The adaptation of bacterial cultures during the lag phase in media containing new substrates or antibacterial agents

Abstract

Of a series of seventeen experiments in which cells of Bact. coli mutabile and Bact. coli (K12) were allowed to lag in media containing all the materials necessary for growth and division, but with lactose and D-arabinose or dulcitol respectively as sole carbon sources there were eight experiments in which it was found, when samples were withdrawn at intervals during the lag phase and were plated on solid media containing the same carbon source, that the longer the cells had remained in the liquid medium the shorter was the plate lag. Since the majority of the cells in the liquid culture took part in this response it is interpreted as an adaptation involving the bulk of the population and does not represent the selection of a few mutant cells. In the other nine experiments the reduction in lag was also observed, but since the growth of the culture took place almost simultaneously with this reduction it was not possible to draw any definite conclusion from them. In another experiment involving the adaptation of Bact. coli mutabile to resist chloramphenicol a definite adaptive response was again obtained. Similar experiments in liquid media lacking a nitrogen source or in phosphate buffer show that the adaptation of Bact. coli mutabile to lactose and to chloramphenicol, and that of Bact. lactis aerogenes to D-arabinose in the presence of streptomycin can also go a considerable way in media which do not contain all the materials necessary for growth and division. Here again it is not necessary to postulate the presence of special mutant cells.