The Biphasic or Soil-Water Culture Method for Growing Algae and Flagellata

Abstract

Progress in microbiology, as a result of the adoption of pure-culture methods, has been so striking that in the opinion of some biologists a culture not free of bacteria is not a real culture at all. The statement that bacteria-containing cultures of various kinds may be of use, and the enumeration of successive stages in the attempt to obtain pure cultures (Pringsheim, 1926, p. 287), has, for this reason, led to misunderstandings. To-day, after many more years of research in this field, I can emphasize that uni-algal cultures containing a certain amQunt of bacteria are in more than one respect a suitable basis for investigationi. They are often not merely a preliminary to the production of pure cultures but, if based on ecological considerations, they may also be the best approach to the biology of a form. The matter in question is therefore of more than technical importance. Without cultures originating from single cells, progress along diverse lines would be arrested, and the elucidation of many problems of algal physiology, taxonomy and ecology would take place far more slowly than would be possible with the help of the method described in these pages. One often meets with a few algal cells or filaments which are of special interest but cannot be identified for one or more of the following reasons: scanty representation, absence of reproductive stages, quick movement, the necessity of performing microchemical tests, of applying stains or utilizing special optical equipment. Such obstacles to detailed investigation may be encountered every time they are observed. It may be argued that forms which are only represented by a few individuals are unimportant, but such scarcity may be misleading. The individuals may be concentrated round a particular spot, e.g. a decaying worm, within the habitat. If a certain quantity of water and mud is gathered, the forms inhabiting ecologically different micro-habitats become mingled with one another. In fact biological investigations have often hitherto been restricted to species occurring in relatively dense communities, a condition which may never be realized in nature in the case of various species. This was so with the Astasiaceae, most species of which remained unrecognized until single-celled putrefaction cultures were prepared (Pringsheim,