Isolation and Characterization of Human Gut Bacteria Capable of Extracellular Electron Transport by Electrochemical Techniques

Abstract

Microorganisms are known to exhibit extracellular electron transfer (EET) in a wide variety of habitats. However, as for the human microbiome which significantly impacts our health, the role and importance of EET has not been widely investigated. In this study, we enriched and isolated the EET-capable bacteria from human gut microbes using an electrochemical enrichment method and examined whether the isolates couple EET with anaerobic respiration or fermentation. Upon the use of energy-rich or minimum media (with acetate or lactate) for electrochemical enrichment with the human gut sample at an electrode potential of +0.4 V [vs. the standard hydrogen electrode (SHE)], both culture conditions showed significant current production. However, EET-capable pure strains were enriched specifically with minimum media, and subsequent incubation using the δ-MnO2-agar plate with lactate or acetate led to the isolation of two EET-capable microbial strains, Gut-S1 and Gut-S2, having 99% of 16S rRNA gene sequence identity with Enterococcus avium (E. avium) and Klebsiella pneumoniae (K. pneumoniae), respectively. While the enrichment involved anaerobic respiration with acetate and lactate, further electrochemistry with E. avium and K. pneumoniae revealed that the glucose fermentation was also coupled with EET. These results indicate that EET couples not only with anaerobic respiration as found in environmental bacteria, but also with fermentation in the human gut.

iTRAQ-Based Comparative Proteomic Analysis of Acinetobacter baylyi ADP1 Under DNA Damage in Relation to Different Carbon Sources

“…In contrast, proteins belonging to electron transporter/ transporter were mostly up-regulated, e.g., electron transfer flavoprotein beta-subunit (1.7 ± 0.3), tryptophan synthase beta chain (1.5 ± 0.3), and oxidoreductase related to nitroreductase (2.0 ± 0.3). This was in accordance with the accelerated energy production rates in nutrient-deficient media (Figure 4), as electron transporters/transporters play critical roles in aerobic respiration and serve as the most typical way for bacteria to gain energy (Bjerg et al, 2018;Naradasu et al, 2019). Across carbon source treatments, profiles of stress-related proteins in MMC treatment behaved significantly different in comparison with others.…”

Two Routes for Extracellular Electron Transfer in Enterococcus faecalis

“…Recent studies have revealed EET in the mammalian gut and identified other electroactive gut bacteria (6)(7)(8). Knowledge about the mechanisms behind EET in bacteria is not only of clinical relevance but very important for biotechnical applications such as in the design of microbial fuel cells.…”

A Human Pathogen <i>Capnocytophaga Ochracea</i> Exhibits Current Producing Capability

“…22 Metabolites were measured as previously described. 11 Glucose concentrations were measured by using a glucose assay kit (GAGO-20, Sigma-Aldrich) according to the manufacturer's instructions.…”

“…8 In particular, the identification of flavin-based enzymes in L. monocytogenes, a human pathogen, implies divergent EET mechanisms in the human microbiome. Further, Enterococcus faecalis 9,10 and two other isolates from the human gut share high homology with Klebsiella pneumoniae and Enterococcus avium, with respect to the 16S rRNA gene sequence, 11 and are capable of EET. Their EET potential may facilitate their colonization in the host environment, similar to EET in the natural environment.…”