John A. Leigh

Scholar: 1986

Awarded Institution
University of Washington
Department of Microbiology


Research Interests

My lab is interested in the regulation of gene expression in the methanogenic archaebacteria. These organisms belong to the archaeal domain of life which, though prokaryotic in cell structure, resemble eukaryotes in many of their molecular features. Besides the strictly anaerobic methane producers, the Archaea include the extreme thermophiles and the extreme halophiles. Compared to typical bacteria and eukaryotes, they represent a vastly understudied group. My group focuses on gene expression in two systems, nitrogen fixation and carbon dioxide fixation, in the marine methanogenic species Methanococcus maripaludis. Structural nitrogen fixation genes in M. maripaludis resemble those of typical bacteria, and carbon dioxide fixation proceeds by the carbon monoxide dehydrogenase pathway also found in certain anaerobes of the bacterial domain. However, genetic regulatory mechanisms are almost totally unknown. My group has cloned the genes for nitrogen fixation from M. maripaludis, and has worked out the genetic methodology to mutagenize these genes by transposon insertion mutagenesis. In this way a cluster of genes necessary for nitrogen fixation has been delineated. Potential regulatory regions have been identified and trans-acting regulatory genes are being sought. My lab also participates in the Marine Bioremediation Program at the University of Washington, and we are interested in the role of anaerobic bacteria in bioremediation. Our approach is two-pronged. First, we will manipulate the genes for carbon monoxide dehydrogenase in M. maripaludis to see if this enzyme can play a role in reductive dehalogenation. Secondly, we will study enrichments and isolates of methanogens, sulfate reducers, and other anaerobes from a contaminated site in Puget Sound with respect to their ability to carry out steps in the degradation of polyaromatic hydrocarbons and halogenated compounds.