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Publisher Summary This chapter discusses the influence of cultural conditions on bacterial cytology. There are two mechanisms whereby cultural conditions can alter bacterial morphology. First, phenotypic modifications may be directly impressed; such cases form the main subject of the chapter. The inducing condition modifies the metabolism of all the growing cells in the culture and within a few generations changes their composition and structure. The change is nonheritable, and the acquired character is soon lost when the cells are again grown in the absence of the inducing condition. The second mechanism involves an environmentally conditioned selection of mutant cells with altered morphology. Small numbers of these originate spontaneously in the parent culture, and prolonged or serial cultivation under conditions to which they are better adapted than the parent-type cells enables them to outgrow and replace the latter. This kind of change is heritable. It may be stable and irreversible, but in some cases, a reverse mutation can occur and appropriate cultural conditions may reselect the original form. Bacterial morphology may be directly modified according to the type and balance of nutrients in the culture medium, the pH of the medium, the degree of aeration, the temperature of incubation, the presence of antibacterial agents, the age of the culture, and other factors. |
