Vertical profiles of water and sediment denitrifiers in two plateau freshwater lakes

Fe(II) enhances simultaneous phosphorus removal and denitrification in heterotrophic denitrification by chemical precipitation and stimulating denitrifiers activity

Using Fe(II) salt as the precipitant in heterotrophic denitrification achieves improved TP removal, and enhancement in denitrification was often observed. This study aimed to obtain a better understanding of Fe(II)-enhanced denitrification with sufficient carbon source supply. Laboratory-scale experiments were conducted in SBRs with or without Fe(II) addition. Remarkably improved TP removal was experienced. TP removal efficiency in Fe(II) adding reactor was 85.8 ± 3.4%; whereas, that in the reactor without Fe(II) addition was 31.1 ± 2.8%. Besides improved TP removal, better TN removal efficiency (94.1 ± 1.1%) were recorded when Fe(II) was added, and that in the reactor without Fe(II) addition was 89 ± 0.8%. The specific denitrification rate were observed increase by 12.6% when Fe(II) was added. Further microbial analyses revealed increases in the abundances of typical denitrifiers (i.e. Niastella, Opitutus, Dechloromonas, Ignavibacterium, Anaeromyxobacter, Pedosphaera, and Myxococcus). Their associated denitrifying genes, narG, nirS, norB, and nosZ, were observed had 14.2%, 19.4%, 21.6%, and 9.9% elevation, respectively. Such enhancement in denitrification shall not be due to nitrate-dependent ferrous oxidation, which prevails in organic-deficient environments. In an environment with a continuous supply of Fe(II) and plenty of carbon sources, a cycle of denitrifying enzyme activity enhancement in the presence of Fe(II) facilitating nitrogen substrate utilization, stimulating denitrifier metabolism and growth, elevating denitrifying genes abundance, and increasing denitrifying enzymes expression were thought to be responsible for the Fe(II)-enhanced heterotrophic denitrification. Fe(II) salt is often a less expensive precipitant and has recently become attractive for TP removal in wastewater. The findings of this study solidify previous observation of enhancement of both TP and TN removal by adding Fe(II) in denitrification, and would be helpful for developing cost-effective pollutant removal processes.

Long-term effects of decabromodiphenyl ether on denitrification in eutrophic lake sediments: Different sensitivity of six-type denitrifying bacteria

The widespread use of polybrominated diphenyl ethers inevitably results in their increased release into natural waters and subsequent deposition in sediments. However, their long-term effects on the bacteria participating in each step of denitrification in eutrophic lake sediments are still unknown. Here, we conducted a one-year microcosm experiment to determine the long-term effects of decabromodiphenyl ether (BDE-209), at low (2 mg kg^-1 dry weight) and high (20 mg kg^-1 dry weight) contamination levels, on six-type denitrifying bacteria and their activities in sediments collected from Taihu Lake, a typical eutrophic lake in China. At the end of the experiment, sediment denitrifying reductase activities were inhibited by BDE-209 at both levels, with the greatest inhibition seen for nitric oxide reductase activity. The higher nitrate concentration in the contaminated sediments was attributed to the inhibition of nitrate reductase activities. The abundances of six-type denitrifying genes (narG, napA, nirK, nirS, norB, and nosZ) significantly decreased under high BDE-209 treatment, and narG and napA genes were more sensitive to the toxicity of BDE-209. The results from pyrosequencing showed that BDE-209, at either treatment concentration, decreased the six-type denitrifying bacterial diversities and altered their community composition. This shift of six-type denitrifying bacterial communities might also be driven by the debrominated products concentrations of BDE-209 and variations in sediment inorganic nitrogen concentrations. In particular, some genera from phylum Proteobacteria such as Pseudomonas, Cupriavidus, and Azoarcus were decreased significantly because of BDE-209 and its debrominated products.

