ACTION OF CYCLOSERINE ON A SPECIES OF ERWINIA WITH REFERENCE TO CELL DIVISION.

D-Cycloserine not only strongly inhibited ~rowth of an Erwinia species, but, at levels allowing some growth, inhibited cell division. The resulting long cells often showed thickening or swelling. Several agents were able to prevent this effect. D-Alanine, at a level that overcame growth inhibition completely, still allowed considerable elongation to take place. To overcome division inhibition completely required an approsimately 300-fold higher concentration than that completely overcoming growth inhibition under the conditions used. Similar results were obtained with L-alanine, but at a given concentration it was less effective than D-alanirle. Pantoyl lactone partially overcame growth inhibition, and, at higher levels which reduced growth, completely overcame division inhibition. Pyridoxal overcame growth inhibition to a large estent, but increased elongation and darnage to cells. Pantoyl lactone and L-alanine showed a high clegree of synergism in overcoming both growth and division inhibition by D-cycloserine. Pantoyl lactone plus D-alanine, or pyridosal plus either D- or L-alanine also showed such a synergism, but to a lesser extent. The signihcance of these findings with regard to known enzyme inhibitions of D-cycloserine is discussed.