Project description:Anode-associated multi-species exoelectrogenic biofilms are essential to the function of bioelectrochemical systems (BESs). The investigation of electrode-associated biofilms is critical to advance understanding of the function of individual members within communities that thrive using an electrode as the terminal electron acceptor. This study focusses on the analysis of a model biofilm community consisting of Shewanella oneidensis, Geobacter sulfurreducens and Geobacter metallireducens. The conducted experiments revealed that the organisms can build a stable biofilm on an electrode surface that is rather resilient to changes in the redox potential of the anode surface. The community operated at maximum electron transfer rates with electrode potentials of 0.04 V versus normal hydrogen electrode. Current densities decreased gradually with lower potentials and reached half-maximal values at -0.08 V. A positive interaction of the individual strains could be observed in our experiments. At least S. oneidensis and G. sulfurreducens show an upregulation of their central metabolism as a response to cultivation under mixed-species conditions. Interestingly, G. sulfurreducens was detected in the planktonic phase of the bioelectrochemical reactors only in mixed-culture experiments but not when it was grown in the absence of the other two organisms. It is possible that G. sulfurreducens cells used flavins which were released by S. oneidensis cells as electron shuttles. This would allow the organism to broaden its environmental niche. To the best of our knowledge, this is the first study describing the dynamics of biofilm formation of a model exoelectrogenic community, the resilience of the biofilm, and the molecular responses towards mixed-species conditions.
Project description:Lysinibacillus varians GY32 is a filamentous bacteria that can generate electricity in microbial fuel cells. To find potential genes participating in the electron transfer to electrode of Lysinibacillus varians GY32, we compared the gene expression profiles of this bacteria with yeast extract as electron donor and two electron acceptors, i.e. oxygen and electrode in microbial fuel cells. The results showed that several cytochrome c genes might play specific roles in the extracellular electron transfer to electrode in this strain.
Project description:Lysinibacillus varians GY32 is a filamentous bacteria that can generate electricity in microbial fuel cells. To find potential genes participating in the electron transfer to electrode of Lysinibacillus varians GY32, we compared the gene expression profiles of this bacteria with acetate as electron donor and two electron acceptors, i.e. oxygen and electrode in microbial fuel cells. The results showed that several cytochrome c genes might play specific roles in the extracellular electron transfer to electrode in this strain.
Project description:There is a wide diversity of potential applications for direct electron transfer from electrodes to microorganisms, which might be better optimized if the mechanisms for this novel electrode-biofilm interaction were better understood. Geobacter sulfurreducens is one of the few microorganisms available in pure culture that is known to be capable of directly accepting electrons from a negatively poised electrode. A microarray comparison of cells accepting electrons from the electrode versus cells donating electrons to the electrode reveals that the genes previously observed to be upregulated in current-producing biofilms are not highly expressed in current-consuming biofilms.
Project description:There is a wide diversity of potential applications for direct electron transfer from electrodes to microorganisms, which might be better optimized if the mechanisms for this novel electrode-biofilm interaction were further understood. Geobacter sulfurreducens is one of the few microorganisms available in pure culture that is known to be capable of directly accepting electrons from a negatively poised electrode. Gene transcript abundance in cells of G. sulfurreducens using electrons delivered from a graphite electrode as the sole electron donor for fumarate reduction was compared with transcript abundance in cells growing on the same graphite material, but without an electrical connection and acetate as the electron donor.
Project description:Transition of microbial growth from planktonic to biofilm is associated with programmed changes in the global patterns of gene expression. These changes are likely to faciliate the appropriate physiological and metabolic adjustments that bacteria need to make during the development of biofilms. Using microarrays we have examined the changes in pattern of gene expression associated with growth of Mycobacterium smegmatis in various stages of planktonic and biofilm cultures. Keywords: developmental time course
Project description:Biofilms are ubiquitous in natural, medical, and engineering environments. While most antibiotics that primarily aim to inhibit cell growth may result in bacterial drug resistance, biofilm inhibitors do not affect cell growth and there is less chance of developing resistance. This work sought to identify novel, non-toxic and potent biofilm inhibitors from Streptomyces bacteria for reducing the biofilm formation of Pseudomonas aeruginosa PAO1. Out of 4300 Streptomyces strains, one species produced and secreted peptide(s) to inhibit P. aeruginosa biofilm formation by 93% without affecting the growth of planktonic cells. Global transcriptome analyses (DNA microarray) revealed that the supernatant of the Streptomyces 230 strain induced phenazine, pyoverdine, and pyochelin synthesis genes. Electron microscopy showed that the supernatant of Streptomyces 230 strain reduced the production of polymeric matrix in P. aeruginosa biofilm cells, while the Streptomyces species enhanced swarming motility of P. aeruginosa. Therefore, current study suggests that Streptomyces bacteria are an important resource of biofilm inhibitors as well as antibiotics.
Project description:G. sulfurreducens can generate electricity from the oxidation of organic compounds. This is because it can take electrons from organic compounds and ship them out to the outer surface of the cell where they can then be deposited on various insoluble electron acceptors including electrodes. Cells attatched to the surface of an electrode oxidize acetate and and deposit the electrons derived from acetate onto the surface of the electrode after which they can travel through an electrical circuit, producing a current. Microbial fuel cells powered by acetate oxidation by Geobacter species are called Geobatteries. In this experiment we compared gene expression in a biofilm of the wild type strain growing on the surface of an electrode within a current-producing Geobattery to gene expression in a wild type biofilm that is not producing current, but is growing on the surface of an electrode. In both cases, the cells were growing in a flow-through two chambered H-cell Geobattery setup. This consists of two glass chambers, an anoxic anode chamber containing G. sulfurreducens, a graphite electrode, a reference electrode and growth medium and an oxic chamber containing the counter electrode. The two chambers are connected by a cation selective membrane and a wire connected to a potentionstat. A potentiostat is an instrument which maintains the redox potential of the anode at a fixed value relative to a reference electrode. Media continuously flowed through the anoxic anode chamber at a dilution rate of 0.15. In the experimental condition, the Geobattery was operational. The circuit was closed and G. sulfurreducens attached to the electrode generated current as it oxidized acetate. The redox potential at the anode was poised at 300 mV by the potentiostat. In the control condition, everything was the same, except that the medium in the anode chamber contained fumarate as electron acceptor, and the anode was not hooked up to the potentiostat i.e. the circuit was open. This prevented the anode from serving as an electron acceptor. Nevertheless a thick G. sulfurreducens biofilm grew on the surface of the electrode. The control and experimental geobatteries were harvested when current in the operational/experimental Geobatteries reached 10 mA. Keywords: two condition comparison