MERCURY RESISTANCE IS ENCODED BY TRANSFERABLE GIANT LINEAR PLASMIDS IN 2 CHESAPEAKE BAY STREPTOMYCES STRAINS

The Streptomyces strains CHR3 and CHR28, isolated from the Baltimore I nner Harbor, contained two and one, respectively, giant linear plasmid s which carry terminally bound proteins. The plasmids pRJ3L (322 kb), from CHR3, and pRJ28 (330 kb), from CHR28, carry genes homologous to t he previously characterized chromosomal Streptomyces lividans 66 opero n encoding resistance against mercuric compounds. Both plasmids are tr ansmissible (without any detectable rearrangement) to the chlorampheni col-resistant S. lividans TK24 strain lacking plasmids and carrying a chromosomal deletion of the mer operon. S, lividans TK24 conjugants ha rboring pRJ3L or pRJ28 exhibited profiles of mercury resistance to mer curic compounds similar to those of Streptomyces strains CHR3 and CHR2 8.