PROTEOLYTIC ACTIVITIES OF SOIL MICROORGANISMS 481 



thus giving the total amino nitrogen present in the 100 cc. of the 

 filtrate. 



As a preliminary experiment, two quantities of Czapek's 

 solution were made up containing 0.5 per cent casein or peptone 

 in place of the NaNOs. The solutions were sterilized and 

 inoculated with A. niger, A. ochraceus B. mycoides, Act. penicil- 

 loides, and trypsin. The flasks were examined at the end of 1, 

 4, 7, 14 days for their amino nitrogen content. 



The figures in table 1 reveal marked differences in the 

 behavior of the different organisms. There is in all of the cul- 

 tures, with the exception of Act. penicilloides, an initial decrease 

 in the amino nitrogen content, which completely disappeared in 

 the case of A. niger growing on casein, when four days old. The 

 subsequent determinations show an increase in the amino 

 nitrogen. This seems to confirm the work of Sears (1916), who 

 has shown that the bacteria will first use the amino nitrogen 

 present in the medium and only later attack the protein and 

 split it into amino-acids. 



It was thought advisable to test a larger number of organisms 

 on peptone alone and obtain the amino nitrogen accmiiulation 

 (we can not speak of amino nitrogen production in cultures 

 where the growing organism was present, because a constant 

 utilization of the amino nitrogen takes place in the cultures). 

 Czapek's solution containing 2 per cent of peptone in place of the 

 NaNOs was used. The results are presented in table 2. 



On comparing the behavior of the different organisms in their 

 power to accumulate amino nitrogen, we are at once struck by 

 the action of B. mycoides and the two actinomyces used which 

 is so distinct from that of the molds. It is quite possible that the 

 molds were making a much more rapid growth than the bacte- 

 rium or actinomyces, the amino nitrogen formed being rapidly 

 used up by the organism or broken down to ammonia, or 

 that the last named organisms have a greater ability to decom- 

 pose the peptone into amino nitrogen compounds. On comparing 

 the accumulation of amino nitrogen with that of ammonia, we 

 find that there might be an indication of the fact that a great deal 

 of the amino nitrogen is broken down to ammonia, as is seen in the 



THE JOURNAL OF BACTERIOLOGY, VOL. Ill, NO. 5 



