Physiological characteristics of an intestinal electroactive strain Shewanella marisflavi UU-3-2 from Urechis unicinctus

Abstract:

[Objective] To explore the electroactive microorganism in the intestinal tract of marine annelids represented by Urechis unicinctus and characterizing its physiological and electrochemical properties.[Methods] The strain was isolated using plate scribing and identified by 16S rRNA gene sequencing. The morphology of the isolate was depicted by scanning electron microscope. High performance liquid chromatography (HPLC) was used to analyze the metabolites. The quantifications of Fe(Ⅱ) and Mn(Ⅱ) reduction were carried out by ferrozine and formaldoxime assays, respectively. Single-chamber microbial fuel cells (SCMFC) were used to test the electrochemical activity by cyclic voltammetry. [Results] A facultative anaerobic bacterium, Shewanella marisflavi UU-3-2 (with the similarity of 99.93%), was successfully isolated which was a rod bacterium with the length about 2 μm and width about 0.5 μm. The metabolic analysis showed that this strain could use sodium lactate as an electron donor, fumarate as an electron acceptor for anaerobic respiration with acetate and succinate production. Ferrozine and formaldoxime assays illustrated that Fe(Ⅲ)/Mn(Ⅳ) in the Fe₂O₃/MnO₂ were reduced. The maximum current density was 146 mA/m², and the results of cyclic voltammetry revealed that the oxidation peak and reduction peak happened at 0.14 V and -0.51 V, respectively. [Conclusion] An electrochemical activity microbe, Shewanella marisflavi UU-3-2, was successfully isolated from marine animals represented by Urechis unicinctus, indicating the widespread existence of electrochemical activity microorganisms in marine annelids' intestine.