Possible electron uptake mechanisms of electroautotrophic nitrate reducing bacteria.

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

Congreso; Congreso virtual conjunto SAIB-SAMIGE 2021; 2021

SAMIGE

´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 ofcarbon and electron sources during water and wastewater treatment.Consequently, the availability of carbon and electron sources is a limitingfactor for denitrification. Electroautotrophs are microorganisms that use a polarized electrode (cathode)as sole electron donor for energy generation, CO2 fixation and other metabolicreactions. The use of a cathode as electron source for denitrifiers hasreceived great attention in recent years as it allows to surpass the mentionedlimitations that arise in wastewater treatment processes. Unfortunately theapplicability of this concept is limited by the low current densities producedby the microorganisms. Proteins involved in the electron uptake from thecathode (which is in the extracellular space) are still not identified, mainlydue to difficulties in its purification determined by the low biomass obtainedon the systems. In the present work, the electron uptake mechanism ofeletroautotrophic nitrate reducing bacteria was studied by means ofbioinformatic tools. For this purpose, nrb with a sequenced genome wereselected and separated according to whether they have proven electroactivity(capacity of using a cathode as electron donor) or not. Using the psort andphobius tools,proteins that could serve as a connection with the extracellularspace were identified and classified according to its localization (excreted,outermembrane, periplasm or inner membrane and connected to the periplasm).Between them, those capable of transporting electrons (cytochromes,pseudoazurin, among others) were selected with the help of the prosite tool, atrustworthy motif finder,. For each microorganism, an interaction network forthese proteins was generated through string, a program withmore than 14000 genomes which allows predicting interactions over selectedproteins, based on homology and experimental data, among other parameters. Theinteraction between proteins in the nrb electroactivemicroorganisms revealed the existence of two common pathways that could connectthe extracellular space with cytochromes involved in denitrification and on theelectron transport chain. A predictor was obtainedwith the hmmer tool, a program taht uses hidden Markov models and is capable ofmaking reliable motif from a set of proteins, followed to its evaluation usingthe group phylogeny. In this way, putative uncultured electroautotrophic denitrifierscould be identified from genomic information´.