Enhancing electricity production in microbial fuel cells using defined co-cultures

Microbial fuel cells (MFCs) hold great promise for the simultaneous treatment of wastewater and electricity production. However, the electricity recovery is currently poor, typically <10% of what is theoretically possible, and the extracellular electron transfer mechanisms are poorly understood. The influence of using cocultures as a way of improving substrate turnover rate and hence electricity produced was investigated using synthetic wastewater as a substrate. Cocultures used were (i) Shewanella oneidensis and Clostridium beijerinckii; (ii) combinations of Geobacter sulphurreducens, Clostridium beijerinckii and Saccharomyces cerevisiae. The relative abundances test showed mutualistic relationship within the cocultures and was determined using RT-PCR at the end of the investigation. The coculture of S.oneidensis and C.beijerinkii gave a maximum power density of 87mWm-2 compared to 60 mWm-2 for C.beijerinckii alone and 48 mWm-2 for S.oneidensis alone. In the second study the best coculture combination was a mixture of Geobacter sulphurreducens, Clostridium beijerinckii and Saccharomyces cerevisiae giving a maximum power density of 80 mWm-2. Another study investigated the contribution of direct electron transfer mechanism on electricity production by physically separating Shewanella oneidensis to/from the anode electrode using a dialysis membrane. The outcome of this study indicated a maximum power output of 114±6 mWm-2 when cells were restricted close to the anode, 3.5 times more than when the cells were restricted away from the anode. Without the membrane the maximum power output was 129±6 mWm-2. These results highlight the importance of cocultures and direct electron transfer mechanism in improving electricity recovery in microbial fuel cells. Further work will seek to heterologously express the proteins in Shewanella involved in direct electron transfer in E.coli

Preasymptotic multiscaling in the phase-ordering dynamics of the kinetic Ising model

The evolution of the structure factor is studied during the phase-ordering dynamics of the kinetic Ising model with conserved order parameter. A preasymptotic multiscaling regime is found as in the solution of the Cahn-Hilliard-Cook equation, revealing that the late stage of phase-ordering is always approached through a crossover from multiscaling to standard scaling, independently from the nature of the microscopic dynamics.Comment: 11 pages, 3 figures, to be published in Europhys. Let

Lentiviral manipulation of gene expression in human adult and embryonic stem cells

Human stem cells could revolutionize the field of medicine by providing a diverse range of cell types for tissue replacement therapies and drug discovery. To achieve this goal, genetic tools need to be optimized and developed for controlling and manipulating stem cells ex vivo. Here we describe a lentiviral delivery system capable of high infection rates in human mesenchymal and embryonic stem cells. The lentiviral backbone was modified to express mono- and bi-cistronic transgenes and was also used to deliver short hairpin ribonucleic acid for specific silencing of gene expression in human stem cells. We show that lentiviral transduction can be used to alter gene expression without altering the genes' ability to differentiate in vitro. These vectors will enable rapid analysis of gene function in stem cells and permit the generation of knock-in / knock-out models of human disease in the rapidly developing field of gene therapy

Germination of Bacillus cereus spores in response to L-alanine and to inosine: the roles of gerL and gerQ operons

Bacillus cereus 569 (ATCC 10876) endospores germinate in response to inosine or L-alanine, the most rapid germination response being elicited by a combination of these germinants. The gerI operon has already been characterized as a homologue of the gerA spore-germination receptor family of operons found in all Bacillus spp. examined; the primary defect in gerI mutant spores is in the inosine germination response, although spores were also slower to germinate in L-alanine. Additional transposon-insertion mutants, from similar Tn917-LTV1 mutagenesis and enrichment experiments, now define two more operons, also members of the family of gerA homologues, important in L-alanine and inosine germination. Transposon insertions were identified in an alanine-specific germination locus, named gerL, which represents an operon of three genes, termed gerLA, gerLB and gerLC. By examining the residual germination response to L-alanine in gerI and gerL mutants, it was deduced that the GerL proteins contribute most strongly to the L-alanine germination response, and that the GerI proteins, required primarily in inosine germination, mediate only much slower germination responses to alanine. The L-alanine germination responses mediated by GerL and GerI proteins differ in their germination rates, temperature optima and germinant concentration dependence. The gerQ locus, again identified by transposon insertion, is a second inosine-related germinant-receptor operon. GerQ and GerI proteins are both required for the germination response to inosine as sole germinant, but GerQ has no role in L-alanine germination. Although near-identical homologues of gerI and gerL operons are evident in the Bacillus anthracis genome sequence, there is no evidence of a close homologue of gerQ

Enhancing electricity production from wastewater using microbial fuel cells

Microbial fuel cells represent a promising technology for simultaneous wastewater treatment and renewable electricity production. However, the electricity recovery is still poor, typically <10% of what is theoretically possible and the extracellular electron transfer mechanisms are poorly understood. The use of co-cultures to improve substrate (glucose) turnover rate and hence electricity recovered was investigated initially. A co-culture of Shewanella oneidensis and Clostridium beijerinckii gave a maximum power density (Pmax) of 87 mWm-2 (67% COD reduction) compared to 60 mWm-2 for C.beijerinckii alone and 48 mWm-2 for S.oneidensis alone. Co-culturing Geobacter sulphurreducens, C. beijerinckii and Saccharomyces cerevisiae gave the highest Pmax value of 80 mWm-2 (41% COD reduction) compared to other strain combinations. Another study investigated the contribution of direct electron transfer mechanism on electricity production by physically retaining Shewanella oneidensis cells close to or away from the anode electrode using a dialysis membrane (as well as immobilisation of the cells in alginate). Pyruvate was used as the substrate. The outcome of this study indicated a Pmax value of 114±6 mWm-2 when cells were retained close to the anode, 3.5 times more than when the cells were separated from the anode. Without the membrane Pmax was 129±6 mWm-2 (57% COD reduction). To understand the role played by c-type cytochromes MtrA, MtrB and MtrC in extracellular electron transfer in S.oneidensis, the genes mtrA, mtrB, mtrC and their combinations were heterologously expressed in non-electrogenic bacteria (Escherichia coli; glucose as substrate). The mtrCAB transformant gave the highest Pmax of 24 mWm-2 compared to 1 mWm-2 for the wild type although cell growth was slower. The results demonstrate the importance of co-cultures and of the MtrCAB pathway (direct electron transfer mechanism) in improving bacterial electricity production

Molecular and biochemical analysis of B. cereus 569 spore germination

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