228 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



An apparent case of algal antagonism, similar 

 to that observed by Pratt, was reported by J. 

 Storey (Worthington 1943), who found that the 

 water of Lake Windermere, when an AsterioneUa 

 bloom is disappearing, is unsuitable for the 

 preparation of culture medium for AsterioneUa. 

 This suggests the possibility that AsterioneUa 

 produces a substance similar to chlorellin pro- 

 duced by Chlorella. Experiments also showed 

 that Skeletonevw produces a substance which in- 

 hibits its further growth (Levring 1945). 



Eodhe (1948) has conducted experiments on 

 the effects of growing two species of planktonic 

 algae in a common medium. He found that 

 AsterioneUa formosa cultured in the presence of 

 Chlorella had a lower rate of division than when 

 grown alone, but a detailed study of the interac- 

 tion was not made. Since completion of the pres- 

 ent investigation the author has learned of the 

 work of Lefevre, Nisbet, and Jakob ( 1949) . These 

 investigators reported inhibition in the growth of 

 some species of algae by "algastatic" substances 

 secreted into the medium by other species of algae. 

 They tested the growth of several species of 

 algae in culture medium prepared with filtered 

 medium in which Scenedesnws had previously 

 grown and in other culture medium prepared with 

 medium in which Pandarina had previously 

 grown. Most of those species tested in these 

 media grew at a slower rate and later the cells 

 of some shrank and died. 



The purpose of the present study was to ascer- 

 tain whether the biological products of a species 

 could influence its own growth as well as the 

 growth of another species under conditions which 

 could be tested in laboratory cultures, and to con- 

 sider whether these materials actually do exert 

 an effect under natural conditions. 



PREPARATION OF CULTURES 



Two species of fresh-water algae, Chlorella 

 ■vulgaris, class Chlorophyceae, and Nitzschia 

 frustulum, class Bacillarieae, were used in these 

 experiments. The author is grateful to Dr. W. T. 

 Edmondson for a subculture of Chlorella and 

 to Dr. Ruth Patrick for identifying the Nitzschia. 

 Also the author appreciates the assistance of Dr. 

 E. G. Pringsheim in isolating the Nitzschia into 

 pure culture. Nitzschia frustidum was originally 

 isolated by the author from a mixture of algae 



obtained from the Carolina Biological Supply 

 Company. This is the first record that this species 

 of Nitzschia has been isolated and cultured in the 

 laboratory. 



LIQUID CULTURE MEDIUM 



These experiments required that both Nitzschia 

 and Chlorella grow well in the same culture 

 medium, thus increasing the difficulty of finding 

 a suitable medium. Many of the better -known 

 culture media were tried but were found to be 

 unsatisfactory for the growth of one or the other 

 of these algae. The author, therefore, devised a 

 nutrient culture medium which proved to be 

 satisfactory for the growth of both Nitzschia and 

 Chlorella. 



Only Pyrex glassware was used and it was 

 cleaned with a mixture of sulfuric acid and 

 potassium dichromate, followed by a thorough 

 rinsing first in tap water and then in distilled 

 water. The culture medium was always auto- 

 claved at least 1 day prior to the time it was to 

 be used, since many investigators have stated that 

 the growth of algae is inhibited if autoclaved 

 medium is used sooner. The formula for this 

 medium which will be referred to as standard 

 culture medium is as follows: 



Ca(N0 3 )4H : 0.04 gram 



MgSO,-7H 2 .02 gram 



KC1 .04 gram 



Na.SiOs  025 gram 



FeCU . 001 gram 



KH 2 P0 4 10 MgAP 



"A-Z" solution 1 cubic centi- 

 meter 

 Double-distilled HsO 1, 000 cubic centi- 

 meters 



An "A-Z" minor nutrient solution, containing 

 small quantities of a number of elements thought 

 to be necessary for plants, has been suggested by 

 Hoagland and Snyder (1933). This solution, 

 modified by omitting the CuS0 4 -5 H 2 and Ti0 2 , 

 was added to the standard culture medium. 



STERILITY 



These experiments were conducted on bacteria- 

 free cultures, as tested from time to time by streaks 

 made on nutrient agar containing 2 percent glu- 

 cose and y 2 percent peptone. Chlorella was main- 

 tained in a pure state by culturing it on agar 

 slants prepared with Detmer's (diluted to two- 

 thirds its normal strength) and Bristol's solutions, 



