Showing papers in "Journal of Bacteriology in 1952"

Replica plating and indirect selection of bacterial mutants

Abstract: Elective enrichment is an indispensable technique in bacterial physiology and genetics (van Niel, 1949). Specific biotypes are most readily isolated by the establishment of cultural conditions that favor their growth or survival. It has been repeatedly questioned, however, whether a selective environment may not only select but also direct adaptive heritable changes. In accord with similar discussions in evolutionary biology (Huxley, 1942), we may denote the concepts of spontaneous mutation and natural selection in contrast to specific induction as \"preadaptation\" and \"directed mutation\", respectively. Many lines of evidence have been adduced in support of preadaptation in a variety of systems (Luria and Delbruick, 1943; Lea and Coulson, 1949; Burnet, 1929; Newcombe, 1949; Lewis, 1934; Kristensen, 1944; Novick and Szilard, 1950; Ryan and Schneider, 1949; Demerec, 1948; Welsch, 1950; also reviewed: Braun, 1047; Luria, 1947; Lederberg, 1948, 1949). This paper concerns an approach to this problem that makes use of a replica plating technique which facilitates the handling of large numbers of bacterial clones for classification on a variety of media.

Genetic exchange in salmonella

Abstract: Genetic investigations with many different bacteria have revealed parallelisms and some contrasts with the biology of higher forms. The successful application of selective enrichment techniques to the study of gene recombination in Escherichia coli (Tatum and Lederberg, 1947; Lederberg et al., 1951) suggestred that a similar approach should be applied to other bacteria. This paper presents the results of such experiments with Salmonella typhimurium a.nd other Salmonella serot,ypes. The mechanism of genetic exchange found in these experiments differs from sexual recombination in E. coli in many respect’s so as t,o warrant a new descriptive term, transduction.

A nonhereditary, host-induced variation of bacterial viruses.

Abstract: In this article, Luria reported that some bacteria, when infected with phage, would modify the phage in such a way so that it cannot reproduce in that particular bacteria type. However, the variation gives the phage the ability to infect a different bacterial species, in this instance Shigella. This is the first instance of the phenomenon of restriction and modification that would soon after be explained by the discovery of restriction enzymes in bacteria. Luria's work with Human, which described bacterial restriction-modification systems, eventually led to the discovery of restriction enzymes.

The effect of certain cultural factors on production of dextransucrase by Leuconostoc mesenteroides.

Abstract: Present knowledge on the characteristics of dextransucrase and its mode of action is based primarily on the important investigations of Hehre (1941, 1946, 1951) and Hehre and Sugg (1942). Hitherto, a serious impediment to studies of this interesting enzyme has been the difficulty of procuring dextransucrase. Development of further knowledge about it would be greatly facilitated by the availability of culture liquors rich in dextransucrase. The rapid formation of dextransucrase in high yields has been reported in a preliminary note (Koepsell and Tsuchiya, 1952). The present report deals in greater detail with our observations on factors affecting production of dextransucrase from Leuconostoc mesenteroides, strain NRRL B-512.2 However, culture liquors high in activity have been obtained from a large number of the organisms tested. The dextran produced by strain NRRL B-512 in the conventional whole culture procedure contains about 95 per cent a-1,6-glucopyranosidic linkage. Although the non-1,6 linkages have been assumed to be of the a-1,4 type, definite proof on this point is lacking (Jeanes and Wilham, 1950). L. mesenteroides, strain NRRL B-512, or its substrains, is the organism principally used in investigations of clinical dextran in the United States. Although the term \"dextransucrase\" is used in the singular for convenience, the possibility that more than one enzyme may be involved in the synthesis of dextran is recognized.

