R. Y. Stanier

The Concept of a Bacterium

Since the earliest days of microbiology, the biological nature and relationships of the bacteria have been subjects of perennial discussion. Why have these questions obsessed some members of each succeeding generation of microbiologists ? There can be no doubt about the principal reason. Any good biologist finds it intellectually distressing to devote his life to the study of a group that cannot be readily and satisfactorily defined in biological terms; and the abiding intellectual scandal of bacteriology has been the absence of a clear concept of a bacterium. Our first joint attempt to deal with this problem was made 20 years ago (STANIER and VAN NIEL 1941). At that time, our answer was framed in an elaborate taxonomic proposal, which neither of us cares any longer to defend. But even though we have become sceptical about the value of developing formal taxonomic systems for bacteria (see VAnNIEL 1946, for an exposition of the reasons), the problem of defining these organisms as a group in terms of their biological organization is clearly still of great importance, and remains to be solved. A great deal of relevant information has emerged in recent years, and the time therefore seems opportune for a fresh analysis of this question. I t is not our intention to review here the development of ideas about the nature and relationships of the bacteria ; readers who are interested in the historical aspects of the problem can find authoritative and very full accounts in PRINeSI~EI~ (1923, i949) and VAN NIEL (1955).

Studies on the macromolecular organization of microbial cells

Five different methods of preparing extracts from bacterial cells yielded similar distributions of macromolecular constituents as indicated by ultracentrifugal patterns. Extracts from a number of different bacteria showed essentially similar patterns. Three principal components were found, with sedimentation constants of approximately 40, 29, and 5 S. In many extracts, it was evident that the most slowly moving peak consisted of two components, a broad diffuse boundary and a sharp spike containing desoxypentose nucleic acid. Extracts from the photosynthetic bacterium Rhodospirillum rubrum contained, in addition to the above-mentioned components, a component of very large size (sedimentation constant approximately 190 S), with which the entire pigment complement of the cells was associated. Chemical analyses of crudely fractionated extracts showed that the bulk of the pentose nucleic acid of the cells was associated with the particles of sedimentation constants from 20 to 40 S, while the desoxypentose nucleic acid was almost all present in the fraction of lower sedimentation rate.

Fatty acid composition and physiological properties of some filamentous blue-green algae

SummaryThe fatty acids of 32 axenic strains of filamentous blue-green algae have been analyzed. As an aid to the interpretation of the results, the strains have been assigned to provisional typological groups based upon their morphology and certain physiological characters. The latter are the ability to grow heterotrophically in the dark with glucose as carbon and energy source, the ability to grow in the light at the expense of glucose in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and the ability to synthesize nitrogenase under anaerobic conditions in the light. Each typological group has been given an appropriate generic name.The strains examined for fatty acid composition can be divided into groups according to the major fatty acid of highest degree of unsaturation found in each strain as was done for the unicellular strains examined previously in this laboratory. Four metabolic groups of strains of unicellular and filamentous blue-green algae can be recognized: 1. those in which there is little or no desaturation of oleate; 2. those in which linoleate is desaturated toward the ω-end of the molecule to give α-linolenate; 3. those in which linoleate is desaturated toward the carboxyl end of the molecule to give γ-linolenate; 4. those in which octadecatetraenoate is synthesized. The nature of the major cellular fatty acids of two of the strains examined is the same whether growth is in the light or in the dark on glucose. All filamentous strains contain glycolipids with the properties of mono- and digalactosyldiglycerides.

The chlorophylls of green bacteria

Contrary to previous assumptions, at least two different molecular species of chlorophyll exist among the green bacteria. Two strains of Chlorobium thiosulfatophilum each contain a single, distinct type of chlorophyll. The spectral properties of these two pigments and of the correponding pheophytins are described, together with certain of their chemical properties.

Metabolism of glucose by unicellular blue-green algae

SummaryA facultative photo- and chemoheterotroph, the unicellular bluegreen alga Aphanocapsa 6714, dissimilates glucose with formation of CO2 as the only major product. A substantial fraction of the glucose consumed is assimilated and stored as polyglucose (probably glycogen). The oxidation of glucose proceeds through the pentose phosphate pathway. The first enzyme of this pathway, glucose-6-phosphate dehydrogenase, is partly inducible. In addition, the rate of glucose oxidation is controlled, at the level of glucose-6-phosphate dehydrogenase function, by the intracellular level of an intermediate of the Calvin cycle, ribulose-1,5-diphosphate, which is a specific allosteric inhibitor of this enzyme. As a consequence, the rate of glucose oxidation is greatly reduced by illumination, an effect reversed by the presence of DCMU, an inhibitor of photosystem II.Two obligate photoautotrophs, Synechococcus 6301 and Aphanocapsa 6308, produce CO2 from glucose at extremely low rates, although their levels of pentose pathway enzymes and of hexokinase are similar to those in Aphanocapsa 6714. Failure to grow with glucose appears to reflect the absence of an effective glucose permease. A general hypothesis concerning the primary pathways of carbon metabolism in blue-green algae is presented.

