was 5·0. At pH 3·5, β-zeacarotene accumulated in P. rhodozyma. β-Carotene was the primary carotene in the yeast under all other conditions tested. The optimum temperature for yeast growth and pigment formation was 20 to 22 °C and the best carbon source was d-cellobiose. Oxygen was an important substrate for optimum yields of yeast and astaxanthin; under microaerophilic growth conditions, astaxanthin production was drastically decreased and P. rhodozyma accumulated β-carotene and the monoketone echinenone.

l-Alanyl-l-tyrosine and glycyl-l-phenylalanine labelled with 14C competed with each other and with the dipeptide antibiotic bacilysin for transport into Staphylococcus aureus NCTC 6571 in a medium which did not support growth. They also competed with other dipeptides and several tripeptides. The fast initial transport of the two labelled peptides appeared to show Michaelis–Menten kinetics. Neither was transported into a bacilysin-resistant mutant of S. aureus NCTC 6571, although tyrosine was taken up by the mutant as readily as it was by the parent strain.

Uptake of alanyltyrosine or glycylphenylalanine was followed by rapid hydrolysis of the peptide and the excretion of tyrosine or phenylalanine. Glycine liberated from glycylphenylalanine was partly degraded and partly incorporated into the bacterial wall. The behaviour of these dipeptides paralleled the inactivation of bacilysin by suspensions of S. aureus and the appearance of its C-terminal amino acid, anticapsin, in the extracellular fluid.

Summary: In amoebae of Dictyostelium discoideum the ribothymidine (rT) content of tRNA is 0·9 mol%, but decreases progressively during development into spores. To elucidate which nucleosides replace rT at position 54 in developmental tRNA we have characterized ‘vegetative’ and ‘developmental’ tRNAs from the slime mould. Specific tRNAs were separated by two-dimensional gel electrophoresis. During early developmental stages, all tRNA species that could be separated by this method were newly synthesized. A new tRNA with uridine in place of rT and having an electrophoretic mobility similar to ‘vegetative’ tRNAAsn was detected during the early preaggregation stage. This ‘developmental’ tRNA was also extracted from purified polysomes. When development proceeds from preaggregation to postaggregation, tRNAs accumulate with 2′O-methylribothymidine in place of rT. We suggest that these developmental tRNAs are important for the synthesis of specific developmental proteins.

In strains of Bacillus subtilis able to synthesize purines de novo, massive sporulation is suppressed by the combination of excess ammonia, glucose and phosphate. Purine auxo-trophs, blocked in the general or the guanine-specific portion of the branched purine pathway, sporulated in such a medium when the purine required for normal growth was removed from the medium. The resulting spore titre and the sporulation frequency increased with the residual growth rate in the purine-free medium, i.e. with the leakiness of the purine mutation. Sporulation was further increased by allowing residual growth in growth-limiting amounts of guanosine. Non-leaky purine mutants blocked before 5′-phosphoribosyl-5-amino-4-imidazole carboxamide also sporulated well when supplied with 5-amino-4-imidazole carboxamide at concentrations (2 mm) that supported growth at a suboptimal rate.

Nitrate reductase activity was three to four orders of magnitude greater in freshwater sediments than in the overlying water. Viable (most probable number) counts of denitrifiers provided sufficient resolution to distinguish between anoxic and surface waters, and between these and sediments, but did not correlate with differences between or within sediment cores. Activity within the sediment depended on the electrode potential (E h) profile, which in turn was related to the degree of turbulence and oxygen concentration in the overlying water. Sediments from the littoral zone or those in contact with oxygenated water were oxidizing to a depth of 5 to 10 mm and the E h then decreased rapidly. In these sediments nitrate reductase activity was often at its maximum at a depth of 10 to 15 mm, on the E h gradient, and coincided with a mean E h value of 210 mV. Under reducing conditions theE h gradient moved upwards and nitrate reductase activity was greatest at thesediment-water interface. These observations were supported by analyses of the nitrogen gas content of the sediments. Inhibition of the enzymes with chlorate indicated that approximately 60 % ofthe activity was dissimilatory in sediments where the E h was greater than+100 mV, and that this proportion increased to more than 90 % when the E h fell below + 50 mV. Although the evidence was not conclusive, there was also some indication that nitrate reductase activity in aerobic surface sediments was greater in the larger (> 250 μm) particle size fraction, which suggested that these particles might act as microsites for nitrate respiration.

