Isolation of Fe(III)-reducing bacterium Clostridium sp. LQ25 and characteristics of Fe(III) reduction and hydrogen production

Abstract:

[Background] Some dissimilatory Fe(III)-reducing bacteria have the ability of dissimilatory iron reduction and fermentative hydrogen production, which can provide an important way to study the mechanism of fermentative Fe(III)-reducing bacteria. [Objective] This study aimed to screen a fermentative Fe(III)-reducing bacterium with the characteristics of microbial Fe(III) reduction and hydrogen production. [Methods] The strain was screened by three-layer plate method and identified by sequencing the 16S rRNA gene. Fe(II) concentration and hydrogen production were investigated to analyze the characteristics of microbial Fe(III)-reducing and hydrogen-producing by this strain. [Results] Compared to Clostridium butyricum, the similarity was 100% by strain LQ25 based on 16S rRNA gene sequence. The results show that cell growth by strain LQ25 under Fe(III)-reducing conditions using Fe(OH)₃ as electron acceptor were significantly enhanced compared with the control (no adding Fe(III)). Strain LQ25 was able to grow, reduce Fe(III) and produce hydrogen when using pyruvate, glucose and lactate as electron donor respectively. The highest Fe(II) concentration and cell growth by strain LQ25 was achieved when pyruvate was used as electron donor, with protein content (78.88±3.40) mg/L and Fe(II) concentration (8.27±0.23) mg/L. When glucose was used as electron donor, hydrogen production was (475.2±14.4) mL/L under Fe(III)-reducing conditions with the adding Fe(III), which was 87.7% higher compared to the control (no adding Fe(III)). [Conclusion] A fermentative Fe(III)-reducing bacterium Clostridium sp. LQ25 which is capable of microbial Fe(III) reduction and hydrogen production was successfully screened in this study. The result will provide new experimental evidence for the mechanism of extracellular electron transfer by fermentative Fe(III)-reducing bacteria.