ZoBell 



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Marine Microbiology 



lower population. These discontinuous zones corresponded exactly with 

 the loci of abrupt changes in the physical and chemical properties of the 

 sediments, a striking example of the relation between bacterial population 

 and environment. 



Representative data on the vertical distribution of bacteria in Minne- 

 sota and Wisconsin lake bottoms are summarized in Table XXVII. Car- 

 penter (1939) found a progressive decrease with depth in the bacterial 

 population of mud from Crystal Lake, an oligotrophic lake in northern 

 Wisconsin. Most of the organisms below the topmost layer of mud ap- 

 peared to be either anaerobes or facultative aerobes. 



Table XXVII. — Bacteria per ml. of lake mud jrom different depths as determined from 

 plate counts by HenricI and McCoy {1938): 



One of the longest cores on record was collected from the Gulf of Cali- 

 fornia by Emery and Dietz (1941), it being nearly 17 feet in length. To 

 obtain this core, the core barrel penetrated the bottom sediment to a 

 depth exceeding 25 feet. Plate counts made by microbiologists showed 

 that the bottom-most part of the core, as well as many other cores repre- 

 senting penetrations ranging from 10 to 20 feet, contained a minimum of 

 several hundred viable bacteria per gram (wet basis) . 



Lower limits of the biosphere : — Finding significant numbers of living 

 bacteria at such great depths, which represent geological ages of many 

 centuries, provokes the question: what is the lower limit of the biosphere? 

 From the extrapolation of the curves showing the abundance of bacteria in 

 sediments with depth, one might expect to find some bacteria at depths of 

 several hundred feet. 



In highmoor peat, which is a type of bottom deposit especially rich in 

 organic matter, Waksman and Stevens (1929) found bacteria in almost 

 undiminished numbers throughout the entire profile to the bottom of the 

 greatest depth examined, 510 cm. In ancient sediments which are now 

 above sea level, von Wolzogen Kuhr (1922) found sulfate-reducing bac- 

 teria at depths of 10 to 37 meters by rigorously collecting samples for bac- 

 teriological analysis from the walls of recent excavations. Sulfate reduc- 

 ers have also been recovered from oil-well brines, which are presumably 

 from ancient marine sediments, from depths exceeding a thousand feet by 

 Bastin (1926), Gahl and Anderson (1928), Bastin and Greer (1930), 

 Ginter (1930), Ginsburg-Karagitscheva (1933), and others. Of course, 

 it is questionable whether the sulfate reducers are indigenous to the oil- 

 well brines or were adventitiously introduced in the process of drilling the 

 wells. 



In their investigations to determine at what depths in the earth's crust 

 bacteria can live, Lieske and Hofmann (1929) found bacteria in coal at 

 a depth of 1089 meters. Lipman (193 i) reported the presence of living 



