ZoBell 



98 — 



Marine Microbiology 



ing bacteria have never been observed in water, and others isolated from 

 water have not been found in mud. Unfortunately there are not enough 

 data on this point to be statistically significant. In general, the colonies 

 developing from marine mud are smaller, grow more slowly, and are less 

 likely to be pigmented than those developing from sea water. 



BuTKEViCH (19326), who demonstrated from 100 to 1000 times as 

 many bacteria in mud from the Barents Sea by direct microscopic counts 

 as by plate counts, expressed the opinion that most bacteria in bottom 

 deposits are spore formers. He detected numerous nitrate reducers and 

 sulfate reducers to depths of 30 to 40 cm. Most of the bottom-dwelling 

 bacteria were able to reproduce at —3° to —7° C. Rubentschik and 

 Chait (1937) estimated that from 6.2 to 13.3 per cent of the bacteria in 

 mud occur as spores. The bacteria observed by Butkevich (1938) in 

 muds of the Caspian Sea were almost exclusively spores below a mud depth 

 of 20 cm. 



The physiological versatility of microorganisms occurring in bottom 

 deposits is indicated by the large variety of substrates which are attacked. 

 The relative numbers of different physiological types of bacteria given in 

 Table XXIX were determined by the minimum dilution method, the 

 number being expressed as the reciprocal of the highest dilution in which 

 there was activity in the differential media. A plus sign (+) indicates that 

 the bacteria were demonstrated in the sample but that their numbers were 

 not determined. 



Table XXIX. — Relative numbers of different physiological types of bacteria demonstrated 

 in the topmost 3 to 5 cm. of three mud samples from the Pacific Ocean (ZoBell, igjSa):— 



Although their presence was not demonstrated in the analyses sum- 

 marized in Table XXIX, nitrogen-fixing and nitrifying bacteria have been 

 reported in marine bottom deposits (Cooper, 19376). Their significance 

 is discussed in Chapter XI. Carey and Waksman (1934) reported the 

 presence of nitrifying bacteria in mud samples collected from a water 

 depth of 4,742 meters in the Atlantic Ocean just north of Bermuda. 



Microorganisms which decompose lignin and hemicellulose were 



