Bacterial Variation: An Inquiry into the Underlying Principles Governing the Cell Morphology of Bacillus megatherium

Abstract

The formation and further development of individual Bac. megatherium cells (both variant forms and "normal" rods) growing in microcultures on hanging blocks of plain extract agar (30[degree]C) were studied. Changes in cellular morphology were followed under a 1/12 inch oil immersion objective, using 12 X and 20 X compensating eye pieces. Repeated camera lucida drawings were made. The cell morphology of Bac. megatherium appeared to be governed largely by environmental conditions. Slight changes in environment were responsible for striking changes in cell form. Cellular variation could be related directly to the degree of growth crowding and, consequently, to changes which took place in the medium as a result of metabolic activity. The factors which stimulated cellular variations were unfavorable to continued normal growth, and variation was possible only when favorable and unfavorable conditions were so balanced as to permit slow growth in the face of adverse circumstances. Partial oxygen starvation was, for example, responsible for at least certain types of variation. Some variant cells were apparently better able to resist the unfavorable conditions that resulted in their formation than were "normal" rods, and hence may be regarded as adaptation forms which aid in the preservation of the species, rather than as definite morphological stages in an intricate reproductive cycle. No evidence was obtained which would indicate that definite cellular forms could develop from finely granular and apparently structureless material (so-called symplasm).