Reactors for microbial electrobiotechnology

From the first electromicrobial experiment to a sophisticated microbial electrochemical process - it all takes place in a reactor. Whereas the reactor design and materials used strongly influence the obtained results, there are no common platforms for MES reactors. This is a critical convention gap, as cross-comparison and benchmarking among MES as well as MES vs. conventional biotechnological processes is needed. Only knowledge driven engineering of MES reactors will pave the way to application and commercialization. In this chapter we first assess the requirements on reactors to be used for bioelectrochemical systems as well as potential losses caused by the reactor design. Subsequently, we compile the main types and designs of reactors used for MES so far, starting from simple H-cells to stirred tank reactors. We conclude with a discussion on the weaknesses and strengths of the existing types of reactors for bioelectrochemical systems that are scored on design criteria and draw conclusions for the future engineering of MES reactors. [GRAPHICS]

Solar-driven carbon dioxide fixation using photosynthetic semiconductor bio-hybrids.

Solar-driven conversion of carbon dioxide to value-added carbon products is an ambitious objective of ongoing research efforts. However, high overpotential, low selectivity and poor CO2 mass transfer plague purely inorganic electrocatalysts. In this instance, we can consider a class of biological organisms that have evolved to achieve CO2 fixation. We can harness and combine the streamlined CO2 fixation pathways of these whole organisms with the exceptional ability of semiconducting nanomaterials to harvest solar energy. A novel nanomaterial-biological interface has been pioneered in which light-capturing cadmium sulfide nanoparticles reside within individual organisms essentially powering biological CO2 fixation by solar energy. In order to further develop the photosensitized organism platform, more biocompatible photosensitizers and cytoprotective strategies are required as well as elucidation of charge transfer mechanisms. Here, we discuss the ability of gold nanoclusters to photosensitize a model acetogen effectively and biocompatibly. Additionally, we present innovative materials including two-dimensional metal organic framework sheets and alginate hydrogels to shield photosensitized cells. Finally, we delve into original work using transient absorption spectroscopy to inform on charge transfer mechanisms

Cosmo Cassette: A Microfluidic Microgravity Microbial System For Synthetic Biology Unit Tests and Satellite Missions

Although methods in the design-build-test life cycle of the synthetic biology field have grown rapidly, the expansion has been non-uniform. The design and build stages in development have seen innovations in the form of biological CAD and more efficient means for building DNA, RNA, and other biological constructs. The testing phase of the cycle remains in need of innovation. Presented will be both a theoretical abstraction of biological measurement and a practical demonstration of a microfluidics-based platform for characterizing synthetic biological phenomena. Such a platform demonstrates a design of additive manufacturing (3D printing) for construction of a microbial fuel cell (MFC) to be used in experiments carried out in space. First, the biocompatibility of the polypropylene chassis will be demonstrated. The novel MFCs will be cheaper, and faster to make and iterate through designs. The novel design will contain a manifold switchingdistribution system and an integrated in-chip set of reagent reservoirs fabricated via 3D printing. The automated nature of the 3D printing yields itself to higher resolution switching valves and leads to smaller sized payloads, lower cost, reduced power and a standardized platform for synthetic biology unit tests on Earth and in space. It will be demonstrated that the application of unit testing in synthetic biology will lead to the automatic construction and validation of desired constructs. Unit testing methodologies offer benefits of preemptive problem identification, change of facility, simplicity of integration, ease of documentation, and separation of interface from implementation, and automated design

Bacteria photosensitized by intracellular gold nanoclusters for solar fuel production.

The demand for renewable and sustainable fuel has prompted the rapid development of advanced nanotechnologies to effectively harness solar power. The construction of photosynthetic biohybrid systems (PBSs) aims to link preassembled biosynthetic pathways with inorganic light absorbers. This strategy inherits both the high light-harvesting efficiency of solid-state semiconductors and the superior catalytic performance of whole-cell microorganisms. Here, we introduce an intracellular, biocompatible light absorber, in the form of gold nanoclusters (AuNCs), to circumvent the sluggish kinetics of electron transfer for existing PBSs. Translocation of these AuNCs into non-photosynthetic bacteria enables photosynthesis of acetic acid from CO2. The AuNCs also serve as inhibitors of reactive oxygen species (ROS) to maintain high bacterium viability. With the dual advantages of light absorption and biocompatibility, this new generation of PBS can efficiently harvest sunlight and transfer photogenerated electrons to cellular metabolism, realizing CO2 fixation continuously over several days

In silico characterization of microbial electrosynthesis for metabolic engineering of biochemicals

<p>Abstract</p> <p>Background</p> <p>A critical concern in metabolic engineering is the need to balance the demand and supply of redox intermediates such as NADH. Bioelectrochemical techniques offer a novel and promising method to alleviate redox imbalances during the synthesis of biochemicals and biofuels. Broadly, these techniques reduce intracellular NAD⁺to NADH and therefore manipulate the cell's redox balance. The cellular response to such redox changes and the additional reducing power available to the cell can be harnessed to produce desired metabolites. In the context of microbial fermentation, these bioelectrochemical techniques can be used to improve product yields and/or productivity.</p> <p>Results</p> <p>We have developed a method to characterize the role of bioelectrosynthesis in chemical production using the genome-scale metabolic model of <it>E. coli</it>. The results in this paper elucidate the role of bioelectrosynthesis and its impact on biomass growth, cellular ATP yields and biochemical production. The results also suggest that strain design strategies can change for fermentation processes that employ microbial electrosynthesis and suggest that dynamic operating strategies lead to maximizing productivity.</p> <p>Conclusions</p> <p>The results in this paper provide a systematic understanding of the benefits and limitations of bioelectrochemical techniques for biochemical production and highlight how electrical enhancement can impact cellular metabolism and biochemical production.</p

Méthodologie d'éconconception pour un procédé innovant: la bioélétrosynthèse des déchets organiques

International audienceBulk chemicals and liquid fuels are currently produced almost exclusively from petrochemical feedstock. In the light of emission reduction targets and the dependence on non renewable resources, the production of the same or functionally equivalent chemicals from renewable resources may play an important role [1, 2]. The project BIORARE (Bioelectrosynthesis for the refinery of residual waste) was set up to contribute to this objective. Its purpose is to use microbial electrosynthesis for the direct production of fuels and chemicals from organic waste and CO2 (see figure 1). Ecoconception is used to help to make choices. This is this work which is study.In a first step, we had to determine which parameters of the Bioelectrosynthesis (BES) could be the most impacting ones to define the priorities to be considered to minimize the potential impacts of the entire process. Some flows could be sensitive: the nature and the quantity of outputs, the nature and the quantity of materials, and the amount of energy used. The inventory of these flows had to be the first step. Thanks to databases and literature four have been identified as sensitive: electrodes, membrane, energy and chemicals produced.After determining this, we have to design the model for coupling anaerobic digestion to the BES. This was realized using Life Cycle Assessment approach. The goal of this assessment is to determine the relative influence of various target parameters on the impacts of the process. For example, results will allow assessing if the choice of a material for the electrode could have a significant influence on total impacts. Our methodology illustrates to what extend Life Cycle Assessment could help for the conception of a process, through the evaluation of the contribution of various parameters to the impacts. After, it is possible to integrate them into a model to determine what impacts they could have on the whole production chemicals or fuels from organic waste system.ACV de production de bioéthanol par bioélectrosynthèse de déchets organiques

Microbial electrochemical reactors based on fluid-like electrodes: a new biotech platform for performing environmental applications

La crisis climática en la que se encuentra el planeta nos está llevando a buscar soluciones y alternativas para producir el menor impacto en la naturaleza. Las emisiones de CO2 han aumentado un 40 % desde la revolución industrial. Las medidas para reducir estas emisiones implican un cambio en muchos de nuestros hábitos diarios como de consumo. La demanda energética en nuestra vida cotidiana es uno de los factores que incrementan estas emisiones. Los reactores electroquímico-microbianos de lecho fluidizado son una tecnología muy versátil y flexible que pueden hacer frente a estos problemas ambientales. Su funcionamiento se basa en la interacción de las bacterias electroactivas con materiales conductores insolubles. En esta tesis se han estudiado dos procesos distintos del lecho fluidizado: como donador de electrones para reducir otros compuestos y como aceptor final de electrones. La operación del sistema como donador de electrones consistió en la utilización del electrodo fluidizado como fuente de energía para la reducción de compuestos a través del metabolismo de microorganismos electroactivos (capítulos 2 y 3). El último capítulo de experimentación se basó en la mejora del material utilizado en previos lechos fluidizados, con el objeto de mejorar la interacción con microorganismos electroactivos operando en continuo y polarizando el lecho fluidizado como ánodo (capítulo 4). Esta tesis se divide en 5 capítulos. En el capítulo 1 se describe el estado de arte de las tecnologías electroquímicas microbianas, centrándose en los reactores electroquímicos microbianos de lecho fluidizado (ME-FBR), así como los problemas ambientales que pueden abordarse con ellas. Los siguientes capítulos son experimentales (2, 3 y 4). En el capítulo 5 se establece una discusión general y una serie de conclusiones tras el periodo de investigación. Así, en el capítulo 2, se recurrió a un ME-FBR para la selección de microorganismos autótrofos capaces de interaccionar con un lecho fluidizado polarizado a -0.6, -0.8 y a -1 V (vs. Ag/AgCl). Este biocátodo fluidizado permitió actuar como donador de electrones directo o mediado por H2, para la fijación microbiana de CO2. La detección de ácidos volátiles y el aumento de biomasa, demostró que la fijación bioelectroquímica de CO2 es factible en este tipo de reactores. En el capítulo 3, se desarrolló un estudio comparativo entre un biofiltro de lecho fijo electroconductor y uno fluidizado para la reducción bioelectroquímica autotrófica de nitrato. Los ensayos se realizaron tanto a circuito abierto como a un potencial de polarización de -0.3 V (vs. Ag/AgCl), para garantizar la no producción de hidrógeno. El estudio demostró la desnitrificación bioelectroquímica en ambos tipos de reactores operando tanto en fed-batch como en continuo.Las limitaciones del cultivo continuo de microorganismos mostraron limitaciones en electrodos fluidizados. Además, se estableció una propuesta sobre las relaciones de sintropía entre las distintas comunidades microbianas analizadas. En el capítulo 4 se aborda las limitaciones del cultivo continuo de microorganismos electroactivos planctónicos con electrodos fluidizados de carbón vitreo detectados en el capítulo 3. La pérdida de las células por la operación en continuo sugería establecer cambios en el material que favorecieran la colonización de este. En este sentido se modificó químicamente la superficie del carbón vítreo añadiendo grupos oxigenados. Estos grupos facilitaron la adhesión de las células sobre la superficie a través de la conocida interacción entre grupos carboxilo y citocromos C, presentes en la membrana externa de Geobacter sulfurreducens. El nuevo material funcionalizado se utilizó como ánodo fluidizado permitiendo el cultivo de Geobacter en continúo, utilizando acetato como donador de electrones y fuente de carbono. Los análisis de microscopia SEM y confocal demostraron la eficiente colonización del material funcionalizado frente a la deficiente operación del material original. Para finalizar esta tesis, el capítulo 5 aporta una discusión general en formato pregunta-respuesta y detalla las conclusiones obtenidas a partir de la investigación