Characteristics of Fe(III) reduction by Fe(III)-reducing bacterium Clostridium butyricum LQ25 under the condition of electron shuttles

Abstract:

[Objective] This study aimed to investigate the characteristics of microbial Fe(III) reduction under the condition of adding electron shuttles. [Methods] The effects of anthraquinone-2-sulfonic acid (AQS) and riboflavin on cell growth and Fe(II) concentration by a fermenting bacterium Clostridium butyricum LQ25 were investigated. [Results] The results showed that Fe(II) concentrations were significantly different under the series of electron shuttle concentrations, Fe(OH)₃ as electron acceptor and glucose as electron donor. The highest Fe(II) concentration under Fe(III)-reducing conditions by strain LQ25 was 12.95±0.08 mg/L at the AQS concentration of 0.5 mmol/L, which was 88% higher compared to the control without added AQS. When riboflavin was added as the electron shuttle, Fe(II) concentration was 11.06±0.04 mg/L at the riboflavin concentration of 100 mg/L, which was 61% higher compared to the control. The adding of electron shuttles could change the concentration of butyrate and acetic acid in fermentation products by strain LQ25, with the increasing of relative content of acetic acid. [Conclusion] The adding of electron shuttle AQS and riboflavin could significantly promote microbial Fe(III) reduction, which will provide the experimental evidence for the mechanism of extracellular electron transfer by fermentative Fe(III)-reducing bacteria.

Key words:Clostridium butyricum LQ25;anthraquinone-2-sulfonic acid (AQS);riboflavin;Fe(II) concentration