Enhancement of dissimilatory nitrate/nitrite reduction to ammonium of Escherichia coli sp. SZQ1 by ascorbic acid: Mechanism and performance

Bifunctional sludge-derived redox carbon dots with photoelectron storage and delivery properties for ammonia production by photosensitized Shewanella oneidensis MR-1

Combining the light-harvesting capabilities of photosensitizers with microbial catalysis shows great potential in solar-driven biomanufacturing. However, little information is available about the effects of photosensitizers on the photoelectron transport during the dissimilatory nitrate reduction to ammonium (DNRA) process. Herein, redox carbon dots (CDs-500) were prepared from sludge via the pyrolysis-Fenton reaction and then used to construct a photosynthetic system with Shewanella oneidensis MR-1. The MR-1/CDs-500 photosynthetic system showed a 5.9-fold increase in ammonia production (4.9 mmol(NH3)·g-1(protein)·h-1) with a high selectivity of 94.0 %. The photoelectrons were found to be stored in CDs-500 and transferred into the cells. During the inward electron transport, the intracellular CDs-500 could be used as the direct photoelectron transfer stations between outer membrane cytochrome c and DNRA-related enzymes without the involvement of CymA and MtrA. This work provides a new method for converting waste into functional catalysts and increases solar-driven NH3 production to a greater extent.

Impact of bioelectricity on DNRA process and microbial community composition within cathodic biofilms in dual-chambered bioelectrode microbial fuel cell (MFC)

The synchronous bioelectricity generation and dissimilatory nitrate reduction to ammonium (DNRA) pathway in Klebsiella variicola C1 was investigated. The presence of bioelectricity facilitated cell growth on the anodic biofilms, consequently enhancing the nitrate removal efficiency decreasing total nitrogen levels and causing a negligible accumulation of NO2- in the supernatant. Genomic analysis revealed that K. variicola C1 possessed a complete DNRA pathway and largely annotated electron shuttles. The up-regulated expression of genes narG and nirB, encoding nitrite oxidoreductase and nitrite reductase respectively, was closely associated with increased extracellular electron transfer (EET). High-throughput sequencing analysis was employed to investigate the impact of bioelectricity on microbial community composition within cathodic biofilms. Results indicated that Halomonas, Marinobacter and Prolixibacteraceae were enriched at the cathode electrodes. In conclusion, the integration of a DNRA strain with MFC facilitated the efficient removal of wastewater containing high concentrations of NO3- and enabled the environmentally friendly recovery of NH4+.

Review of the mechanisms involved in dissimilatory nitrate reduction to ammonium and the efficacies of these mechanisms in the environment

Dissimilatory nitrate reduction to ammonium (DNRA) is currently of great interest because it is an important method for recovering nitrogen from wastewater and offers many advantages, over other methods. A full understanding of DNRA requires the mechanisms, pathways, and functional microorganisms involved to be identified. The roles these pathways play and the effectiveness of DNRA in the environment are not well understood. The objectives of this review are to describe our current understanding of the molecular mechanisms and pathways involved in DNRA from the substrate transfer perspective and to summarize the effects of DNRA in the environment. First, the mechanisms and pathways involved in DNRA are described in detail. Second, our understanding of DNRA by actinomycetes is reviewed and gaps in our understanding are identified. Finally, the effects of DNRA in the environment are assessed. This review will help in the development of future research into DNRA to promote the use of DNRA to treat wastewater and recover nitrogen.

A Symbiotic Fungus Sistotrema Benefits Blueberry Rejuvenation and Abiotic Stress Tolerance

Blueberry (Vaccinium spp.) rhizosphere microorganisms can significantly increase the absorption area and improve the efficiency of rhizospheric nutrient uptake. However, there has been little research on blueberry rhizosphere microorganisms, especially those that can complement root function deficiency. In this study, we analyzed the rhizosphere fungi of 'O'Neal,' 'Sharpblue,' and 'Premier' blueberry cultivars and found that 'Premier' blueberries showed strong growth potential and relatively high root regulation ability. The dominant symbiotic fungus Sistotrema was correlated with the strong growth of 'Premier' and was directionally screened and isolated based on conserved gene structures and COG function analysis. This fungus was reinoculated onto the roots of 'Gulfcoast' and 'Star' blueberry cultivars. Sistotrema promoted the growth of blueberries and improved their ability to resist stress and grow under adverse conditions, as indicated by maintained or increased chlorophyll content under such conditions. Further analyses showed that Sistotrema has certain functional characteristics such as the ability to dissolve iron in its insoluble form and then release it, to fix nitrogen, and to inhibit nitrification in soil. Thus, it effectively doubled the soil nitrogen content and increased the soluble iron content in soil by 50%. This investigation indicates sistotrema inoculation as an approach to increase blueberry stress tolerance and complete their root nutrition deficiency.