The path of carotenoid synthesis in a photosynthetic bacterium

Abstract Exponentially growing cells of the photosynthetic bacterium Rhodospirillum rubrum contain a mixture of carotenoids: lycopene, P481, spirilloxanthin, and their monohydroxy derivatives. When such cells are resuspended in buffer and incubated anaerobically in the light, the total amount of carotenoid pigment in the cells remains constant, but there is a net synthesis of spirilloxanthin at the expense of the other carotenoids originally present. This synthesis proceeds from lycopene through P481. Added to a photosynthetically growing culture of R. rubrum at a final concentration of 7 · 10 −5 M , diphenylamine causes a complete arrest of normal carotenoid synthesis, accompanied by a rapid accumulation of carotenoids more saturated than lycopene. Phytoene, phytofluene, hydroxyphytofluene, ζ-carotene, hydroxy-ζ-carotene, neurosporene and hydroxyneurosporene are the principal accumulating compounds. If the diphenylamine is removed and the cells are resuspended in buffer and incubated anaerobically in the light, an endogenous synthesis of normal carotenoids takes place at the expense of all the accumulated precursors with the probable exception of phytoene. The kinetic analysis of this endogenous synthesis reveals the sequential relationships between the participating carotenoids.

The metabolism of aromatic acids by Pseudomonas testosteroni and P. acidovorans

SummaryP. testosteroni oxidizes benzoate, m-hydroxybenzoate and p-hydroxybenzoate to protocatechuate, which is dissimilated through the meta cleavage pathway. P. acidovorans uses the same pathway for the oxidation of p-hydroxybenzoate. but employs the gentisate pathway for the oxidation of m-hydroxybenzoate. The difference between the two species with respect to m-hydroxybenzoate metabolism reflects a difference with respect to the specificity of their m-hydroxybenzoate hydroxylases: the enzyme of P. testosteroni hydroxylates in the 4 position, and that of P. acidovorans in the 6 position.

Further mutational changes in the photosynthetic pigment system of Rhodopseudomonas spheroides.

SUMMARY: Some 50 mutants, which differ from the wild type in the nature of their pigment systems, were isolated from the non-sulphur purple bacterium, Rhodo-pseudomonas spheroides. They fall into five main groups. The group of colourless mutants is incapable of photosynthetic growth, and devoid both of chlorophyll and carotenoids. The remaining groups still contain bacteriochlorophyll, but differ chemically from the wild type and from one another in their carotenoid pigments; all are capable of photosynthetic growth. The wild type contains two principal carotenoids, one red and one yellow. The dark red mutants contain both wild-type carotenoids and traces of a new red carotenoid. The brown mutants contain approximately equal amounts of the wild-type yellow carotenoid and of neurosporene, together with traces of the wild-type red carotenoid. The green mutants contain neurosporene and a dihydroxy derivative, but neither of the wild-type pigments. The blue-green mutants contain phytoene, a colourless polyene, but are completely devoid of coloured carotenoids. The infra-red spectrum of cells of the blue-green mutant is markedly different from that of the wild type and of the other photosynthetic mutants, despite the fact that its chlorophyll is chemically identical with theirs.

Taxonomic studies on some cram negative polarly flagellated “hydrogen bacteria” and related species

SummaryThe properties of several named and unnamed strains of polarly flagellated “hydrogen bacteria” are described and compared with those of related autotrophic and non-autotrophic species. Two new species ofPseudomonas are described: one, a yellow-pigmented hydrogen bacterium,P. palleronii Davis; the other, a non-autotrophic, non-pigmented species,P. delafieldii Davis.

Studies on the role of carotenoid pigments in a chemoheterotrophic bacterium, corynebacterium poinsettiae

SummaryThe hypothesis that colored carotenoids can protect chemoheterotrophic microorganisms from damage by visible light has been investigated. Corynebacterium poinsettiae, a bacterium that forms the three carotenoid pigments lycoxanthin, cryptoxanthin and spirilloxanthin, was used as test organism. Non-pigmented cells, in which the normal carotenoids were largely replaced by the colorless C40 polyene, phytoene, were obtained by two methods: isolation of a mutant with a block in carotenoid synthesis; and cultivation of the parent strain in the presence of diphenylamine, a specific chemical inhibitor of carotenoid synthesis.Comparative studies of the effects of visible light on dye-sensitized pigmented and non-pigmented cells showed that non-pigmented cells can be rapidly killed by exposures which are without effect on pigmented cells. Both physiological and genetic suppression of pigment synthesis produce photosensitivity. The non-pigmented mutant is killed by ultraviolet light at the same rate as the pigmented parent strain, indicating that the acquired photosensitivity of the former is specific for visible light.