Sensitive detection of low-concentration sulfide based on the synergistic effect of rGO, np-Au, and recombinant microbial cell.

With the aggravation of sulfide pollution, more and more attention has been paid to the detection of sulfide in the environment. However, the detection of low-concentration sulfide is still a technical bottleneck to be solved urgently. In this study, a synergistic effect strategy that combines the co-catalysis of nanoporous gold (np-Au) and recombinant microbial cell with the excellent electrical conductivity of reduced graphene oxide (rGO) was proposed for the sensitive detection of low-concentration sulfide. A rGO/np-Au composite was fabricated and then used as an immobilization support for the bio-recognition element of recombinant Escherichia coli (E. coli) over-expressed sulfide: quinone oxidoreductase (SQR). A microbial biosensor (E. coliSQR/rGO/np-Au/GCE) was successfully constructed for the sensitive detection of low-concentration sulfide. Due to the synergistic effect of rGO, np-Au, and E. coliSQR cells, the sensitivity of the proposed microbial biosensor towards sulfide reached 400.42 µA mM-1 cm-2 with a wide linear response ranging from 100 nM to 7 mM, as well as a low detection limit of 98.5 nM using amperometric i-t curve method. Furthermore, the microbial biosensor was successfully applied to the detection of sulfide in wastewater with strong anti-interference ability, high reproducibility, and strong stability. These results confirmed that the proposed microbial biosensor was ideal for the detection of low-concentration sulfide in a reliable, specific, and sensitive way.

Power generation and microbial community analysis in microbial fuel cells: A promising system to treat organic acid fermentation wastewater.

To explore a sustainable and efficient treatment approach for organic acid fermentation wastewater, two microbial fuel cells (MFCs) systems inoculated with wastewater or domesticated microbial community were constructed in this study. Compared with the MFC inoculated with domesticated microbial community, the MFC inoculated with wastewater not only showed higher power density (543.75 mW m-2) and coulomb efficiency (22.10%), but also exhibited higher removal rates of chemical oxygen demand (75.59%), total nitrogen (76.15%), and ammonia nitrogen (83.23%), meeting the demand of wastewater discharge standard of China. Sequencing analysis revealed that the MFC inoculated with wastewater were richer in microbial community, and some bacteria such as Saprospiraceae and Caldilineaceae were beneficial for its good performance. In contrast, the microbial community of the MFC inoculated with domesticated microbial community was relatively simple. These results indicated that MFCs may be a sustainable method for organic acid fermentation wastewater treatment without any preprocessing.

Highly sensitive microbial biosensor based on recombinant Escherichia coli overexpressing catechol 2,3-dioxygenase for reliable detection of catechol.

A highly sensitive whole cell based electrochemical biosensor was developed for catechol detection in this study. The carE gene of Sphingobium yanoikuyae XLDN2-5 encoding catechol 2,3-dioxygenase (C23O), a key enzyme in the biodegradation of aromatic compound, was cloned and over-expressed in Escherichia coli BL21 (E. coli BL21). Compared to Sphingobium yanoikuyae XLDN2-5, the recombinant E. coli BL21 over-expressed C23O exhibited higher catalytic activity towards catechol. Moreover, the whole cells provided a better environment for C23O to maintain its catalytic activity and stability compared with crude enzyme. The distinctive features of the recombinant E. coli BL21 over-expressed C23O made it an ideal bio-recognition element for the fabrication of a microbial biosensor. Additionally, nanoporous gold (NPG) with unique properties of structure and function was selected as a support to immobilized the recombinant E. coli BL21 over-expressed C23O. Based on the synergistic effect of C23O and NPG, the E. coli BL21-C23O/NPG/GCE bioelectrode showed a good linear response for catechol detection ranging from 1 µM to 500 µM with a high sensitivity of 332.24 µA mM-1 cm-2 and a low detection limit of 0.24 µM. Besides, the E. coli BL21-C23O/NPG/GCE bioelectrode exhibited strong anti-interference and good stability. For the detection of catechol in wastewater samples, the concentrations detected by the E. coli BL21-C23O/NPG/GCE bioelectrode were in good agreement with the standard concentrations that added in the wastewater samples, which make the E. coli BL21-C23O/NPG/GCE bioelectrode an ideal tool for reliable catechol detection.

Bacterial electroactivity and viability depends on the carbon nanotube-coated sponge anode used in a microbial fuel cell.

The anode material is vital to improve the power generation of a microbial fuel cell (MFC). In this study, a carbon nanotube (CNT)-coated sponge with macro-porous structure, high surface area, and high conductivity was constructed as an anode to encapsulate Escherichia coli K12 (E. coli K12) cells. To achieve high power generation of the MFC, the optimal concentration of the CNT coating the sponge was found to be 30mgmL-1. At this concentration, a maximum power density of 787Wm-3 and a chemical oxygen demand (COD) removal of 80.9% were obtained with a long stable electricity generation process in batch mode. This indicates that the biofilm on the CNT (30mgmL-1)-coated sponge possessed excellent electroactivity and stability. Scanning electron microscope (SEM) images confirmed that the CNT-coated sponge provided a suitable microenvironment for E. coli K12 cells to maintain their attachment and colonization. Additionally, a CNT-dependent viability phenomenon of the E. coli K12 cells was discovered after electricity generation. This CNT-dependent viability of the E. coli K12 cells was stable and sustainable after storage at -20°C in a milk tube for one year.