The microbiology of the benthos of 16 lakes in Cumbria was studied. The lakes formed a series ranging from oligotrophic to eutrophic, and the results were compared with other surveys of their chemistry and biology. The sediments of the more productive lakes contained more organic matter, E h measurements indicated that they were more reduced, and the overlying water was deoxygenated to a greater degree. These results correlated with greater microbial activity, biomass and numbers in the sediments of the richer lakes, as measured by electron transport system activity, ATP and direct counts. The data obtained from the sediments were, however, more variable, and showed poorer agreement with the assumed ranking of the lakes than the results obtained from the water column in this and past surveys. The microbiology of the benthos suggested that the more productive lakes might be considered as a distinct group, but more detailed sampling and careful choice of indicator micro-organisms would be required to provide statistically significant evidence for this.

According to Passow & Rothstein (1960), the mercury-induced loss of K+ from yeast cells is an all-or-none effect. This hypothesis was tested by analysing individual yeast cells by means of energy-dispersive X-ray microanalysis. A dual effect of mercury was observed. The cell population was split into two parts: one part consisted of cells that had suffered a (nearly) complete loss of K+ - the number of these cells increased with increasing concentrations of HgCl2; the other consisted of cells that had only lost part of their K+ content - these cells showed a normal distribution around a central value that decreased with increasing concentrations of HgCl2. Our analysis shows that the effect of mercury is more complex than originally suggested and that, in addition to an all-or-none effect, a gradual loss of K+ occurs.

Synchronous cultures of Escherichia coli B were produced under various environmental conditions. Analysis of the cell number data permitted the characterization of the generation time distribution for these organisms and the estimation of the mother-daughter generation time correlation coefficients. For all growth conditions, the distribution of generation times was found to be symmetrical with a coefficient of variation of 0·22±0·02. The mother-daughter generation time correlation coefficient was significantly negative at doubling times between 40 and 64 min. However, the results for a culture growing in succinate medium at 37°C, which had a significantly greater generation time, yielded a correlation coefficient close to zero. Within the range of temperatures studied (26 to 37°C), no significant effect on the correlation coefficient was observed.

A recently published mathematical model for mycelial growth and the initiation and growth of sporophores in the mushroom crop is extended to allow for harvesting of the sporophores. The extended model exhibits temporal fluctuations in yield which are similar, in most respects, to those produced by real crops. The response of the model to changes in the age at which sporophores are harvested is also similar to that observed experimentally, except that little change in total yield is predicted. It is suggested that this discrepancy is associated with the abortion of sporophore primordia, which is not allowed for in the model. The model is used to demonstrate the importance of using regular harvesting schedules in mushroom cropping experiments.

Escherichia coli W3110 was grown in a chemostat under conditions of carbon limitation at various temperatures and specific growth rates (μ). Exponential survivor-time curves following cold osmotic shock were biphasic. These could be described by the sum of two exponential functions representing the survival of sensitive and resistant fractions of the population where the size of the sensitive fraction was directly proportional to μ. Decimal reduction times for the more resistant fraction were unaffected by μ yet decreased with increasing growth temperature.

Sensitivity to cold shock was evaluated for an E. coli CR34 mutant, temperature-sensitive in initiation of DNA replication. When grown in the chemostat at the nonrestrictive temperature (30°C) sensitivity was directly proportional to μ . Following a rise in the incubation temperature to 42°C, sensitivity decreased markedly and reached a minimum 45 to 60 min after the temperature increase. Sensitivity of the E. coli mutant grown at 30°C and raised to 42°C for 1 h was low and relatively unaffected by growth rate.

The polyacrylamide disc gel electrophoretic pattern of five isoenzymes of phosphomono-esterases (both alkaline and acid) of Aspergillus nidulans has been established. Bands I and V are derepressible acid phosphatases, band II is constitutive acid phosphatase, band III a derepressible alkaline phosphatase and band IV a constitutive alkaline phosphatase. Isoenzyme III can be completely inhibited by p-fluorophenylalanine (FPA).

