The Ultrastructure of S and R Variants of Brucella abortus Grown on a Lifeless Medium

Abstract

SUMMARYAn electron microscopic investigation was carried out on thin sections of both S and R variants of Brucella abortus, strain S A : no ultrastructural differences were noted between the two variants.The cells are limited by a cell wall, comprising an outer triple-layered membrane (65-80 8. thick) and an inner homogeneous layer of variable thickness, and a triple-layered cytoplasmic membrane about 70 A. thick.The cytoplasm and nucleoplasm of brucellae are similar to those of other bacteria. A characteristic feature of these organisms is the presence of membranous structures (300-800 A. in diameter) associated with the cytoplasmic membrane. These 'peripheral formations ', which occur singly or in clusters, do not appear to arise by obvious invagination of the cytoplasmic membrane. No evidence has been obtained for the existence of capsules in virulent brucellae. INTROIIUC'l'IOISThe aim of the present investigation was to study the ultrastructure of Brucella abortus grown either on a lifeless medium or within monocytes maintained in vitro. To our knowledge no detailed study of this organism, employing present-day techniques of electron microscopy, has been published to date.The first paper in this series deals with the morphology of S and R variants of BruceEEa abortus strain S A , grown on a lifeless medium. Our interest in comparing both variants stemmed from the notion that the mutational event occurring in B. abortus, which results in a change of genotype from S to non S (e.g. R or M), is associated with a variety of phenotypic changes. These include loss of or decrease in virulence, loss of the ability to multiply intracellularly (Braun, Pomales-Ldbron & Stinebring, 1958), change in colonial morphology from smooth to non-smooth (e.g. rough or mucoid), change in surface properties resulting in agglutination, change from sensitivity to resistance to brucella phage (Stinebring & Braun, 1959), and changes in antigenic composition. These alterations, and particularly the last four, suggested that morphological changes may occur in the surface structure of the bacteria. It seemed interesting therefore to investigate whether the above phenotypic changes would be reflected in ultrastructural differences detectable with the electron microscope.

Localization of Antibodies by Electron Microscopy in Developing Antibody-Producing Cells

“…A more detailed description of the cells present in the lymph nodes of hyperimmunized rabbits will be published elsewhere (11).…”

“…FT molecules, invisible with the electron microscope, cannot however be excluded. Unlike blasts and plasma cells, the reticular cells and macrophages of our preparations often contained relatively large amounts of FT, either enclosed within vacuoles or free in the cytoplasm (11,37). All the above findings favour the view, supported also by other authors (5, 22,23), that blasts (and hence plasma cells) are not derived from those cells which have taken up most of the antigen.…”

Fine Structure of Strictly Anaerobic, Non‐Spore‐Forming, Gram‐Negative Bacilli

“…The cell division of gram negative bacteria has been considered to be achieved by the concomitant invagination of the cytoplasmic membrane and the cell wall [9,15,18,24]. In an unusual condition such as in the cultivation at 45 C, the cell division of E. coli or Spirillum screens was found to be similar to that of gram positive.…”

“…of other gram negative bacteria was composed of the cytoplasmic membrane and the septal element which was continuous with the innermost layer of the cell wall [24]. The innermost layer was considered to be mucopeptide layer [9,424]. The P-layer of the cell wall of B. convexus was relatively homogeneous and the dense innermost layer of E. coli and S. serpens [24] was not usually detectable.…”

“…The cell division of gram negative bacteria has been considered to be achieved by the concomitant invagination of both the cytoplasmic membrane and the cell wall [9,15,18,24]. Recently, the formation of mesosomes by infolding of the cytoplasmic membrane at the division plane or the formation of the transverse septum was observed in certain gram negative bacteria [1,2,4,5,7,11,19,20].…”