Alkali-metal ions in the metabolism of Bact. lactis aerogenes. I. Experiments on the uptake of radioactive potassium, rubidium and phosphorus

By the use as tracers of 42 K, 86 Rb and 32 P it has been shown that in the metabolism of Bact. lactis aerogenes ( а ) the alkali-metal ion enters the cell during oxidation of the carbon substrate (glucose, succinic acid, acetic acid), whether or not a nitrogen source is provided, so that growth occurs; in either event the alkali-metal ion subsequently leaves the cell again; ( b ) if the pH is lowered the maximum uptake of the cation by the functioning cell is raised, although increased hydrion concentration first causes displacement of alkali-metal ions from resting cells; ( c ) in the early stages of growth, or of glucose oxidation without growth, the flow into the cell of alkali cations and of phosphate anions takes place in a parallel way.

Studies on the mechanism of acetate oxidation by bacteria. VI. Comparative patterns of acetate oxidation by citrate-grown and acetate-grown Aerobacter aerogenes

The data presented in this paper indicate operation of different mechanisms for acetate oxidation by A. aerogenes, depending on the carbon source used for growth. The mechanism for citrate-grown cells appears to involve a conventional citric acid cycle, whereas acetate-grown cells appear to incorporate acetate carbon more readily via a dicarboxylic acid cycle.

Alkali-metal ions in the metabolism of Bact. lactis aerogenes. III. General discussion of their role and mode of action

The experimental findings described in parts I and II and previous work in the literature lead to certain conclusions about the role of alkali-metal ions in the growth and metabolism of Bact. lactis aerogenes . The view is favoured that the positive alkali-metal ions accompany negative phosphate ions into the cell during metabolism and that potassium or rubidium ions are of a size suitable for incorporation into a structure involving phosphorylated intermediates and enzyme surfaces. As long as a binding of this type persists there can be an automatic displacement of hydrions from the cell, which is therefore to some extent protected against their action. The mechanism, however, by which the cell is able to grow at a rate almost independent of pH over a wide range involves also adaptive changes in the proportions of enzymes.

Oxidation-reduction processes in cultures of bacteria. I. The reducing power of Bact. lactis aerogenes

Cultures of Bact. lactis aerogenes show a reducing power towards oxygen (as measured by a modification of the Thunberg methylene-blue test) which is a rather stable characteristic of the growth under specified conditions. During adaptation of cells to utilize a given carbon substrate the reducing power and the growth rate increase in parallel (over considerable ranges) to their respective optima. In general the reducing power of fully adapted cultures is nearly constant for a considerable variety of carbon sources (12 to 15 units) in spite of a nearly fourfold variation of optimal growth rates. The regularity is masked with certain substrates by abnormal enhancements or inhibitions occurring at high concentrations but reappears when the measurements are made in the low concentration range. The result suggests that there is normally a rate-limiting step in the part of the cell mechanism which consumes molecular oxygen. This is not altered by adaptation to a new carbon source, though when the cells are first transferred to a new medium the proportions of various enzymes are unsuitable for the optimum utilization of the substrate, and the amount of oxygen which can be consumed is far below the maximum. Until these proportions are finally readjusted growth rate and the degree to which the oxidizing mechanism can be used increase in parallel, a limit to the adaptive process being set by the relatively unchanging maximum oxygen uptake.

The resistance of Bact. lactis aerogenes to proflavine (2:8-diaminoacridine). I. The applicability of the statistical fluctuation test

The number of colonies ofBact. lactis aerogenesappearing on solid media containing proflavine (2:8-diaminoacridine) under different conditions has been determined. The statistical variation is greater with samples taken from different cultures than with the same number taken from a given culture. This might appear to correspond to the Luria-Delbrück criterion that the resistant colonies are formed from spontaneously appearing mutants in the cultures under test. It is pointed out, however, that this greater variation may in the present example depend equally well upon other factors than mutations, since separate cultures cannot be so closely controlled as any single culture in respect of age, pH and degree of aeration. The effects of these factors are studied, and it is shown that varying efficiency of aeration has a specially marked influence on the number of resistant survivors. It is shown, moreover, that there is a competition between the development of resistance and death of the population, and that the times at which the last surviving cell in a proflavine culture can be detected itself shows a very great variation. Thus the variation in the colony number can be a function of survival rather than of mutation. The form of the curve showing the initial decline of population followed by growth of resistant survivors is difficult to reconcile quantitatively with a simple form of the mutation hypothesis.

