Engineering extracellular electron transfer to promote simultaneous brewing wastewater treatment and chromium reduction.

Microbial fuel cell (MFC) technology has been developed for wastewater treatment in the anodic chamber, and heavy metal reduction in the cathodic chamber. However, the limited extracellular electron transfer (EET) rate of exoelectrogens remained a constraint for practical applications of MFCs. Here, a MFC system that used the electricity derived from anodic wastewater treatment to drive cathodic Cr6+ reduction was developed, which enabled an energy self-sustained approach to efficiently address Cr6+ contamination. This MFC system was achieved by screening exoelectrogens with a superior EET rate, promoting the exoelectrogenic EET rate, and constructing a conductive bio-anode. Firstly, Shewanella algae-L3 was screened from brewing wastewater acclimatized sludge, which generated power density of 566.83 mW m-2. Secondly, to facilitate EET rate, flavin synthesis gene operon ribADEHC was overexpressed in engineered S. algae-L3F to increase flavins biosynthesis, which promoted the power density to 1233.21 mW m-2. Thirdly, to facilitate interface electron transfer, carbon nanotube (CNT) was employed to construct a S. algae-L3F-CNT bio-anode, which further enhanced power density to 3112.98 mW m-2. Lastly, S. algae-L3F-CNT bio-anode was used to harvest electrical energy from brewing wastewater to drive cathodic Cr6+ reduction in MFC, realizing 71.43% anodic COD removal and 98.14% cathodic Cr6+ reduction. This study demonstrated that enhanced exoelectrogenic EET could facilitate cathodic Cr6+ reduction in MFC.

Enhancement of Acid Protease Activity of Aspergillus oryzae Using Atmospheric and Room Temperature Plasma.

Atmospheric and room temperature plasma (ARTP) system is a novel and efficient mutagenesis protocol for microbial breeding. In this study, ARTP was employed to treat spores of Aspergillus oryzae strain 3.042 for selection of high acid protease producers. With an irradiation time of 150 s at the lethal rate of 90%, 19 mutants with higher acid protease activity were initially selected based on different mutant colony morphology and ratio of the clarification halo of protease activity to the colony diameter. Measurements of the acid protease activity revealed that mutant strain B-2 is characterized by a steady hereditary stability with increased acid protease, neutral protease and total protease activities of 54.7, 17.3, and 8.5%, respectively, and decreased alkaline protease activity of 8.1%. In summary, the identified mutant strain B-2 exhibits great potential for the enhancement of the insufficient acid protease activity during the middle and later stages of soy sauce fermentation.

Comparative analysis of rhamnolipid congener synthesis in neotype Pseudomonas aeruginosa ATCC 10145 and two marine isolates.

A comparative study of rhamnolipid congener synthesis was performed using the neotype Pseudomonas aeruginosa ATCC 10145 and two marine isolates (1A01151 and 1A00364). Compared with the neotype, 1A01151 and 1A00364 showed increased production of rhamnolipids containing higher proportion of congeners with longer fatty acid chains (C10-C12 and C10-C12:1) and/or di-rhamnose moiety. These could reduce surface tension of water to lower minimum values of 21.3 mN m-1 and 25.7 mN m-1. The comparative profile of rhamnolipid congener composition, fatty acid content and gene expression suggested that elevated expression of rhlAB and rhlC throughout the fermentation process and enhanced accumulation of dTDP-l-rhamnose and fatty acid precursors (C12 and C12:1) at the onset of rhamnolipid accumulation were related to improved rhamnolipid production and surface-active property. This work provides insights into the metabolic relationship between rhamnolipids and related precursor biosynthesis, and could therefore be beneficial for process optimization for efficient rhamnolipid congener production.