A physical map of the megaplasmid pHG1, one of three genomic replicons in Ralstonia eutropha H16

We have used pulsed Field gel electrophoresis and megabase DNA techniques t o investigate the basic genomic organization of Ralstonia eutropha H16, and to construct a physical map of its indigenous megaplasmid pHG1. This Gram- negative, soil-dwelling bacterium is a facultative chemolithoautotroph and a denitrifier. In the absence of organic substrates it can grow on H-2 as i ts sole energy source and CO2 as its sole source of carbon. Under anaerobic conditions it can utilize nitrate as a terminal electron acceptor, whereby dinitrogen is released. Essential genetic determinants of the enzyme syste ms responsible for these metabolic processes are linked to the 0.44-Mb conj ugative megaplasmid pHG1. Aside from pHG1, the genome of R. eutropha H16 is comprised of two circular chromosomes measuring 4.1 and 2.9 Mb, adding up to a total genome size of 7.1 Mb. An estimated five copies of rDNA are dist ributed on the two chromosomes. A macrorestriction map of pHG1 was derived for the endonucleases Dra1 and XbaI. Hybridization studies showed that gene s for anaerobic metabolism are located on all three genomic replicons. (C) 2001 Federation of European Microbiological Societies. Published by Elsevie r Science B.V. All rights reserved.