Project description:Our study revealed a synergistic effect between biological nitrogen fixation and current generation by G. sulfurreducens, providing a green nitrogen fixation alternative through shifting the nitrogen fixation field from energy consumption to energy production and having implications for N-deficient wastewater treatment.
Project description:The conductive pili of Geobacter sulfurreducens are essential for optimal extracellular electron transfer to Fe(III) and long-range electron transport through current-producing biofilms. The KN400 strain of G. sulfurreducens reduces poorly crystalline Fe(III) oxide more rapidly than the more extensively studied DL-1 strain. Deletion of the gene for PilA, the structural pilin protein, in strain KN400 inhibited Fe(III) oxide reduction. However, slow rates of Fe(III) reduction were detected after extended (> 30 days) incubation in the presence of Fe(III) oxide. After seven consecutive transfers the PilA-deficient strain adapted to reduce Fe(III) oxide as fast as the wild type. Microarray, proteomic, and gene deletion studies indicated that this adaptation was associated with greater production of the c-type cytochrome PgcA, which was released into the culture medium. It is proposed that the extracellular cytochrome acts as an electron shuttle, promoting electron transfer from the outer cell surface to Fe(III) oxides. The adapted PilA-deficient strain competed well with the wild-type strain when both were grown together on Fe(III) oxide. However, when 50% of the culture medium was replaced with fresh medium every three days, the wild-type strain out-competed the adapted strain. A possible explanation for this is that the necessity to produce additional PgcA, to replace the PgcA continually removed, put the adapted strain at a competitive disadvantage, similar to the apparent selection against electron-shuttling producing Fe(III) reducers in most soils and sediments. Despite increased extracellular cytochrome production, the adapted PilA-deficient strain produced low levels of current; consistent with the concept that long-range electron transport through G. sulfurreducens biofilms cannot be achieved without PilA-pili. An eight-chip study using total RNA recovered from four separate cultures of Geobacter sulfurreducens JS-1 (experimental condition) or Geobacter sulfurreducens KN400 (control condition) grown with acetate (10mM)-Fe(III) oxide (100 mmol l-1) exponential growth. Each chip measures the expression level of 3,328 genes from Geobacter sulfurreducens KN400 with nine 45-60-mer probe pairs (PM/MM) per gene, with three-fold technical redundancy.
Project description:The conductive pili of Geobacter sulfurreducens are essential for optimal extracellular electron transfer to Fe(III) and long-range electron transport through current-producing biofilms. The KN400 strain of G. sulfurreducens reduces poorly crystalline Fe(III) oxide more rapidly than the more extensively studied DL-1 strain. Deletion of the gene for PilA, the structural pilin protein, in strain KN400 inhibited Fe(III) oxide reduction. However, slow rates of Fe(III) reduction were detected after extended (> 30 days) incubation in the presence of Fe(III) oxide. After seven consecutive transfers the PilA-deficient strain adapted to reduce Fe(III) oxide as fast as the wild type. Microarray, proteomic, and gene deletion studies indicated that this adaptation was associated with greater production of the c-type cytochrome PgcA, which was released into the culture medium. It is proposed that the extracellular cytochrome acts as an electron shuttle, promoting electron transfer from the outer cell surface to Fe(III) oxides. The adapted PilA-deficient strain competed well with the wild-type strain when both were grown together on Fe(III) oxide. However, when 50% of the culture medium was replaced with fresh medium every three days, the wild-type strain out-competed the adapted strain. A possible explanation for this is that the necessity to produce additional PgcA, to replace the PgcA continually removed, put the adapted strain at a competitive disadvantage, similar to the apparent selection against electron-shuttling producing Fe(III) reducers in most soils and sediments. Despite increased extracellular cytochrome production, the adapted PilA-deficient strain produced low levels of current; consistent with the concept that long-range electron transport through G. sulfurreducens biofilms cannot be achieved without PilA-pili.
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.
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.