Alkali-metal ions in the metabolism of Bact. lactis aerogenes. II. Connexion with viability, growth rate and enzyme activity

The viability of Bact. lactis aerogenes is uninfluenced by deficiency of potassium in the medium. The dehydrogenase activity towards glucose is less affected by an adverse pH when there is sufficient supply than when there is a deficiency of this ion. The deaminase activity towards asparagine or alanine is equally dependent on the pH in both cases. Maximum growth rates (in a glucose medium) are independent of pH over a range where the glucose dehydrogenase activity drops markedly, but decreases in this latter activity can be to a considerable extent compensated for if the cells are allowed to take up potassium or rubidium ions (as shown by experiments with 86 Rb). Protective response to an adverse pH seems to involve two factors, first, an absorption of alkali-metal ions associated with intermediates in the oxidation of the carbon substrate, and secondly, adaptive changes accompanying growth.

Variations in catalase activity during a bacterial growth cycle

The variation in the relative rate of catalase synthesis byBact. lactis aerogeneshas been studied by measuring the enzyme activity of samples of cells taken at intervals from growing cultures, under different conditions. In the normal growth cycle in a glucose-ammonium sulphate medium the rate of catalase synthesis is small during the early part of the logarithmic phase, but the content per cell increases rapidly as the pH of the medium falls. The increased activity is not a direct result of the acidity itself, but may be attributed to modification of the cell metabolism under acid conditions so that more catalase is required. Continued growth under anaerobic conditions tends to reduce catalase activity, although the characteristic variation of the relative rate of synthesis through the growth cycle is maintained. The variation of the rate of formation of the enzyme in cells growing in a succinate medium is similar to that in glucose, although synthesis is now appreciable even in the early stages of growth.

Extracellular accumulation of pyrroles in bacterial cultures

Aerobacter aerogenes, Paracolobactrum aerogenoides, Spirillum serpens, and gelatinous strains of Chromobacterium violaceum produced an extracellular, ether-soluble, Ehrlich-positive substance when grown in media prepared with gelatin hydrolysate. The substance has been tentatively identified as pyrrole-2-carboxylic acid. Both hydroxy-l-proline and allo-d-hydroxyproline have been shown to be precursors of the material. Gelatinous strains of Chromobacterium violaceum, but not the other positive cultures, produced two ether-insoluble pyrroles as well, the precursors of which occur in gelatin hydrolysate but have not yet been identified. The property of pyrrole formation in bacteria and its possible use as an aid in identification of bacteria was discussed.

METHOD FOR THE DETECTION OF SIGNIFICANT BACTERIURIA IN LARGE GROUPS OF PATIENTS

A measured area of blotting paper was used as a vehicle for transferring a constant aliquot of urine on to the surface of a culture medium. The number of bacterial colonies growing in the inoculum area of the medium corresponded to the number of organisms in the urine. One thousand, two hundred and seventy-five urines from women attending an ante-natal clinic were tested by this method, and the results compared with the results of quantitative bacterial counting and of triphenyl tetrazolium chloride (T.T.C.) tests. The method was found to be a simple, cheap, and reliable way of screening urine specimens for significant bacteriuria.

THE DEVELOPMENT OF RESISTANCE TO TERRAMYCIN BY BACT. LACTIS AEROGENES (AEROBACTER AEROGENES)

The relation between the concentration of Terramycin and the lag preceding growth has been determined for the unadapted strain and for strains of Bact . latics aerogenes (Aerobacter aerogenes) fully adapted to a range of concentrations of drug. The family of curves so obtained, whose horizontal spacing can be predicted by a simple mathematical expression, shows that the resistance is continuously graded to the ‘training’ concentration. After one subculture in a low concentration of drug the resistance declines gradually, on growth in drug-free medium, to a state intermediate between full resistance and sensitivity and remains in this state for at least 500 generations in the absence of drug. Longer ‘training’ in which secondary effects of the drug occur results in a more stable resistance. Time-number relations for colony formation on solid media containing Terramycin show that no fully resistant forms exist in the original population. These responses are interpreted in terms of a competition between lethal and adaptive processes, and the changes in the macromolecular composition of the cells during the first subculture in liquid medium containing Terramycin are in accord with this.

ACTIVITY OF AMPICILLIN IN VITRO COMPARED WITH OTHER ANTIBIOTICS

Comparative tests in vitro for antibacterial activity were carried out with ampicillin, tetracycline, and chloramphenicol using 673 clinical isolates of Gram-negative bacilli and Streptococcus faecalis. Further comparative tests were also carried out with ampicillin, chloramphenicol, colistin sulphate, colistin methane sulphonate, cycloserine, kanamycin, nitrofurantoin, polymyxin, streptomycin, and tetracycline, using groups of 20 strains of each of the main species selected at random from the total number of isolates. Of the total number of isolates a higher percentage was inhibited by ampicillin than by tetracycline or chloramphenicol. Ampicillin showed particularly high activity against certain species of bacteria and displayed an antibacterial spectrum not shown by any of the other antibiotics tested.