Resistance to ultraviolet light as an index to the reproduction of bacteriophage

Abstract: Infection of a susceptible bacterium by a single phage particle initiates a series of events climaxed, after a time called the latent period, by bursting of the cell and the release of a number (burst size) of replicas of the initial phage. We are here concerned primarily with the intervening process of phage replication which takes place behind the cloak of the cell wall. By prematurely disrupting infected cells, 'Doermann (1948) found that infective phage replicas are already present well before the time at which the bacterium bursts, i.e., about two-thirds of the way through the latent period. At earlier times, however, no plaque-forming particles are recovered, not even the initial phage. Our attention is, therefore, focused upon this \"dark\" period, during which the infecting phage must undergo some modification, and the key processes of phage reproduction come to pass. Luria and Latarjet (1947) conceived the following experiment in an attempt to use target theory for an analysis of the intracellular developments. It had been shown by Anderson (1948) that a bacterium (Escherichia coli, strain B) could be subjected to rather heavy doses of ultraviolet light and still survive in its ability to support the growth of phage T2. Thus, if one were to infect cells of strain B with single particles of T2 and irradiate the phage-bacterium complexes, the survival of infectivity (the ability to release at least one phage particle, thereby forming a plaque) of the complex should be determined by the survival of the phage part. If the irradiation is done immediately after infection, one should obtain the same survival curve for complexes as for the free phage irradiated before addition to bacteria, i.e., an approximately exponential or \"onehit\" curve. If complexes are allowed to develop to the point where several intracellular phage particles are present, the inactivation of the complex requires at least one \"hit\" in each phage, and a multiple-target survival curve should be obtained. The set of curves for samples irradiated at different stages in the latent period would be expected to resemble the theoretical curves of figure 1. These multiple-target curves, plotted on a semilogarithmic graph, are characterized by asymptotes of constant slope equal to that for the single phage particle. The intercept of the asymptote, extrapolated to zero dose, corresponds to the logarithm of the number of targets.

On the culture and general physiology of the green sulfur bacteria.

Abstract: Green sulfur bacteria were first obtained in pure culture and studied under controlled conditions by van Niel (1930, 1931). He isolated several strains which, on the basis of their morphology, were identified as Chlorobium limicola Nadson (1912). Physiologically the species was characterized as strictly anaerobic, obligatorily photosynthetic, requiring H25 for growth. The sulfide was quantitatively oxidized to sulfur with concomitant reduction of C02. The asimilatory process could be approximately expressed by the equation:

Growth and hydrogenase activity of a new bacterium, Hydrogenomonas facilis.

Abstract: The elucidation in nonsulfur purple bacteria of the parallelism between the hydrogen donors for photosynthesis and for heterotrophic growth helped clarify bacterial photosynthesis and photosynthesis in general (van Niel, 1949). Further comparative studies on the fixation of CO2 by autotrophic bacteria and here, in particular, by a hydrogen bacterium should further the understanding of how CO2 is assimilated in photosynthesis. Two ways of posing the problem of CO2 fixation in hydrogen bacteria are: how is hydrogen utilized? and what is the connection between hydrogen assimilation and heterotrophic growth? This paper reports some cultural characteristics of a new autotrophic hydrogen bacterium and describes its highly active hydrogenase.

Enzymatic synthesis of dextran

Abstract: CurTent events have intensified interest in blood plasma substitutes. Partially hydrolyzed dextran is under study in many laboratories for this purpose. The parent substance, \"native\" dextran, is a glucose polymer in which a-1 ,6-glucopyranosidic linkages predominate, and is produced by growing Leuconostoc mesenteroides or other suitable bacteria on media containing sucrose. Hehre (Science: 93, 237, 1941), Stacey (Nature: 149, 639, 1942), and others have obtained it by use of cell-free preparations of dextransucrase, the dextran-synthesizing enzyme, elaborated by these organisms. Partial hydrolysis of native dextran is necessary to reduce the molecular size from several millions to approximately 75,000 as desired for its use as a plasma substitute. Preliminary experiments with cell-free dextransucrase preparations have suggested that the molecular size of the dextran produced can be varied by modifying reaction conditions, and dextran of proper size for clinical use might be obtainable by direct synthesis. Large scale use of an enzymatic process for the production of dextran requires simple and economical production of highly potent enzyme preparations. This note will describe certain cultural factors which have recently been found to lead to rapid formation of dextransucrase in high yield in a medium suitable for industrial production of the enzyme. Although this report deals only with enzyme preparations from L. mesenteroides, strain NRRL B-512, active enzyme preparations have been obtained from many strains of L. mesenteroides and other organisms. The high sucrose levels commonly used in the production of dextran lead to viscous cultures from which separation of bacterial cells is difficult. We have found that low sugar concentrations obviate this difficulty without seriously curtailing high yields of dextransucrase. A cell-free enzyme preparation is obtained simply by centrifuging or filtering the cultures. The nitrogen and other nutrient requirements of the organism can be satisfied by corn steep liquor and mineral salts. Dextransucrase potency of the enzyme preparations is assayed by measuring the amount of fructose produced, as determined by the copper-reduction method of Somogyi (J. Biol. Chem., 160, 61, 1945), in a given time under ideal reaction conditions. The assay reaction mixture contains 10 per cent sucrose, M/20 acetate as buffer at pH 5.0, and the enzyme, and is held at 30 C. Enzyme potency is proportional to fructose production, providing that less than one-half of the sucrose has been utilized. One dextransucrase unit is defined as the amount of enzyme which will convert one mg of sucrose in one hour under these conditions. A cultural factor critically affecting enzyme yields is close control of pH of

