Microbial electroactive biofilms dominated by Geoalkalibacter spp. from a highly saline\u2013alkaline environment

Sukrampal Yadav,Sunil A. Patil

doi:10.1038/s41522-020-00147-7

Abstract

Understanding of the extreme microorganisms that possess extracellular electron transfer (EET) capabilities is pivotal to advance electromicrobiology discipline and to develop niche-specific microbial electrochemistry-driven biotechnologies. Here, we report on the microbial electroactive biofilms (EABs) possessing the outward EET capabilities from a haloalkaline environment of the Lonar lake. We used the electrochemical cultivation approach to enrich haloalkaliphilic EABs under 9.5 pH and 20 g/L salinity conditions. The electrodes controlled at 0.2 V vs. Ag/AgCl yielded the best-performing biofilms in terms of maximum bioelectrocatalytic current densities of 548 ± 23 and 437 ± 17 µA/cm2 with acetate and lactate substrates, respectively. Electrochemical characterization of biofilms revealed the presence of two putative redox-active moieties with the mean formal potentials of 0.183 and 0.333 V vs. Ag/AgCl, which represent the highest values reported to date for the EABs. 16S-rRNA amplicon sequencing of EABs revealed the dominance of unknown Geoalkalibacter sp. at ~80% abundance. Further investigations on the haloalkaliphilic EABs possessing EET components with high formal potentials might offer interesting research prospects in electromicrobiology.

Highlights

Electromicrobiology is a new subdiscipline of microbiology, which deals with the study of electrochemical interactions or extracellular electron transfer (EET) processes between microorganisms and the solid-state electron acceptors or donors, and their implications in different environments[1,2]
We present the electrochemical enrichment and characterization of the exoelectrogenic microorganisms from the
Neither any redox peak nor deviation in the faradic current densities was observed in the CVs recorded with the new electrodes in filtered spent media from both acetate- and lactate-fed reactors (Fig. 2c). These observations suggest that no soluble redox-active components or mediators were secreted in the medium by the enriched microbial electroactive biofilms (EABs) on the completion of batch experiments, and thereby confirm that the electron transfer and bioelectrocatalytic current generation was due to the electrode-associated biofilms and most likely via direct electron transfer mechanism

Summary

Introduction

Electromicrobiology is a new subdiscipline of (environmental) microbiology, which deals with the study of electrochemical interactions or extracellular electron transfer (EET) processes between microorganisms and the solid-state electron acceptors or donors, and their implications in different environments[1,2]. These observations suggest that no soluble redox-active components or mediators were secreted in the medium by the enriched microbial EAB on the completion of batch experiments, and thereby confirm that the electron transfer and bioelectrocatalytic current generation was due to the electrode-associated biofilms and most likely via direct electron transfer mechanism.

Results

Conclusion