Chapter VIII —117— Marine Bacteria 



growth of marine chromogenic bacteria which develop at o° C. P^rom 

 the skin of the discolored halibut he isolated various yellow, orange, red, 

 and pink bacteria, some of which grew at temperatures as low as —5° C. 

 Further reference is made to the extensive literature on chromogenic bac- 

 teria which discolor marine fish on page 190. 



Snow and Fred (1926) found that, except during the period of gross 

 contamination, chromogenic bacteria constitute a high percentage of the 

 microflora indigenous to Lake Mendota. An average of 52 per cent of the 

 bacterial colonies were white or cream-colored, 35 per cent were yellow or 

 orange, and 11 per cent were pink or red. Blue, violet, green, and black 

 colonies were noted only infrequently. Snow and Fred contrast these 

 findings with the percentage of chromogens of all of the Eubacteriales 

 from various habitats described in the 1923 edition of Bergey's Manual of 

 Determinative Bacteriology: 18 per cent white or cream, 18 per cent yel- 

 low or orange, and 9 per cent pink or red. Only 3 per cent of the soil bac- 

 teria listed in the Bergey Manual produced red or pink pigments as com- 

 pared with 19 per cent of the salt-water bacteria and 23 per cent of the 

 fresh-water bacteria which were described as red or pink pigment pro- 

 ducers. 



Considerably more work should be done on the factors which influence 

 pigment production and the ecological significance of chromogenesis. 

 However, the attractiveness of the more perspicuous chromogens should 

 not influence one to overlook the less distinctive achromic varieties. 



Nearly all of the bacteria isolated from sea water or marine mud have 

 proved to be facultative aerobes. They grow better in the presence than 

 in the absence of atmospheric oxygen under ordinary conditions of labo- 

 ratory cultivation. Neither strict aerobes nor strict anaerobes are com- 

 mon in the sea, whereas both are fairly common in soil. The facultative 

 aerobes tend to lose their ability to grow anaerobically after prolonged 

 laboratory cultivation. These are provisional generalizations concerning 

 the relationship of marine bacteria to oxygen, and may be subject to mod- 

 ification when more information is available. 



Physiological characteristics : — Reference has already been made to 

 the physiological versatility of marine bacteria. It is believed that there 

 are bacteria in the sea which are capable of attacking nearly any kind of 

 organic substrate, and many inorganic compounds are altered by the 

 activities of marine microorganisms. The same may be said of soil and 

 fresh-water microorganisms, although there are certain gross dissimilari- 

 ties. 



As a group, marine bacteria are more weakly saccharolytic and prob- 

 ably more strongly proteolytic than are either soil or fresh-water bacteria. 

 Whether these properties are influenced by the salinity of the medium or 

 whether they are peculiar adaptations of certain autochthonous species is 

 problematical. Certainly the dissimilarities do not apply to individual 

 species. 



Although ZoBell and Grant (1943) present evidence which suggests 

 that all heterotrophic marine bacteria are able to assimilate glucose, only 

 46 of the 60 cultures studied by ZoBell and Upham (1944) fermented 

 glucose with the formation of acid, and none of them produced "gas" 

 from glucose. This may be due to a general lack of fermentative ability, 

 but more likely it is due to the efficiency of the organisms in assimilating 

 utilizable organic matter. When cultivated in dilute solutions, the marine 



