CONICET | Buscador de Institutos y Recursos Humanos

In this work, we explore the capacity of an autochthonous strain of Rhodopseudomonas palustris, (AZUL strain) to grow in continuous culture electrochemical bioreactors interacting with an electrode. A phylogenetic analysis based on the 23S rDNA gene indicated that AZUL is phylogenetically closest to CGA009, TIE-1 and DX-1. The latter two strains have been previously reported to interact with an electrode. R. palustris AZUL was capable of growing in bioreactors, forming biofilms on graphite electrodes under photoheterotrophic conditions. Electrochemical assays showed that the biofilms formed on electrodes under various applied potentials (polarized) had specific redox signals that varied with light, polarization time and potential value. Despite these signals, the current obtained from biofilms in chronoamperometric assays did not overcome 9.5µA/cm2. Moreover, we could not see any relationship between current magnitude and biomass accumulation on the electrode. At least two well defined redox pairs centered at 0,4 and 0,6V (Ag/AgCl- 3M NaCl) were detected whose amplitudes depended on the imposed conditions. In addition, SEM images revealed differences in the structure of biofilms grown on polarized and non-polarized control electrodes. These results indicate that R. palustris AZUL cells possess extracellular electron transfer mechanisms that do not seem to be directly related to cellular respiration, but most probably to a mechanism of protection against oxidative stress. Due to its ease of culture in laboratory and its extraordinary metabolic versatility, the study of the optimal conditions in which this bacterium exchanges electrons with a polarized electrode in a bioelectrochemical system deserves to be extended aiming at developing technological applications.