Abstract
Bacteria that use electron transport proteins in the membrane to produce electricity in the gut microbiome have been identified recently. However, the identification of electrogenic bacteria in the skin microbiome is almost completely unexplored. Using a ferric iron-based ferrozine assay, we have identified the skin Staphylococcus epidermidis (S. epidermidis) as an electrogenic bacterial strain. Glycerol fermentation was essential for the electricity production of S. epidermidis since the inhibition of fermentation by 5-methyl furfural (5-MF) significantly diminished the bacterial electricity measured by voltage changes in a microbial fuel cell (MFC). A small-scale chamber with both anode and cathode was fabricated in order to study the effect of ultraviolet-B (UV-B) on electricity production and bacterial resistance to UV-B. Although UV-B lowered bacterial electricity, a prolonged incubation of S. epidermidis in the presence of glycerol promoted fermentation and elicited higher electricity to suppress the effect of UV-B. Furthermore, the addition of glycerol into S. epidermidis enhanced bacterial resistance to UV-B. Electricity produced by human skin commensal bacteria may be used as a dynamic biomarker to reflect the UV radiation in real-time.
Highlights
The human skin, the largest organ in the body, is annexed by a diverse range of microorganisms that are competent in extracellular electron transfer (EET) during electricity production [1,2]
To screen the electrogenic bacteria, the plates supplemented with 2% glucose or glycerol, respectively, were overlaid with samples collected from human fecal and skin
To examine whether the activity of ferric iron (Fe3+) reduction by S. epidermidis is mediated by fermentation, bacteria were pretreated with 5-methyl furfural (5-MF), a furfural analog as a fermentation inhibitor, which can inhibit acetolactate synthase (ALS) and other enzymes in the fermentation pathway of bacteria [12,18]
Summary
The human skin, the largest organ in the body, is annexed by a diverse range of microorganisms that are competent in extracellular electron transfer (EET) during electricity production [1,2]. Bacteria, such as Staphylococcus epidermidis (S. epidermidis) and Staphylococcus capitis (S. capitis), in human skin have demonstrated distinct electrogenic capabilities which are directly analogous to those of the well-known Gram-negative exoelectrogens [2,3]. The magnitude of electricity production in MFCs depends on some factors such as the selection of electrogenic bacteria, electron donors, and electron acceptors. MFC can be used as a device to determine the electrogenicity of bacteria, it is not a high-throughput and rapid screening tool for the selection of electrogenic bacteria from the human microbiome
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