Chapter XIV — 173 — Relation of Marine Bacteria 



The latter is named by Sanborn as a new species which resembles A. lilo- 

 raUs. Of the organisms Hsted above which were isolated from marine fish, 

 only A. ambiguion, Micrococcus nitrificans, and M. halophilus proved to be 

 salt-tolerant. They grew in media containing from lo to 20 per cent NaCl. 



Species of Achromohacter predominated in the slime of the 22 haddock 

 examined by Stewart (1932). She also observed species of Micrococcus, 

 Flavohacterium, Pseudomonas, and many unidentified luminescent bac- 

 teria in haddock slime. Nearly half of the cultures isolated from the 

 slime of II species of marine fish by Gibbons (1934a) were classified as 

 Achromohacter, with smaller numbers of Flavohacterium , Micrococcus, 

 Pseudonwnas, Bacillus, Proteus, and Serratia occurring in abundance in 

 the order listed. Luminescent bacteria have been commonly observed 

 growing on fish and other marine animals. Such bacteria are often asso- 

 ciated with the light organs of certain animals (Harvey, 1940). Addi- 

 tional data on the kinds of bacteria associated with marine fish are given 

 in Chapter XVI on page 188. 



Their predilection for solid surfaces and their organic requirements, 

 both of which are provided by animals, explain why certain bacteria are 

 intimately associated with animals. The secretions and excretions of an- 

 imals are a source of food for bacteria. The bacterial utilization of urea, 

 uric acid, and other waste products of animals is mutually beneficial to 

 both consumer and producer. 



Bacteria as food for animals : — Judging from their chemical composi- 

 tion, bacteria should be highly nutritious and readily digestible. This 

 supposition is substantiated by experimental and field observations which 

 indicate that many kinds of animals ingest bacteria. Certain animals can 

 live almost indefinitely on an exclusive diet of bacteria. 



Bacteria constitute an important part of the dietary of nearly all uni- 

 cellular animals, according to Luck et al. (193 1). They noted that Eu- 

 plotes taylori grew better on mixed cultures of bacteria than on any one 

 single strain. Heat-killed bacteria, filtrates, autolyzed bacteria, and 

 phage-lysed bacteria failed to support Euplotes taylori. The failure of cer- 

 tain bacteria to be assimilated by protozoans may be due to toxic meta- 

 bolic products, unfavorable size or shape, capsular material, or other 

 peculiarities. 



The importance of bacteria in the nutrition of pelagic copepods is 

 stressed by the work of Esterly (19 16) who considered the question of 

 the utilization of dissolved organic substances. He concluded that, al- 

 though unable to utilize dissolved materials directly, copepods may sub- 

 sist on bacteria which in turn utilize dissolved organic substances. Ac- 

 cording to Krizencky and Podhradsky (1927), one of the most impor- 

 tant functions of aquatic bacteria is the conversion of dissolved organic 

 matter into particulate (bacterial cell substance) organic matter which 

 animals can utilize. The ratio of dissolved to particulate organic matter 

 is estimated to range from 7:1 to 4000:1 in different parts of the ocean. 

 It is the consensus of opinion (Krogh, 1931; Fox and Coe, 1943) that, 

 contrary to Putter's theory, organic matter in true solution plays no 

 significant role in the direct nutrition of aquatic animals, but that bac- 

 teria serve as intermediary agents of vast importance. Given sufficient 

 time and favorable conditions, including solid surfaces, bacteria utilize 

 the organic content of sea water almost quantitatively (ZoBell and 

 Grant, 1943), mineralizing roughly 70 per cent of it and converting 30 

 per cent into bacterial cell substance or intermediate products. 



