Chapter VIII — 123 — Marine Bacteria 



The optimum temperature for maximum plate counts on marine ma- 

 terials was found by ZoBell and Conn (1940) to be 18° to 22° C. (see 

 Table IX on page 45). Unlike soil and fresh-water bacteria, very few 

 marine bacteria ordinarily grow at 30° to 37° C, and plate counts at 

 25° C. are significantly lower than those at 18° C. As many colonies of 

 marine bacteria may develop on plates of nutrient media incubated at 

 12° C. as at 22° C, but longer periods of incubation are required at the 

 lower temperature. 



While marine bacteria cannot be described as psychrophiles because 

 their optimum temperatures lie between 18° and 22° C, most of them 

 multiply slowly and are otherwise physiologically active at 0° to 4° C. 

 Their alDility to grow at near zero or sub-zero temperatures is not a unique 

 property of marine bacteria, since microorganisms from other habitats are 

 endowed with this ability, but it seems to be more common among marine 

 bacteria. Forster (1887) isolated from marine fish photogenic species 

 which reproduced at 0° C. Later Forster (1892) found that bacteria 

 capable of growing at low temperatures are quite widely distributed in 

 water and soil. Most of the photogenic bacteria isolated from the sea by 

 Fischer (1894a) grew at 0° C. From the water at Kiel, Fischer (18886) 

 isolated 14 species of bacteria which were capable of growing at 0° C. 



According to Hess (1932), autolysis of haddock muscle is almost neg- 

 ligible at 2.2° C. Bacterial decomposition was considerable at this tem- 

 perature and about half as rapid at — 1.1° C. 



Marine bacteria studied by Hess (1934a) grew readily at - 3° C, at 

 which temperature they were physiologically active and most intensely 

 pigmented. Some of them grew at - 6.5° C. It is difficult to study the 

 activities of organisms at temperatures lower than — 5° C. because, unless 

 solutes are added to the media to depress the freezing point, the water 

 crystallizes as ice. If a high concentration of solutes is added to the 

 media, the osmotic pressure is increased proportionately as the freezing 

 point is depressed, under which conditions it is indeterminate whether the 

 low temperature, the high osmotic pressure, or the specific effect of the 

 solute is the limiting factor. 



Hess (19346) reports that the optimum temperature for obtaining a 

 large crop of marine bacteria approaches 5° C. Larger crops were ob- 

 tained at 0° and - 3° C. than at 20° C. The bacteria multiplied more 

 rapidly at 20° C. than at 5° C. but they also died more rapidly at the 

 higher temperature. The bacteria were rapidly destroyed at 37° C. They 

 lived almost indefinitely in sea water at — 3° to 5° C. 



Sanborn (1930) described several species of marine bacteria which 

 cause the decomposition of fish fillets stored at — 5° C. Gibbons (1934c) 

 observed the bacterial decomposition of iced fillets at — 5° C. but not at 

 — 18° C. At the lower temperature most of the water is probably solidi- 

 fied as ice causing the arrest of bacterial activities. Stewart (1934) de- 

 cided that a refrigeration temperature of — 1 2° C. was necessary to inhibit 

 the growth of bacteria in fish muscle. She noted a rapid multiplication of 

 bacteria at — 3° C, and certain chromogens grew at — 6° C. Included in 

 her study were 9 species of Achromobacter, 13 species of Flavobacterium, 4 

 species of Micrococcus, and 3 yeasts. 



Eighty per cent of the cultures isolated from mackerel were found by 

 KiSER (1944) to produce macroscopically visible growth in six days at 

 o°C. From the growth curves of an Achromohacter species it was calcu- 

 lated that the minimum generation times were 0.98 hours at 25°C., 4.84 



