THE ISOLATION, PURIFICATION, AND CULTURE OF BLUE–GREEN ALGAE

ALTHOUGH SPECIES of blue-green algae produce serious nuisance blooms and growths in lakes and streams, surprisingly little work has been done on their nutrition and physiology under controlled conditions in the laboratory. This is undoubtedly due to the difficulties that have been encountered in growing many species of Myxophyceae in pure culture, a point stressed in a recent publication by Rodhe (1948). He was unable, in spite of numerous attempts and modifications of the nutrient medium, to grow such common bloom-producers as Anabaena flos-aquae, Aphanizomenon flos-aquae, Coelosphaerium Naegelianum, or Microcystis aeruginosa in a nutrient solution which was suitable for continuous growth of forty species belonging to Chlorococcales, Volvocales, Conjugatae, Heterokontae, and diatoms. It is true that several species from the family Nostocaceae have been cultured in the laboratory in studies on nitrogen fixation (Allison and Morris, 1930; Allison et al., 1937; Fogg, 1947). However, usually the species grown have not been those that are troublesome in lakes and streams, and, as a result, this work has not contributed specific data on the growth requirements of the bloom producing algae. For this reason, a project was started in this laboratory in 1947, as one part of a general program of Lakes and Streams Investigations at the University of Wisconsin, with the purpose of obtaining basic data on the nutrition and physiology of blue-green algae. It was considered essential to isolate a number of species in bacteria-free cultures before nutrition experiments were started, for only in this way would the data obtained be specific for the algae. This paper is a report on the procedures used and progress made in isolating, purifying from bacteria, and culturing representative species of these organisms. The results of nutritional and physiological studies will be presented in later publications. NUTRIENT SOLUTION FOR BLUE-GREEN ALGAE.-A survey of the literature indicated that nutrient solutions had not been developed which were generally successful for the continuous culture of blue-green algae. Consequently, several solutions were tried which have been used extensively by 1Received for publication August 8, 1949. The authors wish to thank Dr. Francis Drouet of the Chicago Natural History Museum and Dr. R. I. Evans of the University of Wisconsin Botany Department for aid in identification of the blue-green algae isolated in this study. Appreciation is also expressed to Drs. A. Hasler and P. J. Allen for their interest and valuable suggestions, to Dr. J. F. Stauffer for aid, and use of ultraviolet irradiation apparatus, and to Dr. W. B. Sarles and Mr. A. C. Zagallo of the Agricultural Bacteriology Department for final tests of the purity of the irradiated cultures. This work was supported in part by the University Research Committee on funds from the Wisconsin Alumni Research Foundation, from Thomas E. Brittingham, Jr., and from the Lake Mendota Association. other investigators for green algae and diatoms. Of these, Chu No. 10, one of the seventeen nutrient solutions published by S. P. Chu (1942), gave most promising results. It soon was found that Chu No. 10 solution was improved as a culture medium for blue-green algae by substituting an organic source of iron, ferric citrate, for the ferric chloride specified by Chu. This improvement, due to increased iron availability, also has been reported by Rodhe (1948). Furthermore, he found by tests with o-phenanthroline that the addition of an equal amount of citric acid with the ferric citrate stabilized the concentration of reactive iron in the nutrient solution. This modification has been adopted. In the work to be reported here, therefore, the culture solution has the following composition: