Utilization of Serine by Clostridium botulinum. ∗

A number of amino acids are utilized by washed suspensions of Clostridium botulinum, for the most part in coupled reactions between pairs of different amino acids. 1 2 For example, alanine is deaminatively oxidized to CO₂ and acetic acid by glycine or proline which are reduced to acetic acid or δamino-n-valeric acid, respectively. However, amino acids such as leucine and particularly serine appeared to be deaminated when present singly in washed suspensions of this organism. The utilization of serine has been studied in detail by the technic already described, 3 ammonia being determined by the method of Parnas as described by Niederl and Niederl. 4 Serine is decarboxylated in the presence of washed suspensions of Types A or B Cl. botulinum at a rate (Qco₂ of 7-10) approximately one-third of that observed with pyruvic acid (Qco₂ of 25-30) as the substrate at optimal pH values for both reactions. Typical results of CO₂ production are presented in Fig. 1.

It is apparent that the pH optimum for the utilization of serine by Cl. botulinum lies on the alkaline side of neutrality, probably near pH 7.5. This is in marked contrast with the pH optimum of 6.0 observed with pyruvic acid as the substrate. In further studies it was observed that apparently only one optical form of serine is attacked at an appreciable rate, deamination and decarboxylation of dl-serine proceeding only approximately 50% to completion.

In semimacro experiments in Warburg vessels of 40 ml capacity with Clerici fluid in the manometers the fermentation was studied in more detail. Ammonia, CO₂, ethyl alcohol and acetic acid were identified as the chief products of degradation of serine. In these experiments the reaction was not allowed to go to completion due to the slow rate observed by the time approximately one-half of the serine had been utilized.