Biochemical and cytological observations during the reversing process from spheroplasts to rod-form cells in Escherichia coli

Survival of a psychrophilic marine Vibrio under long-term nutrient starvation

Ant-300, a psychrophilic marine vibrio isolated from the surface water of the Antarctic convergence, was starved for periods of more than 1 year. During the first week of starvation, cell numbers increased from 100 to 800% of the initial number of cells. Fifty percent of the starved cells remained viable for 6 to 7 weeks while a portion of the population remained viable for more than 1 year. During the first 2 days of starvation, the endogenous respiration of the cells decreased over 80%. After 7 days, respiration had been reduced to 0.0071% total carbon respired per hour and remained constant thereafter. After 6 weeks of starvation, 46% of the cellular deoxyribonucleic acid had been degraded. Observation of the cellular deoxyribonucleic acid with Feulgen staining before starvation showed the average number of nuclear bodies per cell varied from 1.44 to 4.02 depending on the age of the culture. A linear relationship was found between the number of nuclear bodies per cell and the increase in cell numbers upon starvation. Our data suggest that Ant-300 is capable of surviving long periods of time with little or no nutrients and is therefore well adapted for the sparse nutrient conditions of the colder portions of the open ocean.

Reversion to bacillary forms of Serratia marcescens spheroplasts induced by carbenicillin. Scanning electron microscopic study

Bacterial cells of Serratia marcescens were easily induced to form spheroplasts in liquid medium by the addition of carbenicillin. The spheroplasts were unable to divide, but they were able to revert to the bacillary forms in liquid medium not containing carbenicillin. Four phases of the reversion sequence could be differentiated by scanning electron microscopy. (1) After 3 hr of incubation in carbenicillin-free medium, some projections arose out of the spheroplasts, and grew and elongated. (2) Their elongation resulted in a morphological change in the spheroplasts from spherical bodies to long irregular bacillary forms. (3) Further incubation caused several constricted areas in the bacillary form. (4) The long bacillary forms split along the constricted areas to become the parent bacillary forms of S. marcescens. When the long bacillary form that developed during the reversion was retreated with carbenicillin, it was immediately induced to become a spheroplast again.

Fusion of bacterial spheroplasts by electric fields

Spheroplasts of Escherichia coli or Salmonella typhimurium were found to fuse in an electric field. We employed the fusion method developed by Zimmermann and Scheurich (1981): Close membrane contact between cells is established by dielectrophoresis (formation of chains of cells by an a.c. field), then membrane fusion is induced by the application of short pulses of direct current. Under optimum conditions the fusion yield was routinely 90%. Fusable spheroplasts were obtained by first growing filamentous bacteria in the presence of cephalexin, then converting these to spheroplasts by the use of lysozyme. The fusion products were viable and regenerated to the regular bacterial form. Fusion of genetically different spheroplasts resulted in strains of bacteria possessing a combination of genetic markers. Fusion could not be achieved with spheroplasts obtained by growing the cells in the presence of penicillin or by using lysozyme on bacteria of usual size.

Characteristics of chromosomal DNA isolated from Escherichia coli spheroplasts

The chromosomal DNA of Escherichia coli spheroplasts induced by penicillin G was studied biochemically and electron microscopically. Although the spheroplasts were unable to divide, they continued to synthesize chromosomal DNA for several hours even in the presence of penicillin G. Some differences were observed between the chromosomal DNA of the parent cells and that of the spheroplasts in sucrose gradient centrifugation and electron microscopy; two types of chromosomal DNA, a slower sedimenting form and a faster sedimenting form, were released from the gently lysed parent cells. The former was membrane-free folded chromosome and the latter was membrane-associated chromosome. In contrast, the chromosome from the spheroplast showed a single intermediate value of sedimentation coefficient between those of the chromosomal DNA from the parent cell. Cytochrome spreading for electron microscopy showed that the spheroplast chromosomal DNA formed an aggregated mass consisting of several chromosome-molecules of the parent cell.

