Occurrence and Significance of Chitinoclastic Bacteria 



605 



gic marine bacteria can be described as trtdy ubiquitous, but 

 their numbers at a given locus unpredictable. In the vast realms 

 of the sea they are nearly omnipresent, but in relatively low num- 

 bers, especially below the euphotic zone where there are but few 

 bacteria per ml of water. There seems to be a tendency, but not a 

 rule, for greater numbers to occur nearer the surface. The sparse- 

 ness of the bacterial populations is demonstrated in Table 4, 

 which indicates that in 82 per cent of one ml inocula of pelagic 

 seawater, the population found was less than ten cells per ml, 

 and in 93 per cent of the plates less than 50 cells per ml. As in- 

 dicated, 32 per cent of the samples contained no bacteria, but 

 rarely ( four times ) were replicates of a given water sample devoid 

 of bacteria. These figures are results from pour plating techniques, 

 and results from silica gel and molecular filter techniques gen- 

 erally show one to several orders of magnitude greater numbers 

 (14, 17). The difference is probably due to the heat necessarily 

 applied in the pour plating technique. 



TABLE 4 



Occurrence of Bacteria in Pelagic Waters^ Irrespective of Depth. 

 Ninety Plates, each with 1.0 ml. Inoculum 



No. of 



Plates % 



bacteria in 1 ml. 



1 — 10 bacteria in 1 ml. 



10 — 50 bacteria in 1 ml. 



50 — 100 bacteria in 1 ml. 



100—1000 bacteria in 1 ml. 



1000 bacteria in 1 ml. 



The high bacterial counts found in a few of the water sam- 

 ples, generally from the surface layers, can be attributed to the 

 periphytic association of bacteria on particulate matter as postu- 

 lated by ZoBell (28) and others. Wide discrepancies between 

 the counts on replicate plates were found in several instances, 

 which would further indicate sorption phenomena. It should ]u> 

 pointed out, in this connection, tliat the limiting orifice of tlie J-Z 

 water sampler was 3 mm, which miglit reduce numbers by selec- 

 ting against those adsorbed on larger particulate matter. 



