Nitrogen Removal Performance of Novel Isolated Bacillus sp. Capable of Simultaneous Heterotrophic Nitrification and Aerobic Denitrification

Occurrence of dissimilatory nitrate reduction to ammonium (DNRA) in groundwater table fluctuation zones during dissolved organic nitrogen leaching through unsaturated zone

Nitrate reduction in unsaturated zone is critical for preventing groundwater contamination from anthropogenic nitrogen fertilization. Dissimilatory nitrate reduction to ammonium (DNRA), found in anoxic environments, offers an alternative pathway to denitrification by reducing nitrate while conserving nitrogen. However, the occurrence of DNRA in unsaturated zone remains poorly understood. To address this gap, we conducted numerical simulations to investigate the reactive transport of dissolved organic nitrogen (DON) through unsaturated zone under fluctuating groundwater table conditions, with the focus on the competition between denitrification and DNRA. Our results indicate that DNRA typically gets stronger within capillary fringe, with its intensity varying with groundwater table fluctuations. DNRA competes with denitrification, contributing up to 46.33 % of nitrate reduction, especially when groundwater table drops. The strength of DNRA requires comprehensive consideration of the adsorption characteristics, permeability and porosity of vadose zone, and in our study, silty clay loam-with the relatively weaker adsorptive capacity/lower permeability-exhibits the highest DNRA reaction rates and the largest reaction areas, while DNRA in sandy loam may occur during periods when both DON and NO3--N reserves are relatively low. This study firstly revealed the distribution of DNRA in groundwater table fluctuation zone, exploring its kinetics, controlling factors, and contributions, providing a scientific foundation for assessing the self-purification processes in groundwater contamination.

Influence of aquaculture practices on microbiota composition and pathogen abundance in pond ecosystems in South China

Pond microbiota play a crucial role in maintaining water quality and the health of aquaculture species. This study aimed to explore the relationship between pond water and sediment microbiota (especially potential pathogens) and physicochemical parameters under different aquaculture conditions. Samples of pond water and sediment were collected from 21 monitoring sites across eastern, western, and northern Guangdong, and the Pearl River Delta in November 2021, March 2022, and July 2022. Microbial structures were analyzed using high-throughput sequencing of the 16S rRNA gene. The results indicated that sediment microbiota distribution was more uniform than that of water microbiota. Additionally, sampling time significantly influenced the uniformity of water microbiota distribution more than that sediment microbiota. Factors such as aquaculture species, culture pattern, NH4 +-N, longitude, latitude, total nitrogen (TN), NO3 --N, NO2 --N, and total phosphorus (TP) were significantly correlated with water microbiota structure, and TN, TP, and organic carbon were significantly correlated with sediment microbiota structure. Furthermore, an increase in the NH4 +-N concentration in the pond water significantly increased the variety of pathogenic bacteria. Higher nitrogen levels also increased the relative abundance of Mycobacterium in pond water, whereas the culture pattern (freshwater, seawater, brackish, modern captive culture, freshwater factory container aquaculture, or seawater factory culture) and species significantly influenced the relative abundances of Vibrio, Tenacibaculum, Pseudoalteromonas, and Francisella. Additionally, the relative abundance of pathogenic bacteria in the sediment microbiota was significantly higher than that in the water microbiota. Our results suggest that the culture patterns, species, and nitrogen concentrations should be considered when preventing pathogenic bacteria growth in aquaculture waters.

The nitrogen removal characterization and ecological risk assessment of Bacillus sp. isolated from mariculture systems in China with spatiotemporal difference

The accumulation of nitrogen compounds may worsen the aquatic environment and cause serious economic losses in the aquaculture industry. In this study, the denitrification performance and ecological safety of 120 Bacillus sp. isolates with spatial and temporal differences were evaluated based on the aspects of hemolysis, drug resistance, denitrification performance, and purification effect for mariculture wastewater. Firstly, 55/120 safe strains with no hemolytic activity were detected through hemolysis testing. Then, based on selective denitrification medium and colorimetric reagent method, 34/55 Bacillus sp. with denitrification effect were screened. For these 34 Bacillus sp. isolates, the drug resistance phenotype and genotype, denitrification genes, and enzyme activities related to the nitrogen metabolizing (AMO, HAO, NAR, NIR) were examined. And the MARI was 0.00-0.25, with a multi-drug resistance rate of 17.6%. The drug resistance genes tetB, blaTEM, and cfr and the denitrification genes nap, nor, and narG were detected. Ultimately, 27/34 strains with denitrification function and ecological safety were obtained. In addition, eight Bacillus sp. showed certain denitrification effects on nitrogen-containing wastewater treatment. Among them, B. subtilis B24 has outstanding denitrification ability, with removal rates of 92%, 62%, 68%, and 30% for NH4 + -N, NO2--N, NO3--N, and TN in simulated wastewater, respectively. It also has a good denitrification effect in practical applications. This study provides candidate bacterial strains for the treatment of mariculture wastewater.

