Survival strategies of bacteria in the natural environment.

Respirometer experiments show that when a dry soil is moistened a characteristic pattern of decomposition occurs in which an initial period of relatively rapid decomposition (Stage 1) falls, during a few days, to a slow steady rate (Stage 2). This pattern is repetitive with successive dryings and rewettings and is common to all soils so far investigated. The magnitude of decomposition depends in the percent carbon in the soil and on the drying conditions, air-drying being less effective than oven-drying. Decomposition during Stage 1 conforms approximately to a first-order reaction and proportionate amounts of nitrogen are mineralised. A similar pattern of decomposition occurs under field conditions throughout successive wet and dry seasons. Evidence is presented to show that decomposition involves direct microbial attack of the solid organic substrate and that the recurrent pattern of decomposition is due to the state in which the microbial population is left after drying and its subsequent behaviour on rewetting. The rapid decline in the rate of decomposition on rewetting (Stage 1) appears not to involve (1) the development of toxic conditions, (b) physical changes in the soil (since similar patterns of decomposition also occur with organic material alone or in sand) or (c) rapid decomposition of organic material made soluble by drying. The operation and repetition of this pattern of decomposition in the field has important consequences in the rundown of soil carbon and the mineralisation of soil nitrogen particularly where well-defined wet and dry seasons occur. These consequences are discussed in relation to climate and certain agricultural practices.

The effect of soil drying on humus decomposition and nitrogen availability

A simple method to detect lipolytic activity of micro-organisms is described. The formation of lipase is demonstrated by adding water-soluble Tweens to a nutrient medium. Around the colonies with lipolytic activity there appears a well visible halo which is due to crystals of the calcium salt of the fatty acid liberated by lipolysis. The three chief advantages of the use of Tweens are that:

1.

there is an optimum contact between the growing cells and the fatty substrate, which is necessary in those cases in which the formation of lipase is adaptive.




2.

they can be used in studies on the specificity of the lipase.




3.

the results are directly visible.

A Simple Method for the Detection of Lipolytic Activity of Micro-Organisms and some Observations on the Influence of the Contact between Cells and Fatty Substrates.

A quantitative assay of candidacidal activity based on differential staining of non-viable Candida albicans by methylene blue was developed and applied to studies of leukocytes from normal individuals and patients with fungal and other infections. Serum factors were necessary for optimal phagocytosis of C. albicans but lacked direct candidacidal activity. Normal human neutrophils (38 studies) killed 29.0 +/- 7.4% of ingested C. albicans in 1 hr. Eosinophils and monocytes killed a smaller percentage. Neutrophil candidacidal activity did not require protein or ribonucleic acid synthesis by the leukocyte but was inhibited by anaerobic conditions, potassium cyanide, and colchicine. Leukocytes of a patient with hereditary myeloperoxidase deficiency and of three children with chronic granulomatous disease phagocytized C. albicans normally, yet failed to kill them. Our data suggest that the neutrophil can play an important role in resistance to Candida infection and that the lysosomal enzyme myeloperoxidase and its oxidant substrate hydrogen peroxide are the major participants in neutrophil candidacidal activity.

Interaction of Candida albicans with human leukocytes and serum.

Defensins are small, multifunctional cationic peptides They typically contain six conserved cysteines whose three intramolecular disulfides stabilize a largely β-sheet structure This review of human α-defensins begins by describing their evolution, including their likely relationship to the Big Defensins of invertebrates, and their kinship to the β-defensin peptides of many if not all vertebrates, and the θ-defensins found in certain non-human primates We provide a short history of the search for leukocyte-derived microbicidal molecules, emphasizing the roles played by luck (good), preconceived notions (mostly bad), and proper timing (essential) The antimicrobial, antiviral, antitoxic, and binding properties of human α-defensins are summarized The structural features of α-defensins are described extensively and their functional contributions are assessed The properties of HD6, an enigmatic Paneth cell α-defensin, are contrasted with those of the four myeloid α-defensins (HNP1-4) and of HD5, the other α-defensin of human Paneth cells The review ends with a decalogue that may assist researchers or students interested in α-defensins and related aspects of neutrophil function

α-Defensins in human innate immunity.

