Decline Phase Of Growth Research Articles

Appearance of Mouse-Lethal Toxin in Liquid Cultures of Bordetella pertussis

The mouse-lethal toxin present in liquid cultures of most smooth strains of Bordetella pertussis is known to originate in the cytoplasm of the organism but to be most lethal for mice when released into the supernatant fluid. It is also recognized that cell degeneration and lysis occur in liquid cultures during the stationary and decline phases of growth. For these reasons, it is generally believed that most of the toxicity demonstrable in liquid cultures at the time of harvest is released during the later stages of cultivation, when high alkalinity and aging of cells favor lysis. However, the results reported here have indicated that high levels of mouse-lethal toxicity arise during very early log phase and that the peak of toxicity is reached before the end of the log phase. No further increase in toxicity was observed during stationary and decline phases. The very early appearance of toxicity could not be explained by the presence in the inoculum of a proportion of dead and degenerating cells, and it is concluded that the toxin is produced mainly by actively growing cells. This was confirmed by tests on organisms growing in continuous culture. Electron-microscopic examination of cells from a very early log-phase culture revealed the presence of large numbers of small vesicles on the cell walls of about 5% of the population. It is suggested that these vesicles may be associated with the releases of toxin from living cells. It is concluded that no useful reduction in the toxicity of cultures would result from harvesting before the end of the log phase of growth.

Growth phases of Mycoplasma in liquid media observed with phase-contrast microscope.

Razin, Shmuel (University of Connecticut, Storrs), and Benjamin J. Cosenza. Growth phases of Mycoplasma in liquid media observed with phase-contrast microscope. J. Bacteriol. 91:858-869. 1966-Growth of 11 Mycoplasma strains in liquid media was followed by phase-contrast microscopy. A similar pattern of development was common to all strains. Branching filaments, 0.3 to 0.4 mu thick, characterized the early logarithmic phase of growth. The length of the filaments varied according to the strain tested and the growth medium. Addition of oleic acid to the medium induced the formation of very long filaments by M. laidlawii strain B. Upon aging, the filaments were found to break up into chains of coccoid elements. These chains further fragmented to yield shorter chains and single coccoid elements, which characterized the stationary and decline phases of growth. The size of the coccoid elements increased from 0.3 to 0.4 mu, when formed in the filaments, to 0.6 to 0.8 mu after being released from the chains. Further increase in the size of the cells took place at the decline phase of growth, leading to the formation of very large cells reaching a diameter of 10 to 20 mu. However, these large cells had the appearance of empty vesicles and were apparently nonviable as indicated by viable-count experiments.

EARLY CHROMOSOMAL CHANGES IN SV40-INFECTED HUMAN FIBROBLAST CULTURES.

The relationship between growth-rate changes and chromosomal changes during serial passage of adult human fibroblasts was examined. The phase of rapid growth <i>in vitro</i> is followed by a phase of progressively declining growth rate and finally, by a phase of cellular degeneration. The declining growth phase is associated with a rising level of tetraploid metaphases. In the degenerating phase, the tetraploid level increases further and aneuploid cells first appear. SV<sub>40</sub>-infection of cultured fibroblasts in the declining growth phase results in rapid and extensive chromosome alterations in the first few days following infection. Chromosome alterations in cultures 1 to 7 days after infection were examined in detail. There is a sharp increase in tetraploid metaphases due, in part, to endoreduplication. An increased frequency of breaks was seen within 2 days, and dicentric chromosomes were common by the 4th day. The normally occurring secondary constrictions became more pronounced and a member of the 6-X group, thought to be the late-replicating X chromosome, appeared to be preferentially lost. Telomeric associations involving most members of the complement were frequently encountered; evidence is presented indicating that these associations can lead to the formation of dicentric chromosomes. The telomeres of the long arm of chromosome 4 (or 5) in this cell strain were most often involved in dicentric formation. The rapid response of the several areas of relatively inert chromatin suggests an early viral effect on this material. The relationship, if any, between these early chromosome changes and the changes in the physiology of viral transformed cells remains to be elucidated.

CYCLIC CHEMICAL AND MORPHOLOGICAL CHANGES IN NOCARDIA RUBRA

The morphological growth cycle of Nocardia rubra was related to cellular composition when the organism was grown in a biphasic system for varying lengths of time up to 96hr. The DNA, RNA, lipid, protein, and ash content were determined. The morphology of the organism progressed from long branched filaments in the lag phase of the growth curve to shorter and shorter filaments with decreasing branching during the logarithmic phase. In the stationary phase the N. rubra cells were bacillary, and gradually became coccoid in the declining or death phase.The DNA percentage of the dry cell weight increased during the logarithmic growth phase from 2.2% to 3.0%, and then decreased to 1.5% during the stationary and declining phase. The RNA content was at a maximum of 20.1% in the middle of the logarithmic phase, declined sharply to 10% at the end of this phase, and then decreased more slowly to 4.0% in the declining phase. The lipid content increased rapidly from 9.9% to 20% in the early logarithmic period, at which point it leveled off and increased more gradually to 30.8% in the declining phase. The protein percentage of dry cell weight decreased from 50% to 43% during the early logarithmic period and remained steady throughout the remainder of the logarithmic and stationary phases, and finally decreased in the declining growth phase to 31%. The ash content increased steadily from 8.2% to 9.5% during the incubation period.