Experiments using FPA, cycloheximide and actinomycin D indicated that transcription for isoenzyme III (inhibited by actinomycin D) took place between 20 and 21 h incubation, and translation of the mRNA so formed occurred between 21 and 22 h. FPA and cycloheximide were both inhibitory at the time of translation. However, cycloheximide caused a gradual reduction in the quantity of all isoenzymes, whereas only isoenzyme III was affected by FPA. The different effect of FPA was confirmed by incorporation of radioactive FPA into isoenzyme III. FPA apparently did not inhibit synthesis of isoenzyme III, but inactivated the isoenzyme III formed in its presence.

Constitutive isoenzymes synthesized in the presence of FPA showed normal activity. It is suggested that FPA may not necessarily affect the activity of all proteins synthesized in its presence but whenever it is incorporated into indispensable sites in proteins, it inactivates them. This may be the mechanism of growth inhibition by FPA in Aspergillus nidulans.

Production of oospores by Phytophthora cactorum in media supplemented with ten ∆5-sterols, differing in the structure of their side chains, has been measured. Spore production increased with increasing size of the substituent at C-24: H < CH3 < C2H5. A 24β-methyl group conferred greater activity than a 24β-methyl, but there was less difference between ∆5-sterols with 24β- and 24β-ethyl groups. There was a greater difference between ∆7-sterols with 24α- and 24β-ethyl substituents. A double bond at C-22 had no effect on spore production when trans, but reduced activity when cis.

Four ∆7-sterols have been compared with their corresponding ∆5-sterols. Fewer oospores were produced at low concentrations (0·2 to 1 mg 1−1) of each ∆7-sterol than with the ∆5-sterol, but at higher concentrations (10 to 30 mg 1−1), the numbers with the ∆7-sterol bore no consistent relation to the numbers with the ∆5-sterol.

The difference between two sterols in promoting sexual reproduction in Phytophthora cactorum is not apparently related to differences in uptake into the mycelium, or to known effects on properties of membranes, but is believed to be due to differences in metabolism of the sterols, and to differences in the hormone activity of compounds derived from them.

Di- and tripeptides shared the same transport system in Saccharomyces cerevisiae. Typical rates of uptake were 1 to 5 nmol peptide min−1 (mg dry wt)−1; these rates were influenced by the composition and sequence of the peptide. Accumulation of intact sarcosine peptides was demonstrated. Rates of peptide uptake were essentially the same in the wild-type and in several amino acid permease-deficient mutants. These results were derived from application of two fluorescence methods that permit direct determination of peptide uptake.

The rate of oxygen uptake by single macroplasmodia of Physarum polycephalum increased in two steps during each synchronous mitotic cycle. Plateaux in the respiratory pattern, of 0·22 cycles duration, occurred in mid-interphase and in the period up to and including mitosis. A fall in the rate of respiration was frequently associated with mitosis itself. This pattern of respiration continued for more than 10 mitotic cycles after inoculation and was unaffected by omission of an initial routine period of starvation. A similar stepped pattern of respiration was observed in synchronously germinating spherules during the period between outgrowth and the first mitosis. The specific activities of succinate dehydrogenase, fumarase and malate dehydrogenase remained relatively constant during the mitotic cycle, while fluctuations in cytochrome oxidase activity paralleled those in specific respiratory activity. Possible mechanisms for controlling the pattern of respiration are discussed with reference to published data on protoplasmic streaming and ATP concentrations during the mitotic cycle.

Growth efficiency (c) and specific maintenance rate constant (μ e) were determined in continuous cultures of the cyanobacterium Oscillatoria agardhii Gomont, in light energy-limiting conditions, according to the formula μ = cq E-μ e in which q E is the specific light energy uptake rate. Values of the efficiency factor c varied with irradiance from 0·23 at 0·5 W m−2 to 0·05 at 40 W m−2. The specific maintenance rate constant was 0·001 h−1. The culture pH value influenced c and μ e . A diurnal light/dark cycle with a 16 h photoperiod did not affect either of the two parameters, μ e and c. The relationship between growth rate and light energy uptake rate, embodied in the above formula, was also valid for nitrogen (nitrate)-limited cultures.

