CHAPTER VIII 

 BACTERIAL ASSOCIATIONS 



W. L. HOLMAN 

 University of Toronto 



INTRODUCTION 



Bacterial association has taken in recent years a much more important place in 

 bacteriological studies than formerly. This increased interest is largely due to the 

 greater attention which is being given to the finer metabolism of bacteria and the in- 

 teractions which occur between the bacteria and their environment. The idea long 

 held by many that bacteria represent the lowest forms of life and are therefore com- 

 paratively simple in their metabolic activity has been replaced by a realization that 

 we are dealing with just as highly specialized and complicated functional activities 

 as in any of the so-called "higher" plants or animals. It is true that we are dealing 

 with unicellular forms of very small size and that these as suggested by Kendall' 

 should be considered as similar to living colloids in which surface phenomena are so 

 important. Many of the activities in the life of the bacteria can be appreciated better 

 if this complicated metabolism is kept in mind, and the study of mixed or double cul- 

 tures helps in an understanding of the actual life-processes. 



NOMENCLATURE 



It is generally recognized but often forgotten that under natural conditions mixed 

 cultures are the rule, and the earliest work on bacterial associations is to be found 

 largely in the studies which attempted to analyze such natural phenomena. The most 

 variable results may be obtained in these mixed cultures, and there are many factors 

 taking part which determine the final outcome. There may be simple mixtures with 

 no demonstrable effect of one bacterium on another, but this is uncommon since one 

 or the other usually dominates the picture. One microbe may favor the growth and 

 activity of another or both may be benefited by the combination. The latter condi- 

 tion is usually spoken of as "symbiosis," but true examples of this relationship are 

 rare. The term "metabiosis" is sometimes used where one action follows another, and 

 is well illustrated in innumerable examples in nature. Antagonism or antibiosis is 

 often combined with the foregoing, but is mostly employed for the occurrences where 

 there is a clearly demonstrable harmful effect of one micro-organism on another or 

 when a characteristic product fails to be formed or disappears in the mixed culture. Be 

 cause of the impossibility in many cases of determining the actual processes at work 

 these terms must be used with reservations. It is better, I believe, to use the more 

 general word "association" for all these phenomena and "synergism," introduced into 

 bacteriological nomenclature by Kammerer,^ for those in which definite changes are 



' Kendall, A. I.: Colloid Symposium Monograph. 2, 195. 1925. 



^ Kammerer, H.: Klin. Wchnschr., 2, 1153. 1923; Deutschcs Arch.f. klin. Med., 141, 31S. 1923: 

 ibid., 145, 257. 1924; Klin. Wchnschr., z, 723. 1924. 



