Distributioji of Heterotrophic Bacteria 551 



1250, 1500, 2000, 2500, 3000, 3500, 4000 m.). A 40 ml sample 

 was passed through a membrane ultrafilter no. 2 and was grown 

 on a medimn of dry nutrient agar* (50 g per liter of sea water). 



RESULTS AND DISCUSSION 



A comparison of the Mediterranean regions investigated, 

 shows that the richest, according to the development of album- 

 inate-decomposing bacteria, are straits. The highest counts came 

 from the Otranto Strait and the next from the Strait of Tunis. The 

 largest numbers of bacteria were recorded in these two places; as 

 Table 1 shows, the sum of stations having 100 colonies and over 

 amounts of 81.7 per cent and 66 per cent respectively. This is 

 attributed to the strong current of the straits, since it is known that 

 where whirlpools fonn at the edge of currents, various organic 

 residues are readily accumulated, and such residues provide the 

 basis for the development of saprophytic bacteria (5-6-7-9-13). 

 The stations of the Otranto Strait show a higher number of bac- 

 teria at almost all depths, the maximum quantities of heterotrophs 

 (from 1000 to 2904) are found over the greater part of the 

 depths sampled. In the Strait of Tunis, bacterial numbers are 

 usually from 101 to 500; samples containing 501-1000 bacteria 

 being found relatively seldom, and only in one case were more 

 than 1000 (1100) bacteria counted. 



It should be noted that the highest counts of bacteria were 

 obtained at the 300 m horizon, next in order were the 100 m, 25 

 m, and the m levels. It is noteworthy that the greater develop- 

 ment of phytoplankton (from 1000 to 4000 Coccolithophorideae 

 per ml) near Sicily was found in Julv 1955 between 300 and 400 

 m (4). 



The Levant Sea and the Tyrrhenian Sea are approximately 

 equal as regards the quantitative development of heterotrophic 

 bacteria: in both seas half of the samples (40% and 49.3%) gave 

 from 51 to 500 bacteria; 3.1 per cent and 3.4 per cent gave from 

 501 to 1000, and about 3 per cent gave more than 1000 (to 1550). 

 In an equal number of cases (43.6 per cent and 44 per cent) the 

 minimum number of bacteria was recorded. In the Levant Sea, 



* The hydrolysate of fish meal obtained by working up with ferment trypsin (60% 

 hydrolysate, 40% agar-agar). 