Many sugars and derivatives were tested in the capillary assay for their attraction of Bacillus subtilis. The major attractants were 2-deoxy-d-glucose, d-fructose, gentiobiose, d-glucose, maltose, d-mannitol, d-mannose, N-acetylglucosamine, α-methyl-d-glucoside, β-methyl-d-glucoside, N-acetylmannosamine, α-methyl-d-mannoside, d-sorbitol, l-sorbose, sucrose, trehalose and d-xylose. Only glucose chemotaxis was completely constitutive. Competition experiments were carried out to determine the specificities of chemoreceptors. There were 25 instances of no influence of two sugars on each other’s taxis, 92 instances of one sugar interfering non-reciprocally with chemotaxis towards another and 49 instances of two sugars reciprocally competing. However, in most of the last instances, other sugars were identified that interfered with chemotaxis towards one member of the pair but not the other. Thus, nearly all sugars and related compounds appear to be detected by their own chemoreceptors, but many secondary interactions exist.

Alcaligenes eutrophus strain H16 when grown on formate or oxalate as the sole source of carbon and energy had doubling times between 3·5 and 4·5 h. The respective molar growth yields (Y m) were 2·35 and 3·9. During growth on formate or oxalate both a soluble and a membrane-bound formate dehydrogenase were formed. The key enzymes of autotrophic CO2 fixation, ribulose-5-phosphate kinase and ribulosebisphosphate carboxylase, were formed during growth on formate but not on oxalate. Oxalate induced the synthesis of the enzymes of the glycerate pathway. Mutants impaired in autotrophic CO2 fixation but unaffected in the synthesis of the formate dehydrogenases lost their ability to grow on formate but not to grow on oxalate, giving further evidence that formate was assimilated via CO2.

The inhibitory effect of l-lysine on penicillin biosynthesis by Penicillium chrysogenum has been compared in a low-producing strain (Wis. 54–1255) and a high-producing strain (AS-P-78). Lysine inhibited total penicillin synthesis to a similar extent in both strains. However, in the high-producing strain the onset of penicillin synthesis occurred even at a high lysine concentration, whereas in the low-producing strain lysine had to be depleted before penicillin production commenced.

Linoleic acid, but not stearic acid, inhibited the growth of Staphylococcus aureus NCTC 8325. Growth inhibition was associated with an increase in the permeability of the bacterial membrane. The presence of a plasmid conferring resistance to penicillin (PC plasmid, e.g. pI258 blaI−) increased the growth inhibitory and membrane permeability effects of linoleic acid. Under growth inhibitory conditions, linoleic acid was incorporated into the lipid of both PC plasmid-containing and PC plasmid-negative bacteria and there was little difference between these cultures in the uptake or fate of linoleic acid. Experiments using a glycerol auxotroph of S. aureus suggested that free linoleic acid, rather than lipid containing this acid, inhibits growth. Linoleic acid probably inhibits growth by increasing the permeability of the bacterial membrane as a result of its surfactant action, and the presence of the PC plasmid increases these effects.

Ten species of fungi were obtained from poultry droppings in Nigeria. Six of these are true thermophiles while the other four are thermotolerant. Aspergillus fumigatus Fresenius, Mucor pusillus Lindt and Thermoascus aurantiacus Stolk are known human pathogens. Except for M. pusillus, all the thermotolerant species had a higher occurrence at 45°C while the thermophilic varieties were readily obtained at 50°C.

Spores of the fission yeast Schizosaccharomyces pombe have been separated from vegetative cells by a simple and rapid centrifugation (800 g for 20 min) through a 35% Hypaque solution to a purity >95%. Approximately 35% of the spores were recovered. Regrowth in EMM2 plus glucose showed that over 97% of the spores germinated within the first 2 h and outgrowth continued between 5 and 10 h. Sucrose induced germination in > 95% of the spores with a 1 h delay and outgrowth in 50 % of the spores with a 3 h delay. There was little protein synthesis during germination but the protein content increased linearly coincident with outgrowth. The RNA content increased slightly during germination, but increased linearly 1 h before the onset of outgrowth and protein synthesis. After 8 h of regrowth, coincident with the onset of DNA synthesis, the rate of RNA synthesis was accelerated. The DNA content had increased 1·7-fold after 10 h of regrowth from a haploid level of 1·36 10−8 μg spore−1.