- Volume 39, Issue 1, 1965

The blue-green alga Chlorogloea fritschii fixed elementary nitrogen to a limited extent in the dark in a strictly inorganic medium. Growth and nitrogen fixation continued in the dark when a suitable organic substrate was present in the medium. Among the organic substrates tested, sucrose (0·01 m) was the most readily utilized and was outstanding in supporting nitrogen fixation in the dark. The alga was adapted to heterotrophic conditions after continuous incubation and repeated subcultivation in the dark. Inter-relations between carbon assimilation and nitrogen fixation under heterotrophic conditions were observed. Sucrose assimilation proceeded more vigorously in the light and resulted in a fourfold increase in the rate of growth and nitrogen fixation. Sucrose assimilation was increased in the light in the absence of carbon dioxide from the gas phase, but nitrogen fixation was greatest when the alga was supplied with sucrose and carbon dioxide. Carbon dioxide was inhibitory to sucrose assimilation and slightly to nitrogen fixation in the dark.

Methionine inhibition of the phenotypic expression of adn - → adn + reverse mutations in the fission yeast Schizosaccharomyces pombe was investigated. This inhibition occurred solely with L-methionine, and not with a variety of other growth factors. The inhibitory effect on revertant expression did not apply to a number of reverse and forward mutations other than adn - → adn +. Alteration of the adenine supply to adn - organisms before and after mutagen treatment had no effect. Methionine was shown to have additional inhibitory effects on the leakiness of an adn - mutant, on complementation between adn-1 mutants, and on the growth of certain adn - strains in the presence of the analogue 6-methyl-aminopurine. It is suggested that S-adenosylmethionine may be implicated in these methionine effects.

The wild-type strains of Neurospora crassa first isolated by Dodge, Abbott & Chilton were found to differ in the range of temperatures over which protoperithecia were produced; similar results were obtained with two recently isolated wild strains of a species of Neurospora. The ability to develop protoperithecia at 30° was found to be controlled by at least two genes in reciprocal crosses between two wild types differing in this character. A correlation of these observations with the reported features of tyrosinase production is discussed. Certain mutant strains backcrossed repeatedly to a wild-type strain gave exceptional results at 30°. Preliminary observations suggest that the part played by nicotinamide in the sexual cycle may be connected with some of these exceptions. Temperature did not obviously affect ascus development in outbred crosses between Lindegren and Abbott wild-type strains. With inbred crosses ascus development was controlled by several factors which were temperature sensitive and differed in degree of effect in reciprocal crosses. In most strains tested 20° was the optimum temperature for normal ascus development. At higher temperatures gross abnormalities were observed including asci with more than eight spores.

Two pathways for methionine methyl formation, one cobalamin-dependent and one cobalamin-independent, corresponding to those observed in Escherichia coli pa 15 have been found in Aerobacter aerogenes. An initial difficulty in showing the cobalamin-dependent pathway in cell-free extracts proved to be due to the presence of enzymes which caused the removal of adenosylmethionine, a cofactor required for this system. In contrast to E. coli pa 15, A. aerogenes contains holocobalaminmethyl-transferase even when grown in the absence of cobalamin. When cobalamin is added to the growth medium, the cobalamin-independent pathway is repressed.

Many different strains of Bacillus cereus and members of other species of the genus Bacillus were induced to lyse by exposure to the proper concentration of mitomycin C, a radiomimetic drug. For some bacilli, induction of lysis occurred only in Casamino acids containing medium but not in nutrient broth + yeast extract medium, whereas other bacilli showed the opposite behaviour. The efficiency of induction was a function of the growth phase of the culture and of the concentration of mitomycin C. Induction of lysis in B. thuringiensis resulted in the release of oedema factor and phospholipase into the medium. Mitomycin C-induced lysis of B. cereus was prevented by adding chloramphenicol, actinomycin D, or 5-fluorouracil deoxyriboside up to 40 min. later. There appeared to be no sequential loss of susceptibility to inhibition by these compounds as expected.

This paper describes some Neurospora mutants which grow on minimal medium when the gas-phase contains 30 % CO2 (v/v); they are referred to as ‘CO2 mutants’. One is an arginine mutant (arg-2; 33442) having a mutation at a different locus from the other arginine CO2 mutant (arg-3; 30300); a second (arg-11; 30820) requires arginine + a purine + a pyrimidine for growth in the absence of CO2; a third (44601) requires arginine + a purine + a pyrimidine + a carboxylic acid for growth in the absence of CO2. The mutations in mutants 30820 and 44601 are allelic and the carboxylic acid requirement of mutant 44601 is attributable to its genetic background. The remaining CO2 mutants described here were isolated directly from wild-type Neurospora, and their nutritional requirements in the absence of CO2 subsequently determined. Two of these mutants, which are allelic, are adenine-requiring mutants sited at the adenine-3 locus, although the adenine-3A and -3B mutants 38709 and Y 112-M2 are not CO2 mutants. Another two of these new CO2 mutants, which may be allelic, require carboxylic acids in the absence of CO2; these mutants are similar in their nutritional requirements to the succinate mutants described by Lewis (1948) and Strauss (1956) .