The effects of a tryptophan-histidine deficiency in a mutant of Escherichia coli.

Abstract: Cells placed in a favorable environment are capable of duplicating themselves indefinitely. This implies that the over-all reaction rates of each of the synthetic systems must be balanced as every component of the cell is duplicated in the same timeinterval. It is evident that the various systems must be somehow coupled together since completely independent systems could not maintain these balanced rates in various environmental conditions. Thus, a coupling between the carbohydrate metabolism and synthetic activities is demonstrated by the decrease in oxygen uptake when nitrogen is removed from the medium. At the same time there is a degree of independence among the various metabolic systems. For example, carbohydrate metabolism proceeds at a reduced rate even though growth is stopped by lack of nitrogen. Also, certain ion deficiencies have more pronounced effects on some synthetic activities than on others. We have attempted to examine the degree of coupling among the various systems by observing the metabolism of mutant cells of Escherichia coli which were prevented from duplicating by the lack of one or more required amino acids. This deficiency would be expected to block protein synthesis, but the immediate effect on other systems, in particular nucleic acid synthesis, could not be predicted. Radioactive carbon, sulfur, and phosphorus were utilized as indicators of synthesis; growth and respiration were observed by the usual techniques. On completing these experiments it became apparent that the method utilized in this work might also be of value in determining the mode of action of various rtoisons and antibiotics.

Studies on antibiotic synergism and antagonism. Synergism among seven antibiotics against various bacteria in vitro.

Abstract: In an increasing nuimber of microbial infections of man, treatment with single antibiotics fails to cure. Some of these infections, however, respond favorably to combined treatment with two antibiotic drugs. Certain pairs of these drugs have proved successful in a limited number of clinical situations. An outstanding example is the frequent cure of bacterial endocarditis due to enterococci by the simultaneous administration of penicillin and streptomycin, whereas neither of these drugs alone cures more than a small number of cases (Hunter, 1950; Robbins and Tompsett, 1951; Cates, Christie, and Garrod, 1951). The synergism of penicillin and streptomycin in vitro is manifested by a marked increase in the bactericidal rate beyond that obtainable with any concentration of either drug alone and also by the killing of the entire exposed bacterial population, a feat which neither of the two drugs can achieve alone (Jawetz, Guinnison, and Coleman, 1950; Gunnison, Jawetz, and Coleman, 1950). As more microorganisms which are resistant to certain antibiotics are encountered in medical practice, there is an increased temptation to employ more than one antimicrobial drug routinely. Such indiscriminate use of two drugs is probably inadvisable inasmuch as antagonism between certain antibiotics has been demonstrated both in vitro and in experimental animals (Jawetz, Gunnison, Speck, and Coleman, 1951; Speck, Jawetz, and Gunnison, 1951; Jawetz, Gunnison, and Speck, 1951). To obtain a rational basis for the selection of antibiotics for combined therapy it is essential that the relationships among these drugs be studied. This report deals with some quantitative relationships in several synergistic combinations of antibiotics active against a number of different bacteria. The results may contribute clues to the mechanism of combined antibiotic action. An attempt has been made to answer some of the questions which arise as to the combined effect of two antibiotics in vitro.

A study of the incidence of Pseudomonas aeruginosa from various natural sources.