Community Composition and Spatial Distribution of N-Removing Microorganisms Optimized by Fe-Modified Biochar in a Constructed Wetland

Microbial nitrogen (N) removal capability can be significantly enhanced in a horizontal subsurface flow constructed wetland (HSCW) amended by Fe-modified biochar (FeB). To further explore the microbiological mechanism of FeB enhancing N removal, nirS- and nirK-denitrifier community diversities, as well as spatial distributions of denitrifiers and anaerobic ammonium oxidation (anammox) bacteria, were investigated in HSCWs (C-HSCW: without biochar and FeB; B-HSCW: amended by biochar; FeB-HSCW: amended by FeB) treating tailwater from a wastewater treatment plant, with C-HSCW without biochar and FeB and B-HSCW amended by biochar as control. The community structures of nirS- and nirK-denitrifiers in FeB-HSCW were significantly optimized for improved N removal compared with the two other HSCWs, although no significant differences in their richness and diversity were detected among the HSCWs. The spatial distributions of the relative abundance of genes involved in denitrification and anammox were more heterogeneous and complex in FeB-HSCW than those in other HSCWs. More and larger high-value patches were observed in FeB-HSCW. These revealed that FeB provides more appropriate habitats for N-removing microorganisms, which can prompt the bacteria to use the habitats more differentially, without competitive exclusion. Overall, the Fe-modified biochar enhancement of the microbial N-removal capability of HSCWs was a result of optimized microbial community structures, higher functional gene abundance, and improved spatial distribution of N-removing microorganisms.

Denitrifier communities differ in mangrove wetlands across China

To explore the geographical variations in the nosZ-denitrifier community and the underlying influential factors, surface sediments were collected from six mangroves across China, including Yunxiao (YX), Futian (FT), Fangchenggang (FCG), Zhanjiang (ZJ), Dongzhaigang (DZG), and Dongfang (DF). The nosZ gene abundance in mangrove sediments were 1.60 × 10⁵-1.17 × 10⁶ copies g^-1 dry sediment, with a higher density in Avicennia marina forest than the mudflat. Denitrifier community richness and diversity increased with decreasing latitude based on the Chao1 richness and Shannon diversity index, with the highest diversity being observed in the DF mangrove. The denitrifier communities could be classified into three groups including south DF mangrove, middle FCG, ZJ and DZG mangroves, and north YX and FT mangroves based on HCA and PCoA analysis. The nosZ OTUs could be divided into seven distinct clusters with different proportionality characteristics among mangroves. Environmental factors (TN, TOC, and salinity) collectively shape denitrifier communities in mangrove sediments.

Denitrification characterization of dissolved oxygen microprofiles in lake surface sediment through analyzing abundance, expression, community composition and enzymatic activities of denitrifier functional genes

The responses of denitrifiers and denitrification ability to dissolved oxygen (DO) concent in different layers of surface lake sediments are still poorly understood. Here, the optimal denitrification condition was constructed based on response surface methodology (RSM) to analyze the denitrification characteristics of surface sediments. The aerobic zone (AEZ), hypoxic zone (HYZ), up-anoxic zone (ANZ-1) and sub-anoxic zone (ANZ-2) were partitioned based on the oxygen contents, and sediments were collected using a customized-designed sub-millimeter scale sampling device. Integrated real-time quantitative PCR, Illumina Miseq-based sequencing and denitrifying enzyme activities analysis revealed that denitrification characteristics varied among different DO layers. Among the four layers, the DNA abundance and RNA expression levels of norB, nirS and nosZ were the highest at the aerobic layer, hypoxic layer and up-axoic layer, respectively. The hypoxia and up-anaerobic layer were the active nitrogen removal layers, since these two layers displayed the highest DNA abundance, RNA expression level and enzyme activities of denitrification functional genes. The abundance of major denitrifying bacteria showed significant differences among layers, with Azoarcus, Pseudogulbenkiania and Rhizobium identified as the main nirS, nirK and nosZ-based denitrifiers. Pearson’s correlation revealed that the response of denitrifiers to environmental factors differed greatly among DO layers. Furthermore, napA showed higher DNA abundance and RNA expression level in the aerobic and hypoxic layers than anaerobic layers, indicating that aerobic denitrifiers might play important roles at these layers.

