Transcriptome analysis and quantification of microaerobic growth of Geobacter sulfurreducens

Geobacter sulfurreducens was originally considered a strict anaerobe. However, this bacterium was later shown to not only tolerate but also to use oxygen as terminal electron acceptor. Research performed has so far only revealed the general ability of G. sulfurreducens to reduce oxygen, but the oxygen consumption rate has not been quantified, nor has evidence been provided as to how the bacterium achieves oxygen consumption. The microaerobic growth of G. sulfurreducens under more controlled operating conditions was investigated here and a transcriptome analysis was performed to elucidate possible metabolic mechanisms important for oxygen consumption in G. sulfurreducens. The experiments revealed that growth with oxygen is possible to the same extent as with fumarate when a maximum oxygen load per cell of 95 mgO2gcdw-1h-1 is applied. When oxygen concentrations are too high, growth is completely inhibited and there is no partial consumption. Transcriptome analysis suggests a menaquinol oxidase to be the enzyme responsible for oxygen reduction. Transcriptome analysis has further revealed three different survival strategies, depending on the oxygen concentration present. When prompted with small amounts of oxygen, G. sulfurreducens will try to escape the microaerobic area; if concentrations are higher cells will focus on rapid and complete reduction; and ultimately cells will form protective layers if a complete reduction becomes impossible. The results presented here have important implications for understanding how G. sulfurreducens survives exposure to oxygen. Geobacter sulfurreducens was grown in minimal medium containing 10 mM acetate under anaerobic and aerobic conditions. Cultivations were performed with three biological replicates. Samples were taken during the late growth phase from cultures exposed to 1%, 3% or 5% of oxygen. Reference for transcriptome analysis were samples taken from anaerobic cultivations.