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

FRITTAYON C.; GONZALEZ BLOTTA L.; ORDÓÑEZ, M.V.; SCHROTT GD

Congreso; CONGRESO CONJUNTO SAIB-SAMIGE 2021; 2021

Asociación Civil de Microbiología General (SAMIGE) - Sociedad Argentina de Bioquímica y Biología Molecular (SAIB)

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 proved E. coli can ferment glycerol to bioethanol and H2, in an anaerobically and pH dependent manner. Also, it has been shown that hydrogen accumulation in the culture inhibits further glycerol consumption and ethanol yields. In order to avoid this inhibitory effect, 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 a polarized electrode. Looking forward to creating a bio-electrochemical system capable of reducing the inhibitory effect of H2 accumulation over glycerol fermentation, we propose to couple E. coli fermentative metabolism to G. sulfurreducens electroactivity. In this work we present the first steps towards obtaining optimal condition where these bacteria can grow together. Typically, G. sulfurreducens is cultivated at 28-30 ºC while E. coli grows optimally at 37 ºC. Then, it was necessary to evaluate and characterize G. sulfurreducens growth and electrochemical response at 37 ºC. For this, we grew Geobacter biofilms anaerobically, in a three-electrode electrochemical cell, with graphite rods (i.e. working electrode) as unique electron acceptor, sodium acetate as carbon and electron source, platinum wire as counter electrode and Ag/AgCl NaCl 3M as reference electrode. The working electrode was polarized at 0.2 V vs reference, and current output (i.e. bacteria respiration) measured along time. N2/CO2 gas was continuously bubbled into the media to complete bicarbonate buffer and avoid O2 diffusing into the cell. Initially growth temperature was kept at 30 ºC until fully developed biofilms were obtained and cyclic voltammetry and open circuit potential (OCP) measurement were performed to typify the electrochemical response. Then, temperature was shifted to 37 ºC and current evolutions as well as electrochemical assays as described above were performed. In addition, new biofilms were developed directly at 37 ºC from bacteria previously adapted to this temperature. Results obtained show similar maximal 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, OCP curves 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 electroactivity performance point of view, when selecting the best culturing condition for consortia with E. coli.