Abstract: The seeming ubiquity of Pseudomonas aerumtnosa ramses the question as to its normal habitat. This organism has been isolated from soil, animal feces, water, and many other sources. The aquatic and soil habitat of the pseudomonads as a group suggests water or soil as a possible habitat, and many species of Pseudomonas can be isolated from these sources. Some species are plant pathogens, and a few may be animal pathogens. Many standard texts list various sources for this organism, but there seems to be very little or no information about sources from which it can be isolated with sufficient consistency so that they can be considered, in part at least, the natural habitat of the organism. This raises the question as to whether the animal infections represent invasion of the body by organisms that naturally occur elsewhere with a nonparasitic mode of existence, or whether these infections result from invasion of the tissues by organisms that are usually parasitic in the intestinal tract or elsewhere in the body. The following investigation was made in order to determine those sources from which P. aeruginosa could be isolated with the greatest regularity and coincidentally to study some of the identifying characteristics of this microorganism.

Mutual exclusion between related phages.

Abstract: The discovery of the breakdown of superinfecting phage needs to be supplemented by genetic tests to find out whether the phage whose nucleic acid is broken down is, indeed, unable to contribute genetic markers to the progeny. The present paper presents experiments of this kind, whose results leave no doubt that the breakdown of superinfecting phage is strictly paralleled by exclusion from the progeny of the genetic markers it contains. We are presenting also some experiments in which the stimulating phage alone or both the stimulating and the superinfecting phage have been inactivated by irradiation with ultraviolet light. These experiments serve to characterize functions which have remained unimpaired in ultraviolet treated phage and their relation to multiplicity reactivation of ultraviolet treated phage.

A cobalt-containing medium for sporulation of streptomyces species

Abstract: prepared from cultures grown by the method of Dolman (Can. J. Pub. Health, 27, 489, 1936) and were heat-treated to destroy alpha and beta toxins. The filtrates were applied to the sciatic nerve of the frog, Rana pipiens, after the nerve had been removed from the animal together with the attached gastrocnemius muscle. The muscle was secured between a muscle clamp and the recording arm of a kymograph, leaving one end of the nerve free for application of filtrate. Application of a toxic filtrate to the free end of the nerve created an immediate reaction which caused peaks to be produced on an otherwise straight line recorded on the smoked drum of the kymograph. Nontoxic filtrates produced only the straight line effect. All of the 93 strains of S. aureus had, at the time of isolation, met the biochemical criteria for pathogenic staphylococci. After nine months in stock culture only seven strains still met these criteria. This group of seven, as well as the five strains with a history of food poisoning and a record of having produced symptoms in monkeys, reacted positively by the kymographic technique. Eightysix strains of S. aureus and one strain of S. albus were negative. Likewise, the sterile medium, its components, and Ringer's solution for cold-blooded animals gave negative reactions. The filtrates created a reaction only when they were applied to the nerve. Bathing the muscle tissue with filtrate produced no response. Once a nervemuscle preparation had been mounted on the kymograph, it could be used a number of times as long as it was bathed thoroughly between tests with Ringer's solution. Tetanus toxin, used for control purposes, produced results on the kymograph identical to those obtained with staphylococcal filtrates. Whether the neurotoxic substance present in S. aureus filtrates is identical to gastroenterotoxin has not been established, but the symptomatology of staphylococcal food poisoning strongly suggests involvement of the nervous system. A detailed account of the procedure employed in the kymographic technique is soon to be published.

Further observations on the change to virulence of bacteriophage-infected avirulent strains of corynebacterium diphtheriae

Abstract: It was recently reported from this laboratory (Freeman, 1951) that virulent strains of Corynebacterium diphtheriae were isolated from avirulent C. diphtheriae cultures which had been exposed to diphtheria bacteriophage. The studies described here establish the reproducibility of the original results, starting, however, from single cell cultures. Other observations suggest the immunologic identity of the original avirulent and derived virulent strains, and demonstrate the absence of preformed toxin in the avirulent strains, and of \"true\" lysogenicity in the derived virulent strains.

Factors affecting the lytic activity of lysozyme

Abstract: Since the initial discovery of lysozyme by Fleming (1922), nuimerous attempts have been made to describe the properties of this enzyme. The absence of a reliable method for the determination of enzymatic activity, however, has contributed to the incompleteness and to the inconsistency of the facts found in the literature. The availability of crystalline, egg white lysozyme has made it possible to study quantitatively some of the factors which affect its lytic activity. The assay method reported by Smolelis and Hartsell (1949) has been found to be accurate and highly adaptable to the study of this enzyme. This report concenms its application to the effect of pH, salts, ions, temperature, and manner of preparation of the cell suspension, on the activity of lysozyme.

