Characterization of an aerobic denitrifier Enterobacter cloacae strain HNR and its nitrate reductase gene

Impact of Nitrate on the Removal of Pollutants from Water in Reducing Gas-Based Membrane Biofilm Reactors: A Review

The membrane biofilm reactor (MBfR) is a novel wastewater treatment technology, garnering attention due to its high gas utilization rate and effective pollutant removal capability. This paper outlines the working mechanism, advantages, and disadvantages of MBfR, and the denitrification pathways, assessing the efficacy of MBfR in removing oxidized pollutants (sulfate (SO4-), perchlorate (ClO4-)), heavy metal ions (chromates (Cr(VI)), selenates (Se(VI))), and organic pollutants (tetracycline (TC), p-chloronitrobenzene (p-CNB)), and delves into the role of related microorganisms. Specifically, through the addition of nitrates (NO3-), this paper analyzes its impact on the removal efficiency of other pollutants and explores the changes in microbial communities. The results of the study show that NO3- inhibits the removal of other pollutants (oxidizing pollutants, heavy metal ions and organic pollutants), etc., in the simultaneous removal of multiple pollutants by MBfR.

Distinct gut bacterial composition in Anoplophora glabripennis reared on two host plants

Anoplophora glabripennis (Coleoptera: Cerambycidae: Lamiinae) is an invasive wood borer pest that has caused considerable damage to forests. Gut bacteria are of great importance in the biology and ecology of herbivores, especially in growth and adaptation; however, change in the gut bacterial community of this pest feeding on different hosts is largely unknown. In this study, we investigated the gut bacterial communities of A. glabripennis larvae fed on different preferred hosts, Salix matsudana and Ulmus pumila, using 16S rDNA high-throughput sequencing technology. A total of 15 phyla, 25 classes, 65 orders, 114 families, 188 genera, and 170 species were annotated in the gut of A. glabripennis larvae fed on S. matsudana or U. pumila using a 97% similarity cutoff level. The dominant phyla were Firmicutes and Proteobacteria and the core dominant genera were Enterococcus, Gibbsiella, Citrobacter, Enterobacter, and Klebsiella. There was significantly higher alpha diversity in the U. pumila group than in the S. matsudana group, and principal co-ordinate analysis showed significant differences in gut bacterial communities between the two groups. The genera with significant abundance differences between the two groups were Gibbsiella, Enterobacter, Leuconostoc, Rhodobacter, TM7a, norank, Rhodobacter, and Aurantisolimonas, indicating that the abundance of larval gut bacteria was affected by feeding on different hosts. Further network diagrams showed that the complexity of the network structure and the modularity were higher in the U. pumila group than in the S. matsudana group, suggesting more diverse gut bacteria in the U. pumila group. The dominant role of most gut microbiota was related to fermentation and chemoheterotrophy, and specific OTUs positively correlated with different functions were reported. Our study provides an essential resource for the gut bacteria functional study of A. glabripennis associated with host diet.

Characterization and metabolic pathway of Pseudomonas fluorescens 2P24 for highly efficient ammonium and nitrate removal

The ammonium and nitrate removal performance and metabolic pathways of a biocontrol strain, Pseudomonas fluorescens 2P24, were investigated. Strain 2P24 could completely remove 100 mg/L ammonium and nitrate, with removal rates of 8.27 mg/L/h and 4.29 mg/L/h, respectively. During these processes, most of the ammonium and nitrate were converted to biological nitrogen via assimilation, and only small amounts of nitrous oxide escaped. The inhibitor allylthiourea had no impact on ammonium transformation, and diethyl dithiocarbamate and sodium tungstate did not inhibit nitrate removal. Intracellular nitrate and ammonium were detectable during the nitrate and ammonium transformation process, respectively. Moreover, the nitrogen metabolism functional genes (glnK, nasA, narG, nirBD, nxrAB, nirS, nirK, and norB) were identified in the strain. All results highlighted that P. fluorescens 2P24 is capable of assimilatory and dissimilatory nitrate reduction, ammonium assimilation and oxidation, and denitrification.

