Grula, E. A. (Oklahoma State University, Stillwater) and Mary M. Grula. Cell division in a species of Erwinia. III. Reversal of inhibition of cell division caused by d-amino acids, penicillin, and ultraviolet light. J. Bacteriol. 83:981–988. 1962.—Inhibition of cell division in an Erwinia sp. occurs in the presence of any of six d-amino acids, penicillin, or ultraviolet light. Cell-division inhibition caused by d-amino acids is pH-dependent; however, elongation caused by penicillin occurs over a wide range of pH. Bulging and spheroplast formation in the presence of penicillin occurs only at pH values below 7.6; however, division continues to be inhibited at higher pH levels. Reversal of cell-division inhibition caused by two d-amino acids (phenylalanine and histidine) can be partially overcome by their respective l-isomers. Divalent cations (Zn, Ca, Mn) cause varying amounts of reversal of division inhibition in all systems studied; each system appears to have an individual requirement. All induced division inhibitions, including that caused by penicillin, can be reversed by pantoyl lactone or ω-methylpantoyl lactone. Evidence is presented and discussed concerning the possible importance of pantoyl lactone and divalent cations in terminal steps of the cell-division process in this organism.