42 



PROBLEMS OF LAKE BIOLOGY 



ried out almost exclusively from a sanitary 

 standpoint, and the culture media used 

 were not suitable for the growth of charac- 

 teristic water bacteria. Seeing on their 

 plates only the same sorts of colonies that 

 grew on plates exposed to the air or inocu- 

 lated with dust or soil, they came to the 

 conclusion that bacteria in the water had 

 merely been brought there from the sur- 

 rounding land. It is true that some of the 

 early microscopists described and illus- 

 trated a number of bacteria from water 

 tliat are morphologically distinctive, and 

 obviously characteristic of the water. But 

 teachers and textbooks of bacteriology have 

 almost always dismissed these with the 

 simple statement that they cannot be culti- 

 vated in artificial media and are therefore 

 not important. They have usually been re- 

 ferred to rather vaguely as "higher" bac- 

 teria, outside the scope of true bacteriology. 



Huber-Pestalozzi (1938) has divided the 

 water bacteria into two groups — the mor- 

 phologically identifiable and those which 

 can only be identified by physiological 

 characters. The latter, of course, must be 

 grown in pure cultures for their final 

 identification. The morphologically identi- 

 fiable species, many of which have been de- 

 scribed and illustrated by Huber-Pestalozzi, 

 are very unusual to those acquainted only 

 with the cocci, bacilli, and spirilla of medi- 

 cal bacteriology. They fall in three orders : 

 the filamentous ensheathed Chlamydobac- 

 teriales, the sulphur bacteria or Thiobac- 

 teriales, and the recently discovered Caulo- 

 bacteriales (Henrici and Johnson 1935). 

 The latter grow in the water on stalks 

 similar to some diatoms and protozoa. 

 Some of the morphologically identifiable 

 water bacteria deposit iron in their sheaths 

 or on their stalks, or as capsules, in a char- 

 acteristic manner, which helps in their 

 recognition. The iron bacteria have re- 

 cently been monographed by Dorff (1934). 

 The Thiobacteriales have been described by 

 Bavendamm (1924). 



The species of water bacteria which re- 

 quire cultivation for their identification 

 have not been extensively studied. Aside 

 from the dominance of chromogenic species, 

 we have no clear evidence of an autochthon- 



ous flora of Eubacteriales in lakes. But it 

 is the author's opinion that this lack of evi- 

 dence is due merely to lack of investigation. 

 There is some scattered evidence that when 

 sufficient pure culture studies have been 

 made they will eventually show a true 

 aquatic flora of bacteria. Thus, Kluyver 

 and van Reenen (1933) have shown that in 

 Avater Azotohacter agilis is the important 

 nitrogen-fixing bacterium, not the Azoto- 

 hacter chroococcum commonly found in 

 soil. The genus Spirillum has long been 

 known as dominantly aquatic ; it has been 

 studied but little until recently Giesberger 

 (1936) contributed substantially to our 

 knowledge of both the physiology and tax- 

 onomy of the genus. 



I cannot too strongly emphasize our al- 

 most comiDlete lack of knowledge of the 

 taxonomy of water bacteria. Only a few 

 scattered groups have received any atten- 

 tion at all. To illustrate, the fourth edi- 

 tion of Bergey's Manual of Determinative 

 Bacteriology lists but 27 species of the 

 genus Corynebacterium, practically all of 

 them parasitic in animals. I have found 

 that about 15 per cent of all the bacteria 

 which may be cultivated from the bottom 

 deposits of lakes fall in this genus. They 

 belong to an unknown number of species, 

 none of which has as yet been described. 

 We may make but little progress in the 

 study of bacteria in relation to lake ecology 

 until bacteriologists become sufficiently in- 

 terested to work out the taxonomy of the 

 common lake bacteria. 



A lack of knowledge of the species of 

 water bacteria need not, however, entirely 

 impede studies of bacteria in relation to the 

 household of lakes. AVe may learn con- 

 siderable about the iDroductivity of lakes, 

 about the distribution of life in the lakes, 

 by simple quantitative determinations of 

 the plankton, without subjecting these to 

 taxonomic analysis. Similarly we may 

 study the distribution of the total bac- 

 terial flora in different tj'pes of lakes, 

 in different parts of lakes, and at different 

 seasons, and so gain some idea as to their 

 activities without determining the species. 

 Indeed such general surveys are desirable 

 before extensive taxonomic studies are 