Selectivity of sorbic acid media for the catalase negative lactic acid bacteria and clostridia

Abstract: A wide variety of media have been used to grow lactic acid bacteria (Ayers and Mudge, 1920; Barber and Frazier, 1945; Kulp, 1927; Kulp and Rettger, 1924; Mickle and Breed, 1925; Mobley, 1937a,b,c, Norris et al., 1950; Orla-Jensen, 1919, 1943; Pederson, 1929; Pelczar and Vera, 1949; and Weiss and Rettger, 1934, among others). However, in the experience of the authors, these media have, in many instances, failed when they have been used to enrich, enumerate, or isolate lactic acid bacteria found together with yeasts, molds, and other bacteria in various food product samples. These media do not selectively favor the growth of the lactic acid bacteria; consequently, the other microorganisms also present in the sample may outgrow them. Colonies of yeasts and other bacteria frequently may be mistaken for lactic acid bacteria when plate "counts" are made. Therefore, the advantages to be gained from a medium which would favor the growth of the lactic acid bacteria but inhibits all other microorganisms would be considerable. Attempts to develop such a medium were made. The use of different substrates and combinations of substrates with required nutrients was tried with alteration of physical conditions (pH, atmosphere, and temperature). These exploratory experiments, made over a period of years, were of little value. On investigation of inhibitory compounds added to conventional media it was noted that sorbic acid selectively favored the growth of Lactobacillus and Leuconostoc strains and inhibited all of the other test cultures of bacteria, molds, and yeasts (Vaughn and Emard, 1951).1 This observation confirmed, in part at least, earlier observations made by Gooding (1945) and Phillips and Mundt (1950) concerning the inhibitory properties of sorbic acid. It also stimulated further attempts to develop a medium which would be useful for enrichment and presumptive identification of the lactic acid bacteria. The results of these latter investigations are described in the following pages.

Dextran-degrading enzymes from molds.

Abstract: Enzymes capable of degrading dextran, the polymer of glucose produced from sucrose by the action of Leuconostoc mesenteroides and related organisms, are potentially valuable for fundamental research as well as for practical application. Although the a-i ,6-glucopyranosidic linkage is present to the extent of 95 per cent or more in some easily obtainable dextrans, the only other known occurrence of this linkage is the 5 to 10 per cent found in starch, glycogen, and similar polysaccharides. Thus, as has been pointed out previously by Jeanes et al. (1948), dextran provides a unique source of simpler carbohydrates containig the a-1 ,6-glucosidic linkage obtainable through enzymic degradation. Enzymes produced by organisms grown on dextran and capable of cleaving the 1,6 linkage may be useful in studies concerning starch structure. And lastly, as has been indicated already by Ingelman (1948) and by Whiteside-Carlson and Carlson (1952), 'ther types of dextranases offer a means for degrading dextran to molecular size range suitable for use as synthetic blood volume expanders. Although in this paper the term \"dextranase\" is used in the singular, we recognize the possibility of there being more than one enzyme that degrades dextran. Furthermore, a microorganism may produce more than one type of dextran-depolymerizing enzyme. There are reported here our observations on the occurrence, production, and activity of certain mold enzymes that degrade dextran from Leuconostoc mesenteroides, strain NRRL B-512, to diand higher oligosaccharides. This dextran is a linear type which contains approximately 95 per cent a-i, 6-glucosidic linkages (Jeanes and Wilham, 1950). In our search for dextran-hydrolyzing enzymes, begun in 1945, we have screened approximately 200 strains of bacteria, yeasts, and molds for their ability to produce extracellular dextranase. Like van Tieghem (1878), Colin and Belval (1940), and others, we were unable to find organisms producing large amounts of the enzyme among bacteria and yeasts. Ingeiman (1948) has reported a low order of dextranase activity from Cellvibrio fulva. Recently, Hehre and Sery (1952) have isolated dextran-splitting anaerobic bacteria from the h an intestine. Independently of Hultin and Nordstr6m (1948, 1949), we found that certain strains of Penicillia produced extracellular dextranase, but in small amounts. However, when we tested the species of Penicillia used by Hultin and

The effects of certain purines and pyrimidines upon the production of riboflavin by Eremothecium ashbyii.

Abstract: Eremothecium ashbyii is one of a number of organisms which produce considerable amounts of riboflavin, most of which is secreted by the cells into the medium (Guilliermond, 1935). The investigations of Schopfer (1944) and Schopfer and Guilloud (1945) resulted in the development of a synthetic medium for this organism which permitted growth and riboflavin production to occur under chemically defined conditions. Subsequent studies by Yaw (1948) have led to a modification of the original medium to iiZclude the amino acids, methionine and histidine. With the determination of the nutritional requirements of E. ashbyii, it became possible to undertake studies concerning the mechanism of riboflavin biosynthesis by means of precursors which modify riboflavin yield. Such an approach was utilized by Yaw (1948), who tested certain synthetic compounds for precursor activity. However, none of the compounds tested was found to be active in the biosynthesis of riboflavin. The present study is concerned with the purines and pyrimidines in the biosynthesis of riboflavin by E. ashbyii. These compounds were selected for the following reasons: (1) There are marked similarities in chemical structure among the purines, pyrimidines, and riboflavin, all of which contain a diazine ring, and (2) the purines and pyrimidines are naturally occurring compoun$ds. It was therefore hoped that the information obtained would provide a better understanding of riboflavin biosynthesis, about which very little is known at present (Williams et al., 1950).

Degenerative processes in a strain of Clostridium butylicum.

Abstract: The butyric acid forming bacteria, if continuously subcultured, undergo certain changes which affect morphological as well as physiological features. These changes were described as early as 1893 by Grimbert as degenerative changes of his cultures. Winogradsky (1902) found that his Clostridium pasteurianum ceased to form spores or clostridial forms in subcultures, and that growth was mainly in the form of long chains of vegetative cells. The rate of fermentation decreased, and the strain lost its ability to fix nitrogen and finally died out. Bredemann (1909) stated that none of his 30 strains could be maintained by direct subculture for any length of time. Continuous cultivation was possible only by the regular use of spores as inoculum. References to this process have continued to appear in the literature until recent years. However, in spite of the early recognition of this phenomenon and its obvious theoretical and practical importance, no detailed study of the degenerative process itself is found in literature. It is our aim in this work to describe in detail the process of degeneration as it occurs in consecutive cultures; and, if possible, to determine the external and internal factors differentiating these degenerate cultures from their parent cells.

The properties of x-ray inactivated bacteriophage.

Abstract: The rate at which X-ray irradiation inactivates bacteriophage particles, that is, destroys their ability to reproduce, has been shown to depend on the medium in which the virus particles are suspended (Luria and Exner, 1941). Phage suspended in a solution of inorganic salts is inactivated at a faster rate than in nutrient broth, and the more rapid inactivation is interpreted as being due largely to chemical agents produced in the surrounding medium by ionizations outside the phage. Some components of the nutrient broth must act as protective substances. The chemical basis for the protective action has been analyzed by several workers, among them Dale (1942), Luria and Exner (1941), and Latarjet and Ephrati (1948), who found that small concentrations of many substances such as tryptophan, thiourea, glutathione, and gelatin give complete protection. It is generally believed that the protective nature of these substances is due to their competing with the virus particles for the toxic agents produced in the medium. In the presence of an excess of most protective substances there remains a residual nonprotectable inactivation, whose rate is independent of the temperature during irradiation and of the intensity of the irradiation. The nonprotectable inactivation is generally considered as due to a direct effect of X-rays, that is, to acts of absorption of X-ray energy within the phage particles (Luria and Exner, 1941). In support of the idea of \"direct\" action is the finding that the X-ray sensitivity of different phages in nutrient broth increases with the particle size as determined by ultrafiltration (Wollman and Lacassagne, 1940; Luria and Exner, 1941). The logarithm of the survival ratio is inversely proportional to the dose; the particle size could be estimated relatively accurately by assuming that every cluster of ionization produced within a particle resulted in inactivation. Wollman, Holweck, and Luria (1940) found that a given amount of ionization was less effective if produced by alpha particles than by X-rays, as expected if inactivation resulted from ionizations produced within the phage particles. Ionizations produced by alpha particles are more closely packed than those produced

The isolation and characteristics of a spirochete from the bovine rumen.