Nitrogen removal intensification of aerobic granular sludge through bioaugmentation with "heterotrophic nitrification-aerobic denitrification" consortium during petroleum wastewater treatment

The bioaugmentation potential of aerobic granular sludge (AGS) was investigated using heterotrophic nitrification-aerobic denitrification (HN-AD) bacterial consortium to improve nitrogen removal during petroleum wastewater treatment. An efficient HN-AD consortium was constructed by mixing Pseudomonas mendocina K0, Brucella sp. K1, Pseudomonas putida T4 and Paracoccus sp. T9. AGS bioaugmented by immobilized HN-AD consortium enhanced nitrogen removal, which showed NH₄⁺-N and TN removal efficiency of 92.4% and 79.8%, respectively. The immobilized consortium addition facilitated larger AGS formation, while granules > 2.0 mm accounted for 16.7% higher than that of control (6.7%). Further, the abundance of napA gene was 4-times higher in the bioaugmented AGS as compared to the control, which demonstrated the long-term stability of HN-AD consortium in the bioreactor. The bioaugmented AGS also showed a higher abundance of xenobiotics biodegradation and nitrogen metabolism. These results highlight that bioaugmentation of AGS technology could be effectively used for enhanced denitrification of petroleum wastewater.

How bioaugmentation with Comamonas testosteroni accelerates pyridine mono-oxygenation and mineralization

Pyridine is a common heterocycle found in industrial wastewaters. Its biodegradation begins with a mono-oxygenation reaction, and bioaugmentation with bacteria able to carry out this mono-oxygenation is one strategy to improve pyridine removal and mineralization. Although bioaugmentation has been used to enhance the biodegradation of recalcitrant organic compounds, the specific role played by the bioaugmented bacteria usually has not been addressed. We acclimated activated-sludge biomass for pyridine biodegradation and then isolated a strain -- Comamonas testosteroni -- based on its ability to biodegrade and grow on pyridine alone. Pyridine was removed faster by C. testosteroni, compared to pyridine-acclimated biomass, but pyridine mineralization was slower. Pyridine biodegradation and mineralization rates were accelerated when C. testosteroni was bioaugmented into the acclimated biomass, which increased the amount of C. testosteroni, but otherwise had minimal effects on the microbial community. The key role of C. testosteroni was to accelerate the first step of pyridine biodegradation, mono-oxygenation to 2-hydroxylpyridine (2HP), and the acclimated biomass was better able to complete downstream reactions leading to mineralization. Thus, bioaugmentation increased the rates of pyridine mono-oxygenation and subsequent mineralization through the synergistic roles of C. testosteroni and the main community in the acclimated biomass.

Treatment of Low C/N Ratio Wastewater by a Carbon Cloth Bipolar Plate Multicompartment Electroenhanced Bioreactor (CBM-EEB)

The traditional biological denitrification process has the problems of low removal rates and lack of a carbon source when treating wastewater with high ammonia nitrogen concentration and a low carbon-nitrogen ratio. Based on a bio-electrochemical system (BES), a novel carbon cloth bipolar plate multicompartment electroenhanced bioreactor (CBM-EEB) system was constructed. In this study, nitrogen removal efficiency and enrichment of functional bacteria using CBM-EEB under different voltage conditions were investigated. The results from next-generation sequencing indicated that the CBM-EEB included heterotrophic nitrification and aerobic denitrification (HNAD) and was dominated by heterotrophic nitrification aerobic denitrifying bacteria (HNADB). The applied voltage was confirmed as having the ability to regulate the microbial community structure and abundance of functional genes, thereby further enhancing the nitrogen removal efficiency of the system. The total nitrogen removal efficiency was 77.70 ± 1.14, 87.10 ± 0.56, 86.40 ± 0.59, and 89.30 ± 0.53% under applied voltages of 0.4, 0.7, 1.0, and 1.3 V, respectively. All values were significantly higher than the control group (62.86 ± 2.06%). HNADB had the highest abundance among the 17 detected genera related to nitrogen metabolism. Facultative denitrifying bacteria, Pseudoxanthomonas, along with key bacteria of HNADB, such as Flavobacterium, constructed a shortcut simultaneous nitrification-denitrification (SND) process. Poisson analysis and redundancy analysis (RDA) showed that the applied voltage improved the denitrification efficiency by changing the microbial community structure, reducing the abundance of heterotrophic bacteria, and increasing the unit abundance of key functional genes so that less organics were required for the denitrification process. The increased nitrogen removal efficiency in the experimental group was mainly related to simultaneous nitrification-denitrification process and cooperation of microbial communities in the anode and the cathode. This study highlighted the feasibility of CBM-EEB to enhance the HNAD reaction and the response of wastewater with a low C/N ratio to enhance the abundance of microbial bacteria and their functional gene abundance.