Adaptation to trichodermin and anisomycin in Physarum polycephalum

Trichodermin esterase activity and trichodermin resistance in Mucor racemosus

Mucor racemosus exhibited inducible phenotypic resistance toward the protein synthesis inhibitor trichodermin. Induction of resistance was elicited by exposure to trichodermin or to cycloheximide. Both adapted and nonadapted cells took up [14C]trichodermin from the medium. Trichodermin was found to be rapidly deacetylated to trichodermol upon entering the cell. Adapted cells deacetylated the drug more rapidly than nonadapted cells both in vivo and in vitro. The trichodermol resulting from deacetylation appeared in the medium, but the growth of adapting cells began well before the total conversion of trichodermin to trichodermol. Based on these data and the observation that trichodermol was a poor inhibitor of Mucor, adaptation appears to result from deacylation of the active antibiotic.

Anisomycin sensitive mutants of Physarum polycephalum isolated by cyst selection

The haploid myxamoebae of Physarum polycephalum reversibly differentiate to form dormant microcysts under conditions of starvation. The thin-walled cysts can be selective recovered from a cell suspension which has been treated with the surfactant Triton X-100 to lyse amoeboid forms. Excystment, which is initiated by suspension in liquid medium, is inhibited by antibiotics which block protein synthesis. Cysts of drug resistant mutants excyst rapidly in media containing sufficient antibiotic to maintain drug sensitive strains in the encysted state. The selective survival of non-excysted cells following Triton X-100 treatment has been employed to enrich for drug sensitive mutants. Several anisomycin sensitive mutants have been isolated, one of which has been analysed genetically. The possible applications of this mutant enrichment technique are discussed.