SEQUENCE CONSERVATION BETWEEN REGULATORY MERCURY RESISTANCE GENES IN BACTERIA FROM MERCURY POLLUTED AND PRISTINE ENVIRONMENTS

The regulatory gene merR, and the adjacent operator/promoter region wa s amplified from the mercury resistance (Hg-R) determinants from 10 Gr am-negative bacterial isolates from mercury polluted and pristine envi ronments using the polymerase chain reaction. These mer regions showed polymorphism in size of PCR amplfication products with those from iso lates SE3, SE11, SE12, SE31, SO1 and T217 being of 557 base pairs in s ize, whilst those from isolates SE20, T238, SB3, SB4 and the positive control (Tn501) were 536 base pairs in size. From the sequence analysi s of these mer regions and comparison with previously sequenced Hg-R d eterminants an evolutionary tree was constructed which showed there to be a significant difference between Gram- negative merR genes and tho se found in Gram-positive organisms. With the exception of the Thiobac illus Hg-R determinants, merR genes from Gram negative bacteria were s trongly conserved and could be grouped closely around the previously s equenced determinants of Tn501, Tn21, Tn5053 (pMER327/419) and pKLH2. Only the merR genes of pDU1358 and T238 showed significant variation f rom these subgroups. The regions of greatest Variation were the carbox yl terminal coding region of the merR gene and the operator/promoter r egion. It is suggested that, due to the global nature of inducible mer cury resistance and its strong sequence conservation across large geog raphical distances, bacterial resistance to mercury is an ancient gene tic character.