Sulphur bacteria : a monograph / by David Ellis.

  • David Ellis
Date:
1932
Catalogue details

Licence: In copyright

Credit: Sulphur bacteria : a monograph / by David Ellis. Source: Wellcome Collection.

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    Pleomorphism. By pleomorphism is meant the capacity of an organism to assume diverse forms. A culture of bacteria may contain several variant forms simultaneously, or these may be formed in succession. Bacteria in general are noteworthy for the ease with which changes in form occur in them. The ease with which certain physiological changes bring about changes in the external appearance of bacterial cells is a matter of common knowledge. Probably no other organisms possess greater plasticity in this respect. Unless, for example, a wide range is given to the dimensions of a bacillus, a state- ment of its length or its thickness has little value for purposes of identification. It is a matter of common ob- servation, too, that, under certain circumstances the rate of growth in size and the rate of division of bacteria do not run parallel. The rate of each is dependent on circumstances of which at present we have very little knowledge. If the rate of division is accelerated the individuals of successive generations become progressively smaller. Under certain cir- cumstances the rate of division of Crenothrix polyspora, one of the iron bacteria, may so far exceed the rate of its growth that the individuals may be so reduced in size that they are barely visible with the highest powers of the microscope. Again, the change that takes place in the size of the individuals of a bacterial culture after frequent subculture is well known. Further, every living bacterial cell is at all times covered by a delicate covering of slime formed by transformation of the outermost layer of the membrane. Given certain conditions, this slime formation increases in intensity, and the motility of the cell is retarded, and may even cease altogether. Conversely, by the elimination of excessive slime formation non-motile forms may be made to assume motility.* Other instances could be adduced in illustration of the morphological plas- ticity of bacteria. Over 2000 species of the genus bacillus * By subculturing at the very earliest sign of growth on the surface of agar-slope cultures, the motility of organisms may be considerably en- hanced, and even forms regarded as non-motile may be made to assume motility (Ellis (2-3)).