Chapter VIII — 115 — Marine Bacteria 



aquatic environments, but any generalizations must be preceded by more 

 extensive investigations. Pleomorphism appears to be more common 

 among marine bacteria than among the microllora of rivers, lakes, or soil. 

 About one-lifth of the Gram-negative "rods" occurring in the sea are 

 hehcoidal, being properly classitied as vibrio or spirilla. For the sake of 

 simplicity, both straight and helicoidal rods are grouped together in 

 Table XXXI since the investigators failed to mention vibrio or spirilla. 

 This may have been an oversight, although there are perhaps more vibrio 

 and spirilla in the sea than in soil or lakes. 



The majority of the bacteria found in the sea are actively motile. 

 Flagella have been demonstrated on between 75 and 85 per cent of the 

 pure cultures which have been examined, and a somewhat higher per- 

 centage have been reported as "motile." It is interesting to speculate 

 upon the preponderance of motile forms as a possible aquatic adaptation. 



Spore-forming bacteria do not appear to be particularly abundant in 

 the sea, although Newton (1924) has described the characteristics of 80 

 different pure cultures of heat-tolerant bacteria which she isolated from 

 the alimentary tracts of marine animals and from sea water. The ability 

 of the organisms to tolerate a temperature of 80° C. for ten minutes was 

 used as a criterion of spore formation. Twelve of her cultures survived 

 boiling for three hours. Most marine bacteria are notoriously heat sensi- 

 tive, as is discussed below. 



Marine spore-forming bacteria described by ZoBell and Upham 

 (1944) include Bacillus abysseus, B. borborokoites, B. cirroflagellosus, B.fili- 

 colonicus, B. imomarinus, B. submarinus, B. thalassokoites, and B. epi- 

 phyticus. All of these were isolated from mud except B. epiphyticus. It 

 was found associated with algae. 



On the average, marine bacteria are smaller than those which occur 

 in milk, sewage, fresh water, or soil. Fresh-water bacteria are smaller on 

 the average than soil forms. This generalization applies to representa- 

 tives of the sub-order Eubacteriineae. Sulfur bacteria and representatives 

 of the Chlamydobacteriales and Spirochaetales present many exceptions. 



Species of Pseudomonas, Vibrio, Flavobacterium, Achromobacter, and 

 Bacterium predominate in the sea in the order named. Representatives of 

 several other genera occur in smaller numbers (see Table XXXIV on 

 p. 124). This may be contrasted with the preponderance of species of 

 Bacillus and Actinomyces ordinarily found in soil. Due to their sanitary 

 significance in fresh-water bodies, the importance of the enteric bacteria 

 has been stressed by many investigators, but numerically they are out- 

 numbered by species of the aforementioned genera. 



Waksman (1934) writes, "The bacterial population of the sea is quite 

 characteristic. It is distinct in nature from the population usually found 

 on land, as shown by the more limited number of bacterial types found in 

 the sea. Spore-forming bacteria, which comprise an important part of the 

 bacterial population in soil, are practically absent in sea water, although 

 they may be present in considerable abundance in the sea bottom. Cocci 

 are also of limited occurrence in the sea. Motile rods and various types of 

 vibrios, or comma-shaped organisms, usually make up the major part of 

 the bacterial population thus far studied. The poverty of bacterial species 

 in the sea depends largely upon the specific nature of sea water as a me- 

 dium for the growth of these organisms." 



For further information concerning the morphology of marine bac- 

 teria the reader is referred to the literature summarized by ZoBell and 



