Electrochemical enrichment of haloalkaliphilic nitrate-reducing microbial biofilm at the cathode of bioelectrochemical systems

Abstract

Summary Electrotrophic microorganisms have not been well studied in extreme environments. Here, we report on the nitrate-reducing cathodic microbial biofilm from a haloalkaline environment. The biofilm enriched via electrochemical approach under 9.5 pH and 20 g NaCl/L salinity conditions achieved current density and nitrate reduction efficiency via partial and complete denitrification. Voltammetric characterization of the biocathodes revealed a redox center with 0.294 0.003 ( vs. Ag/AgCl) formal potential putatively involved in the electron uptake process. The lack of soluble redox mediators and hydrogen-driven nitrate reduction suggests direct-contact cathodic electron uptake by the nitrate-reducing microorganisms in the enriched biofilm. 16S-rRNA amplicon sequencing of the cathodic biofilm revealed the presence of unreported Pseudomonas, Natronococcus, and Pseudoalteromonas spp. at , and relative sequence abundances, respectively. The enriched nitrate-reducing microorganisms also reduced nitrate efficiently using soluble electron donors found in the lake sediments, thereby suggesting their role in N-cycling in such environments.

Protocol for bioelectrochemical enrichment, cultivation, and characterization of extreme electroactive microorganisms

“… ∗∗∗ Note: All the instruments mentioned above can be of any reliable make. Procedure: The medium composition is presented in Table 1 ( Yadav and Patil, 2020 ; Chaudhary et al., 2021 ). Dissolve the components in 500 mL distilled water, and then make the final volume to 1000 mL.…”

“… Specific/selected environment site (e.g., subsurface sediments from aquatic environments, anaerobic sludge, etc.) N/A Deposited data Raw data Chaudhary et al. (2021) NCBI-SRA: SRR12506991 Software and algorithms EC Lab BioLogic Science Instruments, France N/A Other 500 Watt ultrasonic processor VC 505 Sonics https://www.sonics.com/liquid-processing/products/vibra-cell-processors/vc-505-vc-750/ Ag/AgCl (3.5 M KCl) electrode BioLogic Science Instruments, France Cat#RE-1B Amber-colored bottles (Wide mouth HDPE) Tarsons Cat#581350 Autoclave, CL-32L ALP Co. Ltd. http://alpco.co.jp/en/auto Biosafety cabinet, Logic+ A2 Labconco Corporation https://www.labconco.com/category/biological-safety-cabinets-enclosures Conductive Cement Alfa Aesar Cat#AA41212-15 Conductivity meter, Oakton 2700 Oakton http://www.4oakton.com/proddetail.asp?parent=53&prod=371&TotRec=5 Customized Fuel Cell Glass Reactors (each chamber 250 mL volume) Jain Scientific Glass Works N/A Electrospray Ionization High-Resolution Mass Spectrometry (HR-MS-ESI): Waters Synapt G2-Si Q ToF Mass Spectrometer Waters https://www.waters.com/waters/en_IN/Mass-Spectrometry/nav.htm?cid=514257&locale=en_IN FEG-SEM-EDS: Hitachi SU8010 series Hitachi https://www.hitachi-hightech.com/global/about/news/2011/nr20110214.html Gas Calibration Unit …”

“…It also provides information for a detailed characterization of enriched cathodic biofilms via various cross-disciplinary techniques, including electrochemical, analytical, microscopic, and gene sequencing techniques. For complete details on the use and execution of this protocol, please refer to Chaudhary et al. (2021) .…”

“…For complete details on the use and execution of this protocol, please refer to Chaudhary et al. (2021) .…”

Evolution of Thermophilic Microbial Communities from a Deep-Sea Hydrothermal Chimney under Electrolithoautotrophic Conditions with Nitrate

“…They can take up electrons directly from the cathode, the electron donor, in a microbial electrochemical system (MES) for their energy and transfer it into a terminal electron acceptor. In the literature, many studies have aimed to enrich these electrotrophs within microbial communities sampled from various ecosystems [12][13][14][15][16] or to axenically grow them [17,18].…”