Heterotrophic nitrogen removal in Bacillus sp. K5: involvement of a novel hydroxylamine oxidase

Unraveling the mechanisms behind sodium persulphate-induced changes in petroleum-contaminated aquifers' biogeochemical parameters and microbial communities

Sodium persulphate (PS) is a highly effective oxidising agent widely used in groundwater remediation and wastewater treatment. Although numerous studies have examined the impact of PS with respect to the removal efficiency of organic pollutants, the residual effects of PS exposure on the biogeochemical parameters and microbial ecosystems of contaminated aquifers are not well understood. This study investigates the effects of exposure to different concentrations of PS on the biogeochemical parameters of petroleum-contaminated aquifers using microcosm batch experiments. The results demonstrate that PS exposure increases the oxidation-reduction potential (ORP) and electrical conductivity (EC), while decreasing total organic carbon (TOC), dehydrogenase (DE), and polyphenol oxidase (PO) in the aquifer. Three-dimensional excitation-emission matrix (3D-EEM) analysis indicates PS is effective at reducing fulvic acid-like and humic acid-like substances and promoting microbial metabolic activity. In addition, PS exposure reduces the abundance of bacterial community species and the diversity index of evolutionary distance, with a more pronounced effect at high PS concentrations (31.25 mmol/L). Long-term (90 d) PS exposure results in an increase in the abundance of microorganisms with environmental resistance, organic matter degradation, and the ability to promote functional genes related to biological processes such as basal metabolism, transmission of genetic information, and cell motility of microorganisms. Structural equation modeling (SEM) further confirms that ORP and TOC are important drivers of change in the abundance of dominant phyla and functional genes. These results suggest exposure to different concentrations of PS has both direct and indirect effects on the dominant phyla and functional genes by influencing the geochemical parameters and enzymatic activity of the aquifer. This study provides a valuable reference for the application of PS in ecological engineering.

Phylogenetic diversity, distribution, and gene structure of the pyruvic oxime dioxygenase involved in heterotrophic nitrification

Some heterotrophic microorganisms carry out nitrification to produce nitrite and nitrate from pyruvic oxime. Pyruvic oxime dioxygenase (POD) is an enzyme that catalyzes the degradation of pyruvic oxime to pyruvate and nitrite from the heterotrophic nitrifying bacterium Alcaligenes faecalis. Sequence similarity searches revealed the presence of genes encoding proteins homologous to A. faecalis POD in bacteria of the phyla Proteobacteria and Actinobacteria and in fungi of the phylum Ascomycota, and their gene products were confirmed to have POD activity in recombinant experiments. Phylogenetic analysis further classified these POD homologs into three groups. Group 1 POD is mainly found in heterotrophic nitrifying Betaproteobacteria and fungi, and is assumed to be involved in heterotrophic nitrification. It is not clear whether group 2 POD, found mainly in species of the Gammaproteobacteria and Actinobacteria, and group 3 POD, found simultaneously with group 1 POD, are involved in heterotrophic nitrification. The genes of bacterial group 1 POD comprised a single transcription unit with the genes related to the metabolism of aromatic compounds, and many of the genes group 2 POD consisted of a single transcription unit with the gene encoding the protein homologous to 4-hydroxy-tetrahydrodipicolinate synthase (DapA). LysR- or Cro/CI-type regulatory genes were present adjacent to or in the vicinity of these POD gene clusters. POD may be involved not only in nitrification, but also in certain metabolic processes whose functions are currently unknown, in coordination with members of gene clusters.

