Analysis and enhancement of the energy utilization efficiency of corn stover using strain Lsc-8 in a bioelectrochemical system.

The strain Lsc-8 can produce a current density of 33.08 µA cm-2 using carboxymethylcellulose (CMC) as a carbon source in a three-electrode configuration. A co-culture system of strain Lsc-8 and Geobacter sulfurreducens PCA was used to efficiently convert cellulose into electricity to improve the electricity generation capability of microbial fuel cells (MFCs). The maximum current density achieved by the co-culture with CMC was 559 µA cm-2, which was much higher than that of strain Lsc-8 using CMC as the carbon source. The maximum power density reached 492.05 ± 52.63 mW cm-2, which is much higher than that previously reported. Interaction mechanism studies showed that strain Lsc-8 had the ability to secrete riboflavin and convert cellulose into acetic acid, which might be the reason for the high electrical production performance of the co-culture system. In addition, to the best of our knowledge, a co-culture or single bacteria system using agricultural straw as the carbon source to generate electricity has not been reported. In this study, the maximum current density of the three-electrode system inoculated with strain Lsc-8 was 14.56 µA cm-2 with raw corn stover as the sole carbon source. Raw corn stover as a carbon source was also investigated for use in a co-culture system. The maximum current density achieved by the co-culture was 592 µA cm-2. The co-culture system showed a similar electricity generation capability when using raw corn stover and when using CMC. This research shows for the first time that a co-culture or single bacteria system can realize both waste biomass treatment and waste power generation.

Physiological and transcriptional studies reveal Cr(VI) reduction mechanisms in the exoelectrogen Cellulomonas fimi Clb-11.

A facultative exoelectrogen, Cellulomonas fimi strain Clb-11, was isolated from polluted river water. This strain could generate electricity in microbial fuel cells (MFCs) with carboxymethyl cellulose (CMC) as the carbon source, and the maximum output power density was 12.17 ± 2.74 mW·m-2. In addition, Clb-11 could secrete extracellular chromate reductase or extracellular electron mediator to reduce Cr(VI) to Cr(III). When the Cr(VI) concentration was less than 0.5 mM in Luria-Bertani (LB) medium, Cr(VI) could be completely reduced by Clb-11. However, the Clb-11 cells swelled significantly in the presence of Cr(VI). We employed transcriptome sequencing analysis to identify genes involved in different Cr(VI) stress responses in Clb-11. The results indicate that 99 genes were continuously upregulated while 78 genes were continuously downregulated as the Cr(VI) concentration increased in the growth medium. These genes were mostly associated with DNA replication and repair, biosynthesis of secondary metabolites, ABC transporters, amino sugar and nucleotide sugar metabolism, and carbon metabolism. The swelling of Clb-11 cells might have been related to the upregulation of the genes atoB, INO1, dhaM, dhal, dhak, and bccA, which encode acetyl-CoA C-acetyltransferase, myo-inositol-1-phosphate synthase, phosphoenolpyruvate-glycerone phosphotransferase, and acetyl-CoA/propionyl-CoA carboxylase, respectively. Interestingly, the genes cydA and cydB related to electron transport were continuously downregulated as the Cr(VI) concentration increased. Our results provide clues to the molecular mechanism of Cr(VI) reduction by microorganisms in MFCs systems.

Electricity production of microbial fuel cells by degrading cellulose coupling with Cr(VI) removal.

A facultative exoelectrogen strain Lsc-8 belonging to the Cellulomonas genus with the ability to degrade carboxymethyl cellulose (CMC) coupled with the reduction of Cr(VI), was successfully isolated from rumen content. The maximum output power density of the microbial fuel cells (MFCs) inoculated strain Lsc-8 was 9.56 ±â€¯0.37 mW·m-2 with CMC as the sole carbon source. From the biomass analysis it can be seen that the electricity generation of the MFCs was primarily attributed to the planktonic cells of strain Lsc-8 rather than the biofilm attached on the electrode, which was different from Geobacter sulfurreducens. Especially, during electricity generation of the MFCs using CMC as carbon source in the anode chamber, the Cr(VI) reduction were simultaneously realized. And it is also found that the Cr(VI) reduction ratio by strain Lsc-8 is directly related to the initial Cr(VI) concentration, and it increased with the increase of initial Cr(VI) concentration at first, then started to decrease when the Cr(VI) concentration was above 21 mg ·L-1. Meanwhile, the highest output power density of 3.47 ±â€¯0.28 mW·m-2 was observed coupling with 95.22 ±â€¯2.72 % of Cr(VI) reduction. These data suggested that the strain Lsc-8 could reduce high toxicity Cr(VI) to low toxicity Cr(III) coupled with electricity generation in MFCs with CMC as the carbon source. Our results also suggested that this study will provide a possibility to simultaneously degrade Cr(VI) and generate electricity by using cellulose as the carbon source via MFCs.

Harvesting energy from cellulose through Geobacter sulfurreducens in Unique ternary culture.

In this study, both electricity generation capability and biodegradation process of carboxymethyl cellulose (CMC) were investigated using a defined ternary culture of Paenibacillus sp., Klebsiella sp. and Geobacter sulfurreducens as biocatalysts in MFCs. The maximum current density achieved by the ternary culture from CMC was 621 ±â€¯23 µA cm-2 in half-cell experiments and the maximum power density reached to 1146 ±â€¯28 mW m-2 in two-chamber MFCs. Meanwhile, the ternary culture also possessed three times higher CMC degradation capability compared to the pure strain J1. Besides, the key metabolite products, including cellobiose, glucose, acetate, were quantified by high performance liquid chromatography (HPLC) to illustrate the biodegradation process of CMC. The high electricity generation performance mainly resulted from the "division-of-labor" based cooperation and the enhanced extracellular electron transfer caused by the electron shuttle secreted by Klebsiella sp. This study highlighted the synergistic effect of specific community on electricity generation using CMC as carbon source, and laid the foundation for further optimization of more efficient and stable microbial consortia for bioenergy applications.