POSSIBLE ELECTRON UPTAKE MECHANISMS OF ELECTROAUTOTROPHIC NITRATE REDUCING BACTERIA

RODRIGUEZ SIMÓN, CARLOS NORBERTO; BUSALMEN, JUAN PABLO; BONANNI, SEBASTIAN; VILLARREAL, FERNANDO

Congreso; XVI CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2021

Samige/Saib

Nitrate generates adverse health effects and is responsible for the eutrophication of surface water. Its removal from contaminated waters can be achieved by denitrification, which consists on 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 and wastewater 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 attention in 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 in the 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 mechanism of electroautotrophic nitrate reducing bacteria (nrb) was studied by means of bioinformatic tools. For this purpose, 14 nitrate reducing bacteria (nrb) with sequenced genome were selected and separated according to whether they have proven electroactivity (capacity of using a cathode as electron donor) or not. Using the Psort and Phobius tools, proteins that could serve as a connection with the extracellular space were identified and classified according to their localization (excreted, outer membrane, periplasm or inner membrane and connected to the periplasm). Among them, those capable of transporting electrons (cytochromes, pseudoazurin, among others) were selected using Prosite, a trustworthy motif finder. For each microorganism, an interaction network for these proteins was generated through STRING, a database with information on protein-protein interaction (based on homology and experimental data, among other parameter) from more than 14000 genomes. The interaction between proteins in the nrb electroactive microorganisms revealed the existence of two common pathways that could connect the extracellular space with cytochromes involved in denitrification and on the electron transport chain. We generated a predictor tool consisting on training dataset generated from proteobacteria proteomes. We retrieved sequences with hmmer profiles for cytochrome C1 and D1 superfamilies (Pfam), and used them to reconstruct the corresponding 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 genomic information.