The structure of the bacterial cell has been the subject of numerous investigations since the early years of bacteriology. Up to a quarter of a century ago a considerable literature accumulated, as it is easy to see from the last extensive review, "Die Zelle der Bakterien,"' published by A. Meyer in 1912. Since then the literature has been relatively scanty. It can, therefore, be said that this interesting branch of bacteriology has been sadly neglected in recent years. The writer knows of only one other lecture course in this country, aside from his own, which teaches cytology and morphology of bacteria exclusively. Surprise is often expressed that there should be enough known on the subject to justify a course in cytology and morphology. The following brief review is an outline of the main topics investigated and the progress made.

Cytology of bacteria

The early literature on the cytology of M1ycobacterium tutbercuilosis was reviewe(I by Knaysi (1929). Among the reports not reviewed by him are those of Feinberg (1900), Nakanishi (1901), 'Minder (1916), Kirchensteins (1922), and Petit (1926). Feinberg observed a red nucleus and a bluie cytoplasm in cells stainedl by a modified Romanowski's soluition. iNakanishi demonstrated by postvital staining wi-ith methylene blute a round body locatedl near the middle of the cell; sometimes there was a constricted body or there were two round bodies. 'Minder distinguished between MIuch's granules and polar bodies, although the latter w-ere demonstrable by Mluch's method of staining. He stated that the grantules w-ere neither spores nor decomposition products. Kirchensteins, using a complicated method of staining with basic fuchsin, concluded that a nuclear apparattus existed consisting of several granules united by fine filaments. Petit did not attribute to the granules a nuclear nature. Knaysi (1929) studiedI a strain, originally of the human type, which had lost its pathogenicity; his observations were summarized as follows:

The cytology of an avian strain of Mycobacterium tuberculosis studied with the electron and light microscopes.

Observations on the Cell Division of Some Yeasts and Bacteria.

https://mmbr.asm.org/content/mmbr/12/1/19.full.pdf

The endospore of bacteria.

In the early application of the electron microscope to the examination of bacteria, the method of preparation involved the preparation of a distilled water suspension of the organisms and the evaporation of a drop of the suspension on a suitable supporting membrane. Although it was recognized that such treatment probably gave rise to considerable artifacts, this procedure nevertheless was used in most of the published work (Mudd and Anderson, 1944). Recently some of the artifacts introduced by this method of preparation have been investigated and a new method has been suggested (Hillier and Baker, 1946; Edwards and Wyckoff, 1947). This method involves the intact removal of the surface layer of organisms from a culture of a solid medium by means of a thin plastic membrane formed in place on the culture by the evaporation of a suitable solution. Further work on this technique has shown that although it is ideal for the examination of very young cultures of certain strains of organisms, it has numerous serious limitations that will prevent it from being generally useful. For instance, even for those types of organisms for which it can be used, it is not successful if the growing conditions are not \"quite right.\" More serious, however, is that the physical organization of the culture is maintained only in the outermost surface of the growth. Thus, unless the preparations use single-layer growths of strong cells, the resulting specimen is confused by material pulled from inner layers in disorganized masses. This last difficulty was particularly troublesome in recent attempts by one of us to follow, by this technique, the infection of Escherichia coli by T2 bacteriophage. As a result of these difficulties a new technique has been developed that appears to have many advantages. Basically, it involves growing the organisms directly on the thin supporting membrane of the electron microscope specimen mount in such a way that any directcontact with theorganism is avoidedthroughout the procedure. The only disturbance of the organisms that can introduce artifacts is a final desiccation. For organisms grown on ordinary media, such artifacts have not been observed. At the time of writing, this technique has proved unifornly successful in the preparation of specimens of Bacillus mycoides, Bacillus megatherium, and Escherichia coli grown under a number of different conditions and subsequently treated in several different ways. It would appear in principle at least that the technique should be successful for all organisms that produce surface colonies.

Georges Knaysi

Papers

Cytology of bacteria

The cytology of an avian strain of Mycobacterium tuberculosis studied with the electron and light microscopes.

Observations on the Cell Division of Some Yeasts and Bacteria.

The endospore of bacteria.

New Preparation Techniques for the Electron Microscopy of Bacteria.