[The development and the reversion of spheroplasts of a diaminopimelic acid-auxotrophic mutant of Escherichia coli]

1. The formation and reversion of spheroplasts of the diaminopimelic acid-auxotrophic mutant Escherichia coli K 12, 335, DAP-, R+TEM in a medium lacking diaminopimelic acid have been investigated by microphotography: During their development from rod form cells to spheroplasts cells on slide-surface-agar preparations underwent two successive cell divisions in the course of which the cells retained their rod form. The cells formed by these divisions partitioned into a varying number of spheroplasts of different size. The reversion of spheroplasts to rod form cells, started by the addition of diaminopimelic acid showed two characteristic steps: Each spheroplast partitioned again into several spheroplast-like cell bodies; most of them reverted directly to rod form cells. 2. The release of the R-factor mediated periplasmic TEM-beta-lactamase, E. C. 3.4.2.6., into the growth medium during the development of spheroplasts attained more than 50% of the entire TEM-beta=lactamase activity. The spheroplasts showed a multiple enhancement of TEM-beta-lactamase activity per mg cell protein compared with rod form cells.

Morphology and round body fermation in Vibrio marinus

The morphology of Vibrio marinus MP-1 was studied by phase and electron microscopy. The ultrastructure of the vibrio form of V. marinus was found to be typically gram-negative with a trilaminar plasma membrane and cell wall. The coccoid or round bodies noted in otherwise pure cultures of V. marinus were frequently found in early and late stationary phase of growth. The round bodies in ultrathin section were found to contain at least one, and often three or four, cell units. Three types of round bodies were observed in ultrathin section, each differing in size and behavior: "spherules," "spheres" or the "round body," and "giant cells" or "macrospheres." The round bodies appeared to be associated with, or to result from, the constrictive cell division of V. marinus.

Properties of rod cells reversed from penicillin spheroplasts in Escherichia coli

Hirokawa, Hideo (The University of Tokyo, Tokyo, Japan). Properties of rod cells reversed from penicillin spheroplasts in Escherichia coli. J. Bacteriol. 91:125-128. 1966.-Spheroplasts of Escherichia coli B-054 were formed by penicillin, and the properties of rod cells reversed from the spheroplasts were examined. It was found that the rod cells were not capable of forming colonies when placed in a minimal medium immediately after the reversion, the postaddition of the nutrient to this medium being without effect. In this respect, the so-called residual cells which did not convert to spheroplasts by penicillin treatment behaved just as the reversed rod cells. These two types of cells, the reversed and residual rod cells, however, could grow up to form colonies when they were cultivated in a complex medium immediately after the reversion. The nutrient requirement and penicillin sensitivity of the progeny of these cells were found to be quite similar to those of the original untreated cells. Accordingly, it was concluded that the nutritional defect induced by penicillin treatment was not a hereditary change.

THE LOCATION OF THE MUCOPEPTIDE IN SECTIONS OF THE CELL WALL OF ESCHERICHIA COLI AND OTHER GRAM-NEGATIVE BACTERIA

Electron micrographs of sections of Escherichia coli have shown that the wall has an extra component 20–30 Å in thickness on the inside of the usual double-track profile. Demonstration was aided by treating the sections with uranium, lanthanum, thallium, or lead salts. This innermost layer alone was lost in spheroplasts produced by penicillin poisoning or treatment with lysozyme-EDTA, and was removed from isolated cell walls by lysozyme. The innermost layer is considered, therefore, to contain the mucopeptide characteristic of bacteria. The inner taut layer (or "intermediate layer") of Spirillum serpens, Vitreoscilla sp., and Simonsiella sp. was also found to be lysozyme sensitive. In the latter species this layer was the sole component of the septum, so that the outer cell wall components enclosed the elements of the trichoma. Other components were less easily localized but it was considered that the lipoprotein layer was outside of the limits of the wall profile usually visualized in sections. The outer layers generally loosened during embedding, but in E. coli and some others the layers all stayed tightly adherent to each other. The Gram-negative bacteria seem to have the double-track layer and the mucopeptide as a basic complement for the cell wall.