GROWTH AND ELECTROCHEMICAL CHARACTERIZATION OF Geobacter sulfurreducens BIOFILMS DEVELOPED AT HIGHER TEMPERATURE THAN TYPICAL

FRITTAYON CATALINA; GONZALES BLOTTA LUCÍA; ORDOÑEZ MARÍA VICTORIA; SCHROTT GERMÁN DAVID

Congreso; SAIB-SAMIGE 2021; 2021

Since 2012 worldwide biodiesel production has increased constantly. However, biodiesel industries generate glycerol as by-product in such quantities that it has become a burden to biorefineries. Interestingly, in the last decade several studies provedE. coli can ferment glycerol to bioethanol and H2, in an anaerobically and pH dependent manner. Also, it has been shown thathydrogen accumulation in the culture inhibits further glycerol consumption and ethanol yields. In order to avoid this inhibitoryeffect, H2 is usually removed by bubbling a noble gas. On the other hand, Geobacter sulfurreducens, the most studied electro-active (i.e. electric current producing) bacteria, has the ability to oxidize H2 and may transfer the obtained electrons to apolarized electrode. Looking forward to creating a bio-electrochemical system capable of reducing the inhibitory effect of H2accumulation over glycerol fermentation, we propose to couple E. coli fermentative metabolism to G. sulfurreducenselectroactivity. In this work we present the first steps towards obtaining optimal condition where these bacteria can growtogether. Typically, G. sulfurreducens is cultivated at 28-30 ºC while E. coli grows optimally at 37 ºC. Then, it was necessaryto evaluate and characterize G. sulfurreducens growth and electrochemical response at 37 ºC. For this, we grew Geobacterbiofilms anaerobically, in a three-electrode electrochemical cell, with graphite rods (i.e. working electrode) as unique electronacceptor, sodium acetate as carbon and electron source, platinum wire as counter electrode and Ag/AgCl NaCl 3M as referenceelectrode. The working electrode was polarized at 0.2 V vs reference, and current output (i.e. bacteria respiration) measuredalong time. N2/CO2 gas was continuously bubbled into the media to complete bicarbonate buffer and avoid O2 diffusing intothe cell. Initially growth temperature was kept at 30 ºC until fully developed biofilms were obtained and cyclic voltammetryand open circuit potential (OCP) measurement were performed to typify the electrochemical response. Then, temperature wasshifted to 37 ºC and current evolutions as well as electrochemical assays as described above were performed. In addition, newbiofilms were developed directly at 37 ºC from bacteria previously adapted to this temperature. Results obtained show similarmaximal currents at both temperatures while no significant change in the voltammetry response was observed at 37ºC,suggesting no changes in the rate limiting steps on the electron pathway from cells interior to the electrode. Moreover, OCPcurves depicted the same trend for all conditions, further supporting no significant changes in the electron pathways of G.sulfurreducens. These results show that cultivating G. sulfurreducens at 37 ºC should not be a problem, from an electroactivityperformance point of view, when selecting the best culturing condition for consortia with E. coli.