Distribution and Function of Marine Bacteria 43 



the basis of the microorganisms present. Comparing the open wa- 

 ters of tlie Mediterranean with other parts of the world, the 

 counts of heterotrophes are higher than those of the Antarctic and 

 Arctic regions of the world ocean. They are slightly below those 

 of the sub-tropics and the tropics of the Indian Ocean and of the 

 Black Sea. Since the river discharge into the Mediterranean is 

 small, it must be assumed that the source of nutrients for sapro- 

 phytic bacteria is the phytoplankton produced in the sea itself. 

 Thus the considerable number of saprophytic bacteria suggests 

 that the Mediterranean Sea is not as poor in plant life as had some- 

 times been suggested, and in this conclusion the authors support 

 recent direct observations on phytoplankton productivity, which 

 show that the southern part of the Mediterranean has phytoplank- 

 ton equal to that of the oceans generally. 



In several subsequent papers attention was turned to the 

 capacity of sea water to support or inhibit micro-organisms, and 

 to additives which might be favourable for growth. Because of 

 technical difficulties, little is known about the growth of bacteria 

 in extremely dilute media like sea water. The establishment of 

 satisfactory systems for steady state enrichment culture should 

 provide an optimum system for the development and calibration 

 of methods for enumerating and isolating significant micro-organ- 

 isms. This approach also shows promise in investigation of the 

 interactions of bacteria with phytoplankton and zooplankton, and 

 in relating bacterial numbers to their activities under natural 

 conditions. 



Palmer and Ordal* grew Sphaerotihis abundantly in a per- 

 fusion of tap water containing glucose, mineral salts and am- 

 monia. Thiothrix, however, would not grow in a perfusion similar 

 to its own spring water. As to marine organisms, although the 

 continuous cultures bring up forms which look like nitrifying 

 bacteria, the selection of characteristic population types has not 

 so far been very successful. 



Jannasch (Chapter 51) has applied the continuous culture 

 procedure of Novick and Szilard, using both dilute artificial 

 media and natural sea water. The organism was a Spirillum, isola- 



* Paper presented - Steady state enrichment cultures of acquatic and marine 

 microorganisms. 



