GENETIC-ANALYSIS OF ZWITTERMICIN-A RESISTANCE IN ESCHERICHIA-COLI - EFFECTS ON MEMBRANE-POTENTIAL AND RNA-POLYMERASE

Zwittermicin A is a novel aminopolyol antibiotic that represents a new structural class of antibiotic and has diverse biological activities, including the suppression of plant disease and the ability to inhibit prokaryotic and eukaryotic cells. To enhance our fundamental understa nding and applications of zwittermicin A, we elucidated mechanisms of zwittermicin A resistance in Escherichia coli. Two classes of zwitterm icin A-resistant mutants of E. coli were selected and characterized. O ne class included mutants altered in hemA, hemB, hemL, ubi, cydAB or a tp, which were defective in generating a proton motive force (PMF) and resistant to aminoglycosides. The mutant analysis, coupled with physi ological data, indicated an association between the electrical membran e potential (Delta Psi) component of PMF and zwittermicin A sensitivit y. A second class of zwittermicin A-resistant mutants was aminoglycosi de sensitive and was affected in rpoB and rpoC, genes that encode subu nits of RNA polymerase. The rpoB and rpoC mutants suggested that zwitt ermicin A might inhibit transcription, DNA replication, DNA gyrase or topoisomerase I; however, we found no further evidence to support any of these as the target for zwittermicin A. This study elucidated the g enetic mechanisms of zwittermicin A resistance in E. coli. The results suggest that Delta Psi drives zwittermicin A uptake, and that, unlike other antibiotics for which resistance maps in rpoB or rpoC, zwitterm icin A does not cause the rapid cessation of DNA or RNA synthesis, sug gesting a unique mechanism of antibiosis.