Novel Alcaligenes ammonioxydans sp. nov. from wastewater treatment sludge oxidizes ammonia to N2 with a previously unknown pathway

Heterotrophic nitrifiers are able to oxidize and remove ammonia from nitrogen-rich wastewaters but the genetic elements of heterotrophic ammonia oxidation are poorly understood. Here, we isolated and identified a novel heterotrophic nitrifier, Alcaligenes ammonioxydans sp. nov. strain HO-1, oxidizing ammonia to hydroxylamine and ending in the production of N₂ gas. Genome analysis revealed that strain HO-1 encoded a complete denitrification pathway but lacks any genes coding for homologous to known ammonia monooxygenases or hydroxylamine oxidoreductases. Our results demonstrated strain HO-1 denitrified nitrite (not nitrate) to N₂ and N₂ O at anaerobic and aerobic conditions respectively. Further experiments demonstrated that inhibition of aerobic denitrification did not stop ammonia oxidation and N₂ production. A gene cluster (dnfT1RT2ABCD) was cloned from strain HO-1 and enabled E. coli accumulated hydroxylamine. Sub-cloning showed that genetic cluster dnfAB or dnfABC already enabled E. coli cells to produce hydroxylamine and further to ¹⁵ N₂ from (¹⁵ NH₄ )₂ SO₄ . Transcriptome analysis revealed these three genes dnfA, dnfB and dnfC were significantly upregulated in response to ammonia stimulation. Taken together, we concluded that strain HO-1 has a novel dnf genetic cluster for ammonia oxidation and this dnf genetic cluster encoded a previously unknown pathway of direct ammonia oxidation (Dirammox) to N₂ .

Isolation of two iron-reducing facultative anaerobic electricigens and probing the application performance in eutrophication water

Purpose

Sediment microbial fuel cell (SMFC) is a promising bioremediation technology in which microbes play an important role. Electricigens as the bio-catalysts have effect on pollution control and electricity generation. It is of great significance to screen the microorganisms with the ability of generating electricity.

Methods

The SMFC anode biofilm was used as microbiological source to study the feasibility of electricigens with iron-reducing property for eutrophication water treatment. Preliminarily, we isolated 20 facultative anaerobic pure bacteria and evaluated their cyclic voltammogram (CV) through the three-electrode system and electrochemical workstation. The power generation performance of strains was verified by air-cathode microbial fuel cells (AC-MFCs) under different single carbon sources.

Result

According to its morphological, physiological, and biochemical characteristics, along with phylogenetic analysis, the two strains (SMFC-7 and SMFC-17) with electrical characteristics were identified as Bacillus cereus. Compared with SMFC-7, SMFC-17 exhibited efficient NH4+-N and NO3−-N removal and PO43−-P accumulation from eutrophic solution with a removal rate of 79.91 ± 6.34% and 81.26 ± 1.11% and accumulation rate of 57.68 ± 4.36%, respectively.

Conclusion

The isolated bacteria SMFC-17 showed a good performance in eutrophic solution, and it might be a useful biocatalyst to enable the industrialized application of SMFC in eutrophic water treatment.

Optimization, purification, and characterization of hydroxylamine oxidoreductase from Acinetobacter sp. Y1

Hydroxylamine oxidoreductase (HAO) is a key enzyme involved in ammonium removal pathway. To further study the enzyme, HAO was purified from heterotrophic nitrifier Acinetobacter sp. Y1 and its property was investigated. Results of single-factor experiments showed that the optimal carbon source, nitrogen source, and C/N ratio were trisodium citrate, ammonium sulfate, and 14, respectively, with incubation time of 16 H. DEAE Sefinose^TM FF anion-exchange chromatography was used to purify HAO, followed by Sefinose^TM CL-6B gel filtration chromatography. SDS-PAGE revealed that a 47 kDa enzyme was purified successfully, with a purification fold of 7.32 and a recovery rate of 19.40%. The optimized enzyme activity of purified HAO was tested at pH 8.0 and 30 °C. The results showed that the activity was increased by 43.78% and 25.64% in the presence of 1 mM Fe²⁺ and Fe³⁺ , respectively. HAO activity was increased with the increase of Na⁺ and K⁺ , Mn²⁺ , Zn²⁺ , Cu²⁺ , Ca²⁺ , Ba²⁺ inhibited the HAO activity at three concentrations. In addition, HAO activity was activated by ethylenediaminetetraacetic acid at 0.4 mM, and a negative effect arose as the dose increased. The purified enzyme from Y1 is different from other reported HAOs. Further study should be conducted to investigate the enzyme.