Anoxia in Ralstonia eutropha H16

Ralstonia eutropha H16 is a denitrifying microorganism able to use nitrate and nitrite as terminal electron acceptors under oxygen deprivation. To identify proteins showing an altered expression pattern in response to oxygen supply, R. eutropha cells grown aerobically and anaerobically were compared in a comprehensive proteome and transcriptome approach. Nearly 700 proteins involved in several processes including respiration, cell appendages formation, DNA and cofactor biosynthesis were found to be differentially expressed. A combination of 1D-gel-LC and conventional 2D-gel analysis of six consecutive sample points covering the entire denitrification sequence revealed a detailed view on the abundance pattern of the key proteins of denitrification. Denitrification- or anaerobiosis-induced alterations of the respiratory chain included a distinct expression pattern for multiple terminal oxidases. Alterations of the central metabolism were restricted to a few key functions including the isoenzymes for aconitase and isocitrate dehydrogenase, respectively. Although R. eutropha is a strictly respiratory bacterium, the abundance of certain fermentation enzymes was increased. This work represents a comprehensive survey of denitrification on proteomic and transcriptomic level and provides unique insight into how R. eutropha adapts its metabolism to low oxygen conditions.