Bioelectrochemical systems: a new approach towards environmental and industrial biotechnology

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New methods to study anaerobic microbial metabolism

Microbial electrosynthesis (MES) is an emerging technology aimed at converting excess electrical energy into storable biofuels or chemical precursors. The technology relies on the anaerobic microbial conversion of CO2 or organics into desired products, like CO2 to acetate by homoacetogens.The objective of this work is to develop techniques for screening microorganisms and understand how desired products will inhibit or stimulate growth of the microorganism and/or the conversion of the substrate into the desired product. The developed techniques are not limited to MES but can be applied to other anaerobic microbial conversions such as in anaerobic digestion or in the colon. Model organisms used in this work are Acetobacterium woodii and Clostridium ljungdahlii for MES. Faecalibacterium prausnitzii was uses as the colon model.To assess inhibition by products under growing conditions, continuous anaerobic incubations were performed using 96 well plates in microplate readers. Substrate turnover under non-growing conditions was assessed by using riboflavin (RF) reduction as an electrochemical probe. RF reduction was measured with a rotating disk electrode. The same experiments, under non-growing conditions, were also performed spectophotometrically. The obtained RF reduction rates could be recalculated into a substrate conversion rate per microorganism for both the RDE and spectrophotometric data.The developed methods were useful in determining product inhibitions under growing and non-growing conditions. For example: (i) anaerobic growth of the organisms was highly similar in hungate tubes compared to well plate incubations and (ii) riboflavin turnover by F. prausnitzii as determined electrochemically as well as spectrophotometrically yielded similar rates.Microbial electrosynthesis (MES) is an emerging technology aimed at converting excess electrical energy into storable biofuels or chemical precursors. The technology relies on the anaerobic microbial conversion of CO2 or organics into desired products, like CO2 to acetate by homoacetogens.The objective of this work is to develop techniques for screening microorganisms and understand how desired products will inhibit or stimulate growth of the microorganism and/or the conversion of the substrate into the desired product. The developed techniques are not limited to MES but can be applied to other anaerobic microbial conversions such as in anaerobic digestion or in the colon. Model organisms used in this work are Acetobacterium woodii and Clostridium ljungdahlii for MES. Faecalibacterium prausnitzii was uses as the colon model.To assess inhibition by products under growing conditions, continuous anaerobic incubations were performed using 96 well plates in microplate readers. Substrate turnover under non-growing conditions was assessed by using riboflavin (RF) reduction as an electrochemical probe. RF reduction was measured with a rotating disk electrode. The same experiments, under non-growing conditions, were also performed spectophotometrically. The obtained RF reduction rates could be recalculated into a substrate conversion rate per microorganism for both the RDE and spectrophotometric data.The developed methods were useful in determining product inhibitions under growing and non-growing conditions. For example: (i) anaerobic growth of the organisms was highly similar in hungate tubes compared to well plate incubations and (ii) riboflavin turnover by F. prausnitzii as determined electrochemically as well as spectrophotometrically yielded similar rates.C