Project description:Geobacter sulfurreducens is a dissimilatory metal-reducing bacterium capable of forming thick electron-conducting biofilms on solid electrodes in the absence of alternative electron acceptors. The remarkable ability of such biofilms to transfer electrons, liberated from soluble organic electron donors, over long distances has attracted scientific interest as to the mechanism for this process, and technological interest for application to microbial fuel and electrolysis cells and sensors. Here, we employ comparative proteomics to identify key metabolic pathways involved in G. sulfurreducens respiration by planktonic cells versus electron-conducting biofilms, in an effort to elucidate long-range electron transfer mechanisms.
Project description:We gained insights into the environmental controls of Geobacter activities in cobamide-driven microbiomes by investigating the adaptive responses of the model representative G. sulfurreducens to growth and reproduction in the presence of CoII. Consistent with environmental exposure, we demonstrate high CoII resistance in this species and describe from genomic rand transcriptomic data multiple pathways for protein and DNA repair, cell envelope modifications, and biofilm formation that allow the cells to effectively cope with CoII stress. Importantly, we show that metal acclimation also involves respiratory chains for the reductive precipitation of the metal on the cell’s surface. These adaptive responses allow Geobacter species to grow in CoII-rich environments, sustaining the productivity of the native microbiomes and contributing to hitherto abiotic reactions of the Co cycle.
Project description: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.
