On the mechanism of resistance to channel-forming colicins (PacB) and tellurite, encoded by plasmid Mip233 (IncHI3)

Plasmids of the H incompatibility complex confer protection against all kno wn channel-forming colicins (PacB character) and resistance to potassium te llurite (Te-r) to Escherichia coli strains. A DNA clone (2.2 kbp) from plas mid Mip233 (IncHI3) expressing PacB-Te-r phenotypes was studied. DNA sequen ce analysis revealed a high degree of homology with the enzyme O-acetylseri ne sulfhydrylase. Size of the PacB-Te-r transcript was estimated as 1200 ba ses. A single polypeptide was found on SDS-polyacrylamide gel with a molecu lar mass estimated of 34 kDa. The effect of channel-forming colicins and te llurite was analyzed at physiological and transcriptional levels. Results s uggest that the pacB gene product could be a reductase-like enzyme. It is a lso suggested that presence of the PacB character among H plasmid confers s elective advantage on cells sharing an ecological niche. (C) 2000 Federatio n of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.