Corpse decomposition increases nitrogen pollution and alters the succession of nirK-type denitrifying communities in different water types

Biotic regulation of phoD-encoding gene bacteria on organic phosphorus mineralization in lacustrine sediments with distinct trophic levels

Organic phosphorus (Po) mineralization hydrolyzed by alkaline phosphatase (APase) can replenish bioavailable P load in the sediment water ecosystem of lakes. However, the understanding about the interaction between P load and bacteria community encoding APase generation in the sediment are still limited. Different P pools in the sediments from Taihu Lake, China were measured using sequential extraction procedure. The APAase activity (APA) were obtained accompanying with enzymatic dynamical parameters Vmax and Km. The abundances and diversity of gene phoD-harboring bacterial communities were assessed using high throughput sequencing. The analysis results showed the decrease of potentially bioavailable P fractions including MgCl2-P and Fe-P along sampling gradient southwards together with active P concentrations in the water. Conversely, increasing APA and absolute abundance of phoD gene were found with the decreasing of P loads southwards. Positive correlation (p < 0.05) between absolute abundance and APA indicated that phoD-encoding bacteria manipulated the APA and Po mineralization. Negative correlation (p < 0.01) suggested that the APA was restrained by high P load and was promoted under low P condition. However, higher Vmax and Km values suggested that high mineralization potential of Po maintained the high concentrations of potentially bioavailable P even the APA was restricted. The abundance increase of predominant genus Cobetia (from 15.51 to 24.34 %) mirrored by the reduced Calothrix abundance (from 24.65 to 1036 %) was speculated to be responsible for the APA promotion under low P condition. Higher diversity indices in the high P scenario suggested that high P load stimulated the ecological diversity of gene phoD-encoding bacteria community. Generally, rare taxa such as Burkholderia having high connected degrees in bacterial communities together with abundant genera synergistically manipulated the phoD gene abundance and APase generation. Interaction between P fractions and bacteria encoding phoD gene determined the eutrophication status in the lacustrine ecosystem.

Carrion ecology in inland aquatic ecosystems: a systematic review

Carrion ecology, i.e. the decomposition and recycling of dead animals, has traditionally been neglected as a key process in ecosystem functioning. Similarly, despite the large threats that inland aquatic ecosystems (hereafter, aquatic ecosystems) face, the scientific literature is still largely biased towards terrestrial ecosystems. However, there has been an increasing number of studies on carrion ecology in aquatic ecosystems in the last two decades, highlighting their key role in nutrient recirculation and disease control. Thus, a global assessment of the ecological role of scavengers and carrion in aquatic ecosystems is timely. Here, we systematically reviewed scientific articles on carrion ecology in aquatic ecosystems to describe current knowledge, identify research gaps, and promote future studies that will deepen our understanding in this field. We found 206 relevant studies, which were highly biased towards North America, especially in lotic ecosystems, covering short time periods, and overlooking seasonality, a crucial factor in scavenging dynamics. Despite the low number of studies on scavenger assemblages, we recorded 55 orders of invertebrates from 179 families, with Diptera and Coleoptera being the most frequent orders. