Forming electrochemically active biofilms from garden compost under chronoamperometry

Dimensionally stable anodes (DSA) were polarized at different constant potential values for several days in garden compost. After an initial lag period ranging from 1 to 10.5 days, the current increased fast and then stabilized for days. Current densities higher than 100 mA m2 and up to 385 mA m2 were obtained with the sole organic matter contained in compost as substrate. Control experiments performed with sterilized compost, oscillations of the current with the temperature, kinetics of the exponential phase of current increase and observations of the surface of electrodes by epifluorescence microscopy showed that the current was controlled by the colonization of the electrode surface by a biofilm which originated the indigenous flora of compost. Three individually addressed electrodes polarized at different potentials in the same reactor led to identical current evolutions on each electrode, which underlined the key role of the microbial flora of the compost in the discrepancy observed in the other experiments. Chronoamperometry revealed a promising technique to check natural environments for new electrochemically active microbial species

Acetate to enhance electrochemical activity of biofilms from garden compost

Dimensionally Stable Anodes embedded in garden compost and maintained under constant polarization at 0.50 V/SCE for several days progressively became covered by a microbial biofilm that gave them the capability to oxidize the organic matter contained in the compost. The effect of acetate supply on the electrochemical activity of biofilms was investigated either by adding acetate after biofilm formation or mixing it into the compost initially. Addition of acetate allowed the current density values to increase up to 545 mA/m2. Six individually monitored electrodes set up in the same reactor showed very good reproducibility, indicating that discrepancies observed between the different experiments were mainly due the different batches of compost. A numerical treatment of the epifluorescent microscopy pictures allowed the biofilm coverage ratios to be assessed. Comparing the variations of current density during chronoamperometry with the biofilm surface coverage ratios and with the current obtained by cyclic voltammetry led us to propose a mechanism based on two different steps that corresponded to different time-scales: slow acetate oxidation through the cell metabolism and fast electron transfer between the cell and the electrode surface

Catalysis of the electrochemical reduction of oxygen by bacteria isolated from electro-active biofilms formed in seawater

Biofilmsformed in aerobic seawater on stainless steel are known to be efficient catalysts of the electrochemicalreduction of oxygen. Based on their genomic analysis, seven bacterial isolates were selected and a cyclic voltammetry (CV) procedure was implemented to check their electrocatalytic activity towards oxygenreduction. All isolates exhibited close catalytic characteristics. Comparison between CVs recorded with glassy carbon and pyrolytic graphite electrodes showed that the catalytic effect was not correlated with the surface area covered by the cells. The low catalytic effect obtained with filtered isolates indicated the involvement of released redox compounds, which was confirmed by CVs performed with adsorbed iron–porphyrin. None of the isolates were able to form electro-activebiofilms under constant polarization. The capacity to catalyze oxygenreduction is shown to be a widespread property among bacteria, but the property detected by CV does not necessarily confer the ability to achieve stable oxygenreduction under constant polarization

Biofilms éléctroactifs : formation, caractérisation et mécanismes

Certaines bactéries, capables d'échanger des électrons avec un matériau conducteur sans l'aide de médiateur, forment sur la surface conductrice des biofilms électroactifs. Cette propriété bactérienne a été récemment découverte (2001). Les objectifs de ce travail sont de développer des biofilms électroactifs dans divers environnements naturels à partir de la flore indigène, puis par des méthodes électrochimiques complémentaires, chronoampérométrie et voltammétrie cyclique, d'évaluer l'électroactivité d'isolats issus de biofilms ainsi formés et de caractériser les mécanismes du transfert d'électrons entre bactéries et matériau. Tout d'abord, des biofilms électroactifs ont été développés en chronoampérométrie dans du terreau et de l'eau provenant de la mangrove guyanaise. Ces biofilms sont respectivement capables d'utiliser une électrode comme accepteur d'électrons (oxydation) ou comme donneur (réduction). Dans le terreau, les résultats obtenus en chronoampérométrie et en voltammétrie cyclique suggèrent un transfert électronique en deux étapes : consommation lente du substrat puis transfert rapide des électrons entre les bactéries et l'électrode.Ensuite, la capacité à catalyser la réduction de l'oxygène a été démontrée par voltammétrie cyclique pour des isolats aérobies facultatifs issus des biofilms du terreau (Enterobacter spp. et Pseudomonas spp.) et des isolats aérobies obtenus à partir de biofilms marins (majoritairement Roseobacter spp.). Enfin, des biofilms générant une augmentation du courant en chronoampérométrie ont été développés en bioréacteur sur milieu synthétique à partir d'une culture pure d'isolats. Ainsi, pour la première fois, l'électroactivité de plusieurs souches anaérobies de Geobacter bremensis isolées des biofilms du terreau a été mise en évidence. ABSTRACT : Some bacteria, which are able to exchange electrons with a conductive material without mediator form on conductive surfaces electroactive biofilms. This bacterial property has been recently discovered (2001). Objectives of this work are to develop electroactive biofilms in various natural environments from indigenous flora, then through complementary electrochemical techniques (chronoamperometry and cyclic voltammetry), to evaluate electroactivity of isolates coming from so-formed biofilms and to characterize mechanisms of electron transfer between bacteria and materials. First, electroactive biofilms have been developed under chronoamperometry in garden compost and in water coming from Guyana mangrove. These biofilms were respectively able to use an electrode as electron acceptor (oxidation) or as electron donor (reduction). In compost, results obtained in chronoamperometry and cyclic voltammetry suggest a two-step electron transfer: slow substrate consumption, then rapid electron transfer between bacteria and the electrode. Thereafter, the ability to reduce oxygen was demonstrated with cyclic voltammetry for facultative aerobic isolates from compost biofilms (Enterobacter spp. and Pseudomonas spp.) and for aerobic isolates obtained from marine electroactive biofilms (Roseobacter spp. in majority). Finally, biofilms inducing current increase in chronoamperometry were developed in bioreactor with synthetic medium from a pure culture of isolates. Hence, for the first time, electroactivity of several anaerobic strains of Geobacter bremensis isolated from compost biofilms was highlighte

Electroactive biofilms: new means for electrochemistry

This work demonstrates that electrochemical reactions can be catalysed by the natural biofilms that form on electrode surfaces dipping into drinking water or compost. In drinking water, oxygen reduction was monitored with stainless steel ultra-microelectrodes under constant potential electrolysis at )0.30 V/SCE for 13 days. 16 independent experiments were conducted in drinking water, either pure or with the addition of acetate or dextrose. In most cases, the current increased and reached 1.5–9.5 times the initial current. The current increase was attributed to biofilm forming on the electrode in a similar way to that has been observed in seawater. Epifluorescence microscopy showed that the bacteria size and the biofilm morphology depended on the nutrients added, but no quantitative correlation between biofilm morphology and current was established. In compost, the oxidation process was investigated using a titanium based electrode under constant polarisation in the range 0.10–0.70 V/SCE. It was demonstrated that the indigenous micro-organisms were responsible for the current increase observed after a few days, up to 60 mA m)2. Adding 10 mM acetate to the compost amplified the current density to 145 mA m)2 at 0.50 V/SCE. The study suggests that many natural environments, other than marine sediments, waste waters and seawaters that have been predominantly investigated until now, may be able to produce electrochemically active biofilm

Harvesting Electricity with Geobacter bremensis Isolated from Compost

Electrochemically active (EA) biofilms were formed on metallic dimensionally stable anode-type electrode (DSA), embedded in garden compost and polarized at +0.50 V/SCE. Analysis of 16S rRNA gene libraries revealed that biofilms were heavily enriched in Deltaproteobacteria in comparison to control biofilms formed on non-polarized electrodes, which were preferentially composed of Gammaproteobacteria and Firmicutes. Among Deltaproteobacteria, sequences affiliated with Pelobacter and Geobacter genera were identified. A bacterial consortium was cultivated, in which 25 isolates were identified as Geobacter bremensis. Pure cultures of 4 different G. bremensis isolates gave higher current densities (1400 mA/m2 on DSA, 2490 mA/m2 on graphite) than the original multi-species biofilms (in average 300 mA/m2 on DSA) and the G. bremensis DSM type strain (100–300 A/m2 on DSA; 2485 mA/m2 on graphite). FISH analysis confirmed that G. bremensis represented a minor fraction in the original EA biofilm, in which species related to Pelobacter genus were predominant. The Pelobacter type strain did not show EA capacity, which can explain the lower performance of the multi-species biofilms. These results stressed the great interest of extracting and culturing pure EA strains from wild EA biofilms to improve the current density provided by microbial anodes

Biofilms éléctroactifs (formation, caractérisation et mécanismes)

Certaines bactéries, capables d'échanger des électrons avec un matériau conducteur sans l'aide de médiateur, forment sur la surface conductrice des biofilms électroactifs. Cette propriété bactérienne a été récemment découverte (2001). Les objectifs de ce travail sont de développer des biofilms électroactifs dans divers environnements naturels à partir de la flore indigène, puis par des méthodes électrochimiques complémentaires, chronoampérométrie et voltammétrie cyclique, d'évaluer l'électroactivité d'isolats issus de biofilms ainsi formés et de caractériser les mécanismes du transfert d'électrons entre bactéries et matériau. Tout d'abord, des biofilms électroactifs ont été développés en chronoampérométrie dans du terreau et de l'eau provenant de la mangrove guyanaise. Ces biofilms sont respectivement capables d'utiliser une électrode comme accepteur d'électrons (oxydation) ou comme donneur (réduction). Dans le terreau, les résultats obtenus en chronoampérométrie et en voltammétrie cyclique suggèrent un transfert électronique en deux étapes : consommation lente du substrat puis transfert rapide des électrons entre les bactéries et l'électrode.Ensuite, la capacité à catalyser la réduction de l'oxygène a été démontrée par voltammétrie cyclique pour des isolats aérobies facultatifs issus des biofilms du terreau (Enterobacter spp. et Pseudomonas spp.) et des isolats aérobies obtenus à partir de biofilms marins (majoritairement Roseobacter spp.). Enfin, des biofilms générant une augmentation du courant en chronoampérométrie ont été développés en bioréacteur sur milieu synthétique à partir d'une culture pure d'isolats. Ainsi, pour la première fois, l'électroactivité de plusieurs souches anaérobies de Geobacter bremensis isolées des biofilms du terreau a été mise en évidence.Some bacteria, which are able to exchange electrons with a conductive material without mediator form on conductive surfaces electroactive biofilms. This bacterial property has been recently discovered (2001). Objectives of this work are to develop electroactive biofilms in various natural environments from indigenous flora, then through complementary electrochemical techniques (chronoamperometry and cyclic voltammetry), to evaluate electroactivity of isolates coming from so-formed biofilms and to characterize mechanisms of electron transfer between bacteria and materials. First, electroactive biofilms have been developed under chronoamperometry in garden compost and in water coming from Guyana mangrove. These biofilms were respectively able to use an electrode as electron acceptor (oxidation) or as electron donor (reduction). In compost, results obtained in chronoamperometry and cyclic voltammetry suggest a two-step electron transfer: slow substrate consumption, then rapid electron transfer between bacteria and the electrode. Thereafter, the ability to reduce oxygen was demonstrated with cyclic voltammetry for facultative aerobic isolates from compost biofilms (Enterobacter spp. and Pseudomonas spp.) and for aerobic isolates obtained from marine electroactive biofilms (Roseobacter spp. in majority). Finally, biofilms inducing current increase in chronoamperometry were developed in bioreactor with synthetic medium from a pure culture of isolates. Hence, for the first time, electroactivity of several anaerobic strains of Geobacter bremensis isolated from compost biofilms was highlighted.TOULOUSE-ENSIACET (315552325) / SudocSudocFranceF

Identification of bacterial populations forming EAB.

<p><i>rrs</i> based identification of clones from polarised and non polarised DSA clone libraries.</p

Impact of electrodes polarisation on bacterial community structure.

<p>Comparison of genetic fingerprints of compost EAB obtained on polarized (PE) and non-polarized (NPE) DSA by DGGE.</p

Phyloenetic and electrochemical activity of <i>G. bremensis</i> isolates.

<p>Phyloenetic tree based on <i>rrs</i> gene sequence (A) and chronoamerometry (B) of <i>G. bremensis</i> isolates and type strain DSM 12179.</p