Optimal conditions and nitrogen removal performance of aerobic denitrifier Comamonas sp. pw-6 and its bioaugmented application in synthetic domestic wastewater treatment

To assess the possibility of using aerobic denitrification (AD) bacteria with high NO2--N accumulation for nitrogen removal in wastewater treatment, conditional optimization, as well as sole and mixed nitrogen source tests involving AD bacterium, Comamonas sp. pw-6 was performed. The results showed that the optimal carbon source, pH, C/N ratio, rotational speed, and salinity for this strain were determined to be succinate, 7, 20, 160 rpm, and 0%, respectively. Further, this strain preferentially utilized NH4+-N, NO3--N, and NO2--N, and when NO3--N was its sole nitrogen source, 92.28% of the NO3--N (150 mg·L-1) was converted to NO2--N. However, when NH4+-N and NO3--N constituted the mixed nitrogen source, NO3--N utilization by this strain was significantly lower (p < 0.05). Therefore, a strategy was proposed to combine pw-6 bacteria with traditional autotrophic nitrification to achieve the application of pw-6 bacteria in NH4+-N-containing wastewater treatment. Bioaugmented application experiments showed significantly higher NH4+-N removal (5.96 ± 0.94 mg·L-1·h-1) and lower NO3--N accumulation (2.52 ± 0.18 mg·L-1·h-1) rates (p < 0.05) than those observed for the control test. Thus, AD bacteria with high NO2--N accumulation can also be used for practical applications, providing a basis for expanding the selection range of AD strains for wastewater treatment.

Mechanisms of ammonia, calcium and heavy metal removal from nutrient-poor water by Acinetobacter calcoaceticus strain HM12

An Acinetobacter calcoaceticus strain HM12 capable of heterotrophic nitrification-aerobic denitrification (HN-AD) under nutrient-poor conditions was isolated, with an ammonia nitrogen (NH4+-N) removal efficiency of 98.53%. It can also remove heavy metals by microbial induced calcium precipitation (MICP) with a Ca2+ removal efficiency of 75.91%. Optimal conditions for HN-AD and mineralization of the strain were determined by kinetic analysis (pH = 7, C/N = 2.0, Ca2+ = 70.0 mg L-1, NH4+-N = 5.0 mg L-1). Growth curves and nitrogen balance elucidated nitrogen degradation pathways capable of converting NH4+-N to gaseous nitrogen. The analysis of the bioprecipitation showed that Zn2+ and Cd2+ were removed by the MICP process through co-precipitation and adsorption (maximum removal efficiencies of 93.39% and 80.70%, respectively), mainly ZnCO3, CdCO3, ZnHPO4, Zn3(PO4)2 and Cd3(PO4)2. Strain HM12 produces humic and fulvic acids to counteract the toxicity of pollutants, as well as aromatic proteins to increase extracellular polymers (EPS) and promote the biomineralization process. This study provides a experimental evidence for the simultaneous removal of multiple pollutants from nutrient-poor waters.

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.

Efficient nitrogen removal pathways and corresponding microbial evidence in tidal flow constructed wetlands for saline water treatment

The artificial tidal wetlands ecosystem was believed to be a useful device in treating saline water, and it played a significant part in global nitrogen cycles. However, limited information is available on nitrogen-cycling pathways and related contributions to nitrogen loss in tidal flow constructed wetlands (TF-CWs) for saline water treatment. This study operated seven experimental tidal flow constructed wetlands to remove nitrogen from saline water at salinities of 0-30‰. Stable and high NH4+-N removal efficiency (∼90.3%) was achieved, compared to 4.8-93.4% and 23.5-88.4% for nitrate and total nitrogen (TN), respectively. Microbial analyses revealed the simultaneous occurrence of anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA), nitrification and denitrification, contributing to nitrogen (N) loss from the mesocosms. The absolute abundances were 5.54 × 103-8.35 × 107 (nitrogen functional genes) and 5.21 × 107-7.99 × 109 copies/g (16S rRNA), while the related genera abundances ranged from 1.81% to 10.47% (nitrate reduction) and from 0.29% to 0.97% (nitrification), respectively. Quantitative response relationships showed ammonium transformation were controlled by nxrA, hzsB and amoA, and nitrate removal by nxrA, nosZ and narG. Collectively, TN transformation were determined by narG, nosZ, qnorB, nirS and hzsB through denitrification and anammox pathways. The proportion of nitrogen assimilation by plants was 6.9-23.4%. In summary, these findings would advance our understanding of quantitative molecular mechanisms in TF-CW mesocosms for treating nitrogen pollution that caused algal blooms in estuarine/coastal ecosystems worldwide.