Genetics and Enzymology of Chloramphenicol Resistance

that growth on phenylacetamide could not be attributed to any residual activity of the aliphatic amidase. It seemed clear that the wild type P. putida A87 is capable of producing two separate amidases and carries genes for the structure and regulation of both an aliphatic amidase and an aromatic amidase. Similar conclusions were reached for P . cepacia strain 716. P.putida strain A90 was particularly interesting. It has proved impossible to detect any acetamidase activity in this strain and no acetamide-utilizing mutants have ever been isolated. However, it grows very well on phenylacetamide and thus resembles the acetamide-negative mutant of strain A87 and some of the phenylacetamide mutants of P . aeruginosa PACI. The phenylacetamidase of strain A90 has been purified and still gives no cross reaction with the P . aeruginosa aliphatic amidase antiserum. Further studies on these amidases may indicate whether the genes for the naturally occurring acetamidases and phenylacetamidases have a common ancestry or are of independent origin.