THE DISTRIBUTION OF BACTERIA IN LAKES 



By ARTHUR T. HENRICI 



DEPARTMENT OF BACTERIOLOGY AND IMMUNOLOGY, UNIVERSITY OF MINNESOTA 



MINNEAPOLIS, MINN. 



Jc mehr der Einblick in das Leben cines Sees 

 vertieft werden soil, desto mehr mlissen audi die 

 Bakterien in den Bereieh der Untersucluing gezog- 

 en werden; ja niau darf sogar bebaupten, dass fiir 

 das Yerstiindnis der oft stark ineinandergreifend- 

 en Lebenszvklen in eineni See, besonders ini eutropli- 

 en See, iiberhaupt fiir den gesamten Stoft'lianslialt 

 in eieneni stehenden GewJisser, die Kenntnis der 

 Tjitigkeit sowolil der im freien Wasser als der im 

 Schlaniuie lebenden Bakterien unerliisslich ist. 



— Huber-Pestalozzi (1938). 



This quotation may well serve to indicate 

 the nature of the problem to be solved in 

 studying" the bacteria of lakes. A similar 

 quotation might be derived from a number 

 of general works on limnology, for most 

 limnologists have realized that bacteria play 

 an important part in the economy of lakes. 

 But definite information upon this phase 

 of lake study is almost completely lacking; 

 for bacteriology has lagged considerably be- 

 hind the other biological sciences in partici- 

 pating- in the study of lake ecology. 

 Whereas botanists and zoologists have long 

 since made their collections and classified 

 their species, and have studied the distri- 

 bution of them, so that they are now able 

 to synthesize the results of their investiga- 

 tions from the standpoint of lake-types, etc., 

 bacteriologists have yet to learn, for the 

 most part, Avhat species of bacteria live 

 characteristically in water, and have only 

 the most general ideas as to what they do 

 there or how they are distributed. It is 

 highly desirable that linniologists become 

 more interested in bacteria, and bacteriol- 

 ogists more interested in limnology. 



Our lack of knowledge of water bacteria 

 is due largely to a lack of interest on the 

 part of bacteriologists, who have been so 

 concerned witli the relations of bacteria to 

 disease, agriculture, and industry that they 

 have paid but little attention to bacteria of 

 no "practical" importance. Most of the 

 work on bacteria in water has been carried 

 out either from the standpoint of potability 



(the occurrence of disease-producing bac- 

 teria in the water) or from tlie stand- 

 point of pollution (the self-purification of 

 streams). Only a scattered few have done 

 any work on the bacteria characteristic of 

 the fresh water itself. The culture media 

 used for the study of bacteria of medical 

 importance are not suitable for the cultiva- 

 tion of the autochtlionous water bacteria, 

 and from the work of public health bac- 

 teriologists there developed an idea that 

 there are no bacteria characteristic of 

 water. The introduction of sodium casein- 

 ate (Xiihrstolf Ileyden) medium by Diig- 

 geli (1924) and by Fred, Wilson, and 

 Davenport (1924), provided indications 

 that there are true water bacteria, i.e., 

 species not derived from the surrounding 

 soil or other pollution. During the past 

 15 years there has developed a slowly-grow- 

 ing literature on lake bacteria as such. 

 This literature has been reviewed by Baier 

 (1935). Only certain papers will be 

 referred to here. 



We incline toward the vicAV that the main 

 function of bacteria in lakes must be the 

 decomposition of dead organic matter, lead- 

 ing to a mineralization of the elements com- 

 posing this organic matter, so that these ele- 

 ments are again available to photosyn- 

 thetic plants for the synthesis of new or- 

 ganic matter. Thus the lake bacteria link 

 the ends of the food-chain, convert it into 

 a cycle. 



But this is not the only role of bacteria 

 in lakes, and may not be the most important 

 one. Our knowledge of bacteria in all habi- 

 tats has been obtained through the use of 

 artificial culture media, tlie composition of 

 which (mainly organic) has been deter- 

 mined by habit established in studying bac- 

 teria of medical importance. Thus we 

 know best the luierotrophic bacteria, those 

 that obtain their energy by the oxidation 



39 