Abstract: A small spiral organism has been observed repeatedly in the rumen contents of cattle. These observations have been made by direct microscopic examination (Hastings, 1944; Baker, 1943) and through the use of culture techniques (Hungate, 1947; Sijpesteijn, 1948). During the course of the present investigation similar organisms were found in the rumen of all cattle examined. A close examination showed that it was actually a spirochete. The ease with which it could be cultivated made it particularly suitable for further study, and the paucity of experiments on the physiology of spirochetes made it seem profitable to investigate the characteristics of this strain from the rumen.

A critical test of the recombination theory of multiplicity reactivation

Abstract: Precise survival curves for phage production by bacteria multiple infected with phage T2 inactivated by ultraviolet light have been determined for a wide range of ultraviolet doses, with and without photoreactivation. The results are not compatible with the recombination theory, according to which multiplicity reactivation is due to a recombination of undamaged units from several parental particles.

Respiratory activity of cell-free extracts from azotobacter.

Abstract: It is now clear that in most animal tissues that have been thoroughly investigated the main pathway of terminral respiration takes place via the citric acid cycle as developed by Krebs (1940), Green et al. (1948), and others. The mechanism of oxidative reactions of bacteria, however, is still confused because of the lack of sufficient experimental data and the presence of conflicting reports. For example, Karlsson and Barker (1948) reported that cells of Azotobacter agile did not metabolize acetic acid via the pathway of the cycle and suggested that some unknown mechanism may be involved. Ochoa (personal communication) has found, however, that extracts of this organism contain the enzyme that condenses acetate to citrate. Ajl (1950) presented evidence of the citric acid cycle in the metabolism of Escherichia coli and Aerobacter aerogenes but believes that an additional oxidative pathway such as a C2-C2 condensation may also function. Recently Foulkes (1951) has shown that although yeast cells did not metabolize added tricarboxylic acids, cell-free extracts can be obtained capable of oxidizing these acids at a rate approaching 40 per cent of the rate for pyruvate oxidation by the intact cells. The respiration of Azotobacter is of particular interest because this organism has the highest rate of oxidation (based on cell dry weight or nitrogen) of any microorganism yet reported and because its oxidative metabolism is related to nitrogen fixation. Azotobacter vinelandii, strain \"original\", was selected for this study as dehydrogenase activity had been demonstrated in cell-free extracts from this organism by Lee, Burris, and Wilson (1942).

A note on Pseudomonas stutzeri.

Abstract: During the two decades following the discovery of the denitrification process several notable papers were published on the isolation and characterization of denitrifying bacteria. A study of this literature reveals that Burri and Stutzer (1895) were the first to describe such organisms in sufficient detail to render them recognizable. This applies particularly to their Bacillus denitrificans II, an organism of wide distribution and outstanding characteristics, which has been isolated from straw, manure, soil, canal water, etc., and which students of the denitrification process have considered as a very common and easily identifiable denitrifier. Nevertheless, this species has been neglected in virtually all American literature dealing with systematic bacteriology, and in the most recent and authoritative treatise on the subject, the 6th edition of Bergey's Manual (Breed et al., 1948), it now can be found in an appendix to the genus Achromobacter with the notation: \"Many of the following species were described before Gram and flagella stains had been perfected. Hence it is impossible to identify them definitely as belonging to Achromobacter. Comparative study is needed in other cases before the remaining species can be placed in their proper place in the genus.\" (p. 422). There is no justification for this attitude with respect to Burri and Stutzer's Bacillus denitrificans II. As the following account will show, the misconception may be ascribed to a number of factors, among which we mention specifically: (1) a strange confusion in the nomenclatorial status of the bacterium in question; (2) an error in judgment on the part of Migula; (3) a general lack of interest after 1905 in organisms causing denitrification; and (4) unfamiliarity with the species and with the pertinent literature on the part of some American workers. It is the contention of this essay that Burri and Stutzer's Bacillus denitrificans II should be restored to its position of prominence under the name Pseudomonas stutzeri.