A new procedure for the removal of iron from complex media is given. With this method, the iron requirements for the growth of Staphylococcus aureus in casein hydrolysate medium were investigated. Trypticase medium (0·6–0·8 μg. Fe/ml.) was depleted of iron by treatment with the specific iron-chelator bathophenanthroline; on analysis it was shown to contain 0·01–0·02 μg. Fe/ml. Preliminary studies showed that S. aureus grew well in the iron-depleted medium. Further iron restriction of the already depleted medium was accomplished by the addition of conalbumin, a specific iron-chelating protein present in egg white. The initiation of growth, rate of growth, and total crop were all dependent on the concentration of free iron in the medium. The availability of iron was a function of the percentage iron saturation of the conalbumin.

Mitochondria isolated from protoplasts of conidia, young germinated conidia, and branched mycelia of Neurospora crassa, have an active oxidative phosphorylation system which showed no variation in the three stages of development studied ; succinate dehydrogenase also did not alter. Cytochrome oxidase activity showed a marked increase at the time of conidial germination; this was not maintained during further growth. An electron microscope study of the conidia showed them to have complex mitochondria analogous to those seen in older mycelial hyphae. A large accumulation of lipid material and extensive vacuolization was observed in these conidia. A rudimentary reticular system with numerous ribosomes lying free in this membrane system were observed. Macroconidia were usually multinucleate; up to 10 nuclei were observed. The outer conidial wall was completely digested by snail extract (Helix pomatia digestive juice) and was structurally identical with that of the hyphae as seen with the fixation and embedding conditions used.

The isolation and properties of 23 phages lytic for stalked bacteria of the genera Caulobacter and Asticcacaulis are described. They fall into seven groups on the basis of host range and serological properties. Phages of groups I–VI attack only Caulobacter species; those of group VII, only Asticcacaulis. Groups I–III comprise DNA viruses with long flexible tails and of unusually large size, the heads having dimensions of 50 × 170 mμ. Groups IV–VI comprise RNA viruses of simple structure, 21–23 mμ in diameter. The specific Asticcacaulis phages (group VII) are tailed DNA viruses, similar in form and size to coliphage lambda. The implications of this study for the taxonomy of the caulobacters are discussed.

The growth of individual organisms of four Gram-negative species has been measured. The growth rate of the individual was not in general constant, and its mean value differed from one organism to another in the same culture. There was positive correlation between the size of an organism at termination and the size of its mother at termination. These findings are contrary to the major postulates of the Koch & Schaechter hypothesis, but are so far no more than qualitatively established. Fission is unsymmetrical in respect of growth rate and size; the growth rate and size of sisters differ systematically according to their relative positions in the family tree.

From the intestinal tracts of 37 out of 69 birds belonging to four species of gulls (Larus fuscus, L. genei, L. argentatus, L. ridibundus) and three species of terns (Sterna sandvicensis, S. hirundo, S. minuta) 62 yeast isolates belonging to 16 species were obtained. The occurrences of individual yeast species were (% of positive birds in brackets): Saccharomyces cereυisiae (20%), Torulopsis glabrata (12%), S. oleaginosus (10%), Candida tropicalis (9%), C. albicans (9%) and T. pintolopesii (7%), other yeast species (1–4%). Average numbers of colony-forming units/g. wet intestinal contents in the seven host species were: Larus fuscus 5210; Larus genei 22,200; L. argentatus 5620; L. ridibundus 3180; Sterna sandυicensis 50; S. hirunda 211,000; S. minuta 9200.

Certain synthetic processes of a stable L-form and its parent streptococcus were compared to examine whether conversion was accompanied by significant alterations in the growth pattern. DNA and RNA were isolated from the streptococcus and its derived L-form, degraded, and molar base ratios measured and compared. Conversion to the L-form apparently did not result in a disturbance of synthetic processes related to DNA and RNA rates of syntheses and growth measured by extinction of cultures, colony count and dry weight increases. The stable L-form, although almost twice as slow growing, as compared with the streptococcus, retained the ability to function in an orderly manner and was capable of balanced growth. Conversion from streptococcus to L-form did not result in an addition to the DNA base complement (5-methylcytosine, 5-hydroxy-methylcytosine) nor in a quantitative alteration in the molar base ratio of either nucleic acid in the resulting L-form. The disorganization in L-form division characteristic of L-form growth was not directly related to an obvious disturbance in any of the parameters examined.

A method is described for the demonstration and enumeration in situ of antigenically related cellulolytic bacteria in the intestinal contents of some herbivores and ruminants, by means of a fluorescent antibody staining technique.

Taxonomy is divisible into three parts: (1) classification, (2) nomenclature, (3) identification. There are rules of nomenclature but none for classification or identification. Six principles are postulated for classification of bacteria and three ways of making identifications are discussed. Both classification and identification depend on characterization of the bacterium, but each makes different use of the individual feature. In classification equal weight is given to each independent character; in identification characters are weighted, some as important (distinguishing), others less so. Exception is taken to the retroactive application of the rules of nomenclature, and the unrealistic starting date (1753) of bacterial nomenclature is criticized. Names act merely as labels and it is suggested that a sequential code should be used, not only as a substitute for a name, but as a means of conveying information about the characters of the organism.