ACCUMULATION OF INORGANIC POLYPHOSPHATE IN AEROBACTER AEROGENES. II. ENVIRONMENTAL CONTROL AND THE ROLE OF SULFUR COMPOUNDS

Harold, F. M. (National Jewish Hospital, Denver, Colo.) and Susan Sylvan. Accumulation of inorganic polyphosphate in Aerobacter aerogenes. II. Environmental control and the role of sulfur compounds. J. Bacteriol. 86:222-231. 1963.-The accumulation of inorganic polyphosphate in Aerobacter aerogenes was shown to be a function of the growth medium. In low-phosphate medium, polyphosphate accumulated whenever nucleic acid synthesis ceased due to a nutritional deficiency, regardless of its nature. In high-phosphate medium polyphosphate accumulation was induced only by sulfur starvation. Polyphosphate accumulation could thus be induced or suppressed at will by manipulation of the sulfur and phosphorus content of the medium. The specific requirement for sulfur starvation was traced to the presence of an intracellular inhibitor of polyphosphate accumulation. This was depleted during sulfur starvation and replenished when sulfate was restored. The inhibitor was identified as oxidized glutathione or a closely related compound. Suppression of polyphosphate accumulation required the simultaneous presence of a high exogenous phosphate concentration and a high intracellular glutathione level. Suppression of polyphosphate accumulation resulted in a constant polyphosphate level, due to a steady state of polyphosphate synthesis and degradation. The former continued at half the original rate while the latter was sharply accelerated. The synthetic and degradative phases of polyphosphate metabolism could be completely dissociated by inhibitors of energy generation. It is proposed that the primary effect of glutathione plus phosphate is the stimulation of polyphosphate degradation. Polyphosphate synthesis appears to be a general consequence of the inhibition of nucleic acid synthesis, but net accumulation may be obscured by concurrent degradation.

IN VITRO BIOLOGICAL ACTIVITY OF CEPHALOTHIN

Chang, Te-Wen (Tufts University School of Medicine, Boston, Mass.) and Louis Weinstein. In vitro biological activity of cephalothin. J. Bacteriol. 85:1022-1027. 1963.-Cephalothin is a "broad-spectrum" antibiotic active, in low concentrations, against Diplococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus. Shigella, Salmonella, and Proteus mirabilis were the most sensitive of the gram-negative organisms. Escherichia coli and Aerobacter aerogenes were suppressed to a lesser degree, whereas Pseudomonas aeruginosa and Herellea were highly resistant. Penicillin-sensitive and -resistant strains of S. aureus were equally susceptible to cephalothin. Exposure to increasing concentrations of the drug very frequently led to the development of resistance in gram-negative organisms; this was observed less often with S. aureus. Cephalothin stimulated the production of penicillinase by staphylococci, which remained sensitive to the cephalosporanic acid derivatives despite repeated subculture in increasing concentrations of the agent. Cephalothin was not inhibited by penicillinase. This antibiotic was more toxic to cultures of human amnion and mouse embryo cells than benzyl penicillin G but was less injurious than oxytetracycline, chlortetracycline, and demethylchlortetracycline; tetracylcine produced about the same degree of cellular damage as cephalothin.

ACCUMULATION OF INORGANIC POLYPHOSPHATE IN AEROBACTER AEROGENES. I. RELATIONSHIP TO GROWTH AND NUCLEIC ACID SYNTHESIS

Harold, F. M. (National Jewish Hospital, Denver, Colo.). Accumulation of inorganic polyphosphate in Aerobacter aerogenes. I. Relationship to growth and nucleic acid synthesis. J. Bacteriol. 86:216-221. 1963.-Growing cells of Aerobacter aerogenes contain traces of inorganic polyphosphate, but large amounts often accumulate when growth ceases as the result of a nutritional deficiency. The reciprocal relationship between growth and polyphosphate accumulation was traced to competition between nucleic acid synthesis and polyphosphate for intracellular phosphorus. Polyphosphate accumulated only after nucleic acid synthesis had ceased. Resumption of nucleic acid synthesis (with or without concurrent cell growth) induced rapid degradation of the polyphosphate with transfer of the phosphorus to ribonucleic acid (RNA). At the same time, incorporation of P(32) into polyphosphate was reduced, though not abolished. Competition for adenosine triphosphate may be part of the explanation. In addition, it appears that polyphosphate degradation is accelerated under conditions which permit rapid nucleic acid synthesis, the phosphorus released being trapped in RNA.