Final Technical Report

The work done with DOE support during this 15 year period was extensive and successful. It is best summarized by the list of 58 publications (below) which reported progress made with DOE support. These are from the grant period and a few more recent reporting on grant research. Mostly these are primary research reports in reviewed journals. There are also, however, many summary reviews in review journals and in scientific monographs, as they also are key places for reporting research progress. What we did during this grant period (and much longer) was to characterize genetic determinants for bacterial resistances to additional toxic heavy metals of DOE concern, through starting with phenotypic properties of the resistant bacteria to DNA sequence determination and characterization of the genes involved. Over the years (and as shown in the list of publications), the toxic metal-forming elements we have studied included Ag, As, Cd, Cr, and Hg. In each case, we started with basically nothing (or very little) known, progressed through quite detailed understanding, until other laboratory groups also became strongly involved in related studies. More recently, with DOE support, we were the first laboratory group in the world to identify genes for bacterial resistance to silver salts (sil genes) and the closely related silver-and-copper resistance genes cus. This was initially reported in detail in Gupta et al. (1999; see publications list below). We also identified the first toxic metal 'gene island' (multiple transcripts and perhaps 25 genes each in need of detailed study) which encodes the subunits of arsenite oxidase (which we called aso; Silver and Phung, 2005; but most other researchers have subsequently settled on aox for the gene mnemonic). Both of these systems were firsts. Now a few years later, a search on GenBank shows that each is now represented by gene families with more than a dozen examples that have been identified and sequenced. Most of the additional representative systems are from total bacterial genomes without specific gene characterization