Vertical distribution and assemblages of microbial communities and their potential effects on sulfur metabolism in a black-odor urban river

Black-odor phenomenon in highly urbanized river is increasingly recognized as a global ecological risk. Biotransformation associated with sulfur cycle is a major contributor to the blank-odor phenomenon. The vertical geochemical gradient in black-odor rivers is likely to alter microbial community assemblages and functions in the sulfur cycle. However, the interactions between geochemical gradients and microbial communities, as well as the changes in the process of sulfur biotransformation under different environmental conditions remain largely unknown. The vertical community assembly patterns and the impacts of microbial communities and genes on the biotransformation in the sulfur cycle were revealed in our study for the first time in a typical urban black-odor river, Jinchuan River, in China. Vertical beta-diversity patterns of microbial communities mainly resulted from species replacement that was largely driven by spatial turnover (β_SIM = 0.43) but also influenced by nestedness (β_NES = 0.08). MiSeq sequencing and GeoChip 5.0 microarray chip approaches were applied and identify 41 bacterial genera, 8 archaeal genera, and 26 genes involved in the sulfur cycle in Jinchuan River. The vertical beta-diversity patterns of microbial profile mainly resulted from species replacement. Those sulfur-related bacterial and archaeal genera, accounting for 23.15% and 42.65% of the total bacteria and archaea respectively in analysed samples, were mainly responsible for sulfur reduction. According to redundancy analysis, oxidation-reduction potential (r = -0.8662, P < 0.05), S^2- concentration (r = -0.6288, P < 0.05), and total nitrogen concentration (r = -0.6782, P < 0.05) were identified as factors that significantly affect sulfur-related microbial communities. The highest reaction potential was detected in the dissimilated sulfate reduction action and experienced an increase with depth increasing in the river system. The results indicated that the sulfur biotransformation in a deeper layer in river sediment could make more contribution to the black-odor phenomenon in urban rivers.

Denitrifier communities impacted by heavy metal contamination in freshwater sediment

Heavy metals are widely detected in natural environments, however their impacts on denitrifier community in freshwater ecosystem remain unclear. The present study investigated the changes of denitrifier communities (based on nosZ (nitrous oxide reductase) gene) in a freshwater reservoir contaminated by a severe accidental spill of heavy metals. The abundance of nosZ-denitrifiers drastically decreased, and their community richness, diversity and structure also showed considerable variations. The mainly detected denitrifying bacteria included Pseudogulbenkiania, Pseudomonas and two unknown groups. These major nosZ-denitrifier groups responded in different ways to heavy metal pollution. Metal contamination could exert a profound influence on denitrifier community in freshwater sediment. This work could provide some new insights to the impact of metal pollution on nitrogen cycling.

Multi-scale factors affecting composition, diversity, and abundance of sediment denitrifying microorganisms in Yangtze lakes

Sediment denitrification is the dominant nitrogen removal pathway in many aquatic habitats and can be regulated by local-, landscape-, and regional-scale factors. However, the mechanisms for how these multiple scale factors and their interactions affect the sediment denitrifying communities remain poorly understood. In this study, we investigated the community composition, diversity, and abundance of nitrite reductase genes (nirK and nirS)-encoding denitrifiers in 74 sediment samples from 22 Yangtze lakes using clone library and quantitative PCR techniques. Information of location, climate, catchment land use, water quality, sediment properties, and plant communities at each sampling site was analyzed to elucidate the effects of regional, landscape, and local factors on the characteristics of sediment denitrifying communities. Results of canonical correspondence analysis indicated that local factors were the key determinants of denitrifying community composition, accounting for over 20% of the total variation. Additionally, certain regional and landscape factors, including elevation and catchment built-up land, were also significantly related to the composition of denitrifying communities. Variance partitioning analyses revealed that diversity and abundance in the nirK denitrifier community were largely influenced by local factors, while those in the nirS community were controlled by both local and regional factors. Our findings highlight the importance of using different scale factors to explain adequately the composition and structure of denitrifying communities in aquatic environments.