POSSIBLE ELECTRON UPTAKE MECHANISMS OF ELECTROAUTOTROPHIC NITRATE REDUCING BACTERIA/ POSIBLES MECANISMOS DE TOMA DE ELECTRONES PARA BACTERIAS REDUCTORAS DE NITRATO ELECTROAUTOTRÓFICAS

RODRÍGUEZ SIMÓN, CARLOS NORBERTO; BUSALMEN, JUAN PABLO; BONANNI, PABLO SEBASTIAN; VILLAREAL, FERNANDO

Congreso; SAIB-SAMIGE 2021; 2023

Nitrate generates adverse health effects and is responsible for the eutrophication of surface water. Its removal fromcontaminated waters can be achieved by denitrification, which consists of the biological reduction of nitrate to dinitrogen gas.Denitrifying bacteria are often outcompeted by aerobic bacteria in the use of carbon and electron sources during water andwastewater treatment. Consequently, the availability of carbon and electron sources is a limiting factor for denitrification.Electroautotrophs are microorganisms that use a polarized electrode (cathode) as sole electron donor for energy generation,CO2 fixation and other metabolic reactions. The use of a cathode as electron source for denitrifiers has received great attentionin recent years as it allows to surpass the mentioned limitations that arise in wastewater treatment processes. Unfortunately,the applicability of this concept is limited by the low current densities produced by the microorganisms. Proteins involved inthe electron uptake from the cathode (which is in the extracellular space) are still not identified, mainly due to difficulties in its purification determined by the low biomass obtained on the systems. In the present work, the electron uptake mechanismof electroautotrophic nitrate reducing bacteria (nrb) was studied by means of bioinformatic tools. For this purpose, 14 nitratereducing bacteria (nrb) with sequenced genome were selected and separated according to whether they have provenelectroactivity (capacity of using a cathode as electron donor) or not. Using the Psort and Phobius tools, proteins that couldserve as a connection with the extracellular space were identified and classified according to their localization (excreted, outermembrane, periplasm or inner membrane and connected to the periplasm). Among them, those capable of transportingelectrons (cytochromes, pseudoazurin, among others) were selected using Prosite, a trustworthy motif finder. For eachmicroorganism, an interaction network for these proteins was generated through STRING, a database with information onprotein-protein interaction (based on homology and experimental data, among other parameter) from more than 14000genomes. The interaction between proteins in the nrb electroactive microorganisms revealed the existence of two commonpathways that could connect the extracellular space with cytochromes involved in denitrification and on the electron transportchain. We generated a predictor tool consisting of training dataset generated from proteobacteria proteomes. We retrievedsequences with hmmer profiles for cytochrome C1 and D1 superfamilies (Pfam) and used them to reconstruct thecorresponding phylogenies. Finally, we used HMMERCTTER clustering module to identify groups autodetected with 100%precision and recall. In this way, putative uncultured electroautotrophic denitrifiers could be identified from their genomicinformation.