Distribution and Ecology of Azotobacter in the Black Sea 387 



and Spirillum always had a healthy appearance. Clostridium has 

 not been found in the water column of the deep-water regions. 

 In the region of the Zemov Phyllophora field and in the coastal 

 sites it has been found in lesser numbers than Azotobacter. 



The number of Azotobacter in muds is larger than in water. 

 It is seen from Table 2 that over 70 per cent of samples of the 

 sediment taken in coastal regions of the Black Sea contained more 

 than 2,380 to 23,800 cells and microcolonies of Azotobacter in 1 

 kg. In 30 per cent of the samples of the sediment, Azotobacter 

 has not been found. At the same time, in summer, i.e., in the 

 period of the maximum development of Azotobacter in water, 

 its greatest numbers were only more than 230 to 2380 per liter, 

 and they were found in smaller numbers of samples ( 50% ) in com- 

 parison with the muds. In the region of the Phyllophora field 

 and in coastal sites of the sea, strong wind disturbances mixing 

 the sediments sharply increased the content of Azotobacter, and 

 especially, Clostridium in water. After a durable calm, these 

 regions of the sea differ little from the deep-water regions in the 

 quantity of Azotobacter in water. In the coastal muds in zone 

 of HsS, Azotobacter occurs as often in the muds as in the "O2 

 zone." As the experiments showed, natural concentrations of H2S 

 had no lethal influence on Azotobacter. There are some reasons 

 to expect that in the coastal muds containing HjS, Azotobacter 

 can find some conditions for its development and fixation of 

 nitrogen, a method to increase the content of molybdenum and 

 natural radioactive elements, the presence of radiogenous oxygen 

 and some available sources of carbon (2, 7, 9). 



The microscopy of wash water and impresses from thallus 

 on slides showed that on the surface of Phyllophora there 

 exists a rich microbe population in the form of microcolonies, 

 pseudozooglea or diffuse accumulations consisting of cells mor- 

 phologically identical to Azotobacter and to some other micro- 

 organisms. The general number of bacteria obtained by the 

 method of direct microscopic count and their biomass per 1 kg. 

 of thallus was on the average, 439 billions of cells or 105.4 mg. 

 The numbers of Azotobacter obtained by the method of titres 

 varied from 2380 to 23,800 cells and microcolonies per kg of 

 fresh thallus. Clostridium occurs on Phyllophora more seldom 



