ARTIFICIAL MEDIA FOR FRESH-WATER ALGAE: 

 PROBLEMS AND SUGGESTIONS^ 



L. Provasoli and I.J. Pintner 

 Haskins Laboratories 



Fresh-water algae seemingly are ubiquitous: 

 as knowledge Increases the same species are re- 

 corded from all continents. Because most fresh- 

 water habitats are ephemeral, most species survive 

 only if they can form stages resistant to desslca- 

 tlon (Evans, 1958). Overcoming this ecological 

 disadvantage permits species to be transported by 

 high winds and birds all over the globe as constant 

 inocula In search of opportune environments . 



It is also well known that fresh-waters, un- 

 like the almost homogeneous marine environment, 

 display a wealth of environments and algal flora. 

 The distribution of algal species in fresh-waters 

 depends on one hand on the selective action of the 

 chemlco-physical environment and, on the other, 

 on the organism's ability to colonize a particular 

 environment and to compete with the other species 

 living in the same ecological niche . The ecolo- 

 gist and the sanitation scientist seeking a rapid 

 way to distinguish various environments rely more 

 and more on biological markers, the indicator spe - 

 cies which typify each environment more subtly and 

 precisely than can laborious chemical analysis. 



This knowledge is being extended and refined 

 continuously. Meanwhile the ecologist would like 

 to know more precisely the physico-chemical char- 

 acters and boundaries of the ecological niches . A 

 frontal chemical attack is difficult at present be- 

 cause many organic and Inorganic substances are 

 biologically effective and present in waters in ex- 

 treme dilution. Another way to define the chemical 

 environment Is to study the nutritional needs of the 

 indicator species . These, because of their re- 

 stricted occurrence and narrow fit to their environ- 

 ments, are, presumably, outstandingly exacting for 

 at least some Important parameters (stenobionts) . 

 Few, if any, of these species have been cultured 

 aseptlcally, the only way to determine their nu- 

 tritional requirements . Ridding the algae of the 

 unwanted microbial flora, though often tedious and 

 delicate, is only occasionally the main obstacle. 

 Agar-plating, washing and dilution techniques com- 

 bined with the use of antibiotics are well-estab- 

 lished methods [Pringshelm (1946); Provasoli 

 etal., (1951), Lewln (1959), Provasoli and Holz 

 (In press)] . The main difficulty is to design media 

 which will support the aseptic growth of algae 

 whose nutritional requirements are still unknown. 

 A practical approach, when the indicator species of 

 a specialized environment do not grow In present 



media, is to study the nutrition of a species of the 

 same environment which can also live in closely re- 

 lated environments . An analysis of their nutritional 

 requirements may show how to construct media ade- 

 quate for the indicator species . Selection and con- 

 struction of media would perhaps be facilitated if 

 one had: a) data on the relative Importance of the 

 chemical components of the waters , b) data on the 

 nutritional requirements of the different groups of 

 algae, c) some guideposts in solving some of the 

 problems of designing artificial media. 



Relative Importance of the Chemical Factors 

 of the Environment 



In dealing with organisms of unknown nutri- 

 tional requirements one can obviously benefit 

 greatly in mimicking as closely as possible the 

 chemical environment . 



Due to the diverse composition of fresh- 

 waters one should know the following parameters in 

 order of Importance: a) total solids, b) the prevail- 

 ing major ions, c) pH, d) main trace metals, e) ra- 

 tios of monovalent/divalent cations and of Ca/Mg, 

 and_f) content of organic matter (which may act as 

 trace metal solubllizers or as growth factors) . 



The pertinence of these considerations is em- 

 phasized by Rodhe's success (1948) in studying in 

 detail the mineral requirements of Anklstrodesmus 

 falcatus . At the end of his studies he compounded 

 a medium in which all the major minerals were 

 added at optimal concentration. This medium is 

 very close to the composition of the waters of Lake 

 Erken, where Anklstrodesmus blooms, and the aver- 

 age composition of the waters of many Swedish 

 lakes. This medium proved to be satisfactori' for 

 most of the algal species Inhabiting Lake Ekren and 

 would probably sustain some growth of all the spe- 

 cies when enriched with vitamins (at the time it 

 was not known that many algal species require vit- 

 amins) . 



The medium of Rodhe might have been quite 

 different had he chosen to study an eurybiont and 

 not a stenoblont. The eurybiont, depending upon 

 the species selected, would have led to construct 

 several media specific for the species in question, 

 and therefore very different from the natural waters . 



The most important parameter, especially for 

 oligotrophic algae, seems to be the total-solids 



■^ Aided in part by research grant G-3216 from National Institutes of Health. 



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