Secondary Colonies of Bacteria with Special Reference to Bacillus mycoides

Abstract

20 strains of B. mycoides were studied with reference to the factors involved in the phase of growth resulting in formation of secondary colonies. The secondary phase is due to depletion of preferred nutrients and subsequent utilization of unused substances by certain cells. Ability to attack unused nutrients is acquired through variation due to the specific stimulus exerted by the substance concerned. The substances found suitable for promoting secondary growth were sucrose and protein fractions of unknown identity in digested meat, casein, or gelatin. The strains may be divided into 3 groups on the basis of variation. Group I varies in response to sucrose, but not protein; II, to protein, but not sucrose; III, to both. The sub-races established from secondary colonies show enhanced capacity for utilization of the compound to which variation occurred and do not again produce secondary colonies in its presence. The variants are relatively stable. Variation does not involve other characteristics, such as form of colony, and shape, size or structure of cells. There is no evidence that the secondary colonies in this sp. are due to methods of reproduction other than fission, or that they represent a special phase of complex pleomorphic life history through which the organism must pass in a cyclogenic method of development.