Chapter V — 85 — Distribution in the Sea 



surfaces were not particularly beneficial. By adsorptive concentration of 

 nutrients, solid surfaces enable bacteria to develop in substrates otherwise 

 too dilute for growth. 



Besides concentrating nutrients, solid surfaces in sea water provide 

 surfaces for the attachment of sessile bacteria. The sessile habit of aquatic 

 bacteria is the basis of the submerged slide technic employed by Henrici 

 (1933, 1936), ZoBell and Allen (1933, 1935), Hotchkiss and Waksman 

 (1936), Smith and ZoBell (1937), and others for the direct microscopic 

 enumeration of bacteria. Kusnetzowa (1937) believes that all water bac- 

 teria are capable of attaching themselves to glass, and that many of them 

 grow only when attached to solid surfaces. Several species of bacteria 

 which grow only when attached to firm substrates have been described by 

 Henrici and Johnson (1935), ZoBell (19436), and ZoBell and Upham 

 (1944). Most of the bacteria in bottom deposits appear to be adsorbed 

 on or attached to particles of sediment (Waksman and Vartiovaara, 



1938).. 



Solid surfaces retard the diffusion of exoenzymes and partially digested 

 food away from bacteria. Large molecules of organic matter must be con- 

 verted into soluble substances by bacterial exoenzymes before the food 

 can be assimilated by bacteria. Consequently in a dilute nutrient solution 

 such as sea water, free-floating bacterial cells may not be able to digest 

 and absorb enough nutrient to provide for their organic requirements. 

 However, when the bacterial cells and organic nutrients are juxtaposed on 

 solid surfaces, the bacteria may more effectively absorb the food which 

 has been rendered soluble by their exoenzymes. Bacteria in an anchored 

 position are less influenced by molecular bombardment (with the resultant 

 Brownian movement and diffusion) which would tend to separate them 

 from their exoenzymes and hydrolyzates. Also, solid surfaces probably 

 facilitate the orientation of exoenzymes in the most advantageous posi- 

 tion, thereby increasing their stability and activity. 



The beneficial effects of solid surfaces in dilute nutrient solutions help 

 to explain why marine bacteria generally occur intimately associated with 

 solid particles, as has been shown by the work of Lloyd (1930), Waksman 

 et al. (1933c), and others. In considering the factors which influence the 

 distribution of bacteria in natural waters, Prescott and Winslow (193 1) 

 emphasized that in natural waters bacteria are to a great extent attached 

 to large solid particles. Inert particles appreciably smaller than bacteria 

 are not beneficial to bacteria; they may even be injurious to bacterial 

 activity (ZoBell, 19436). Other evidence for the attachment propensi- 

 ties of aquatic bacteria is reviewed on pages 56 and 193. 



Effect of sedimentation : — After stressing the importance of the low 

 concentration of organic nutrients in sea water as a factor which limits the 

 marine bacterial population, Renn (19376) declared that, "Particulate 

 substrates, necessary for the favorable development of large attached 

 populations, tend to settle and carry large numbers of bacteria into the 

 mud during sedimentation." Thus, while the affinity of solids for bacteria 

 tends to promote bacterial multiplication in dilute nutrient solutions, solid 

 particles whose density exceeds that of sea water also tend to reduce the 

 bacterial population. 



Frankland and Frankland (1894) concluded that sedimentation is 

 of the utmost importance in the purification of water. Jordan (1900) re- 

 garded it as noteworthy that in all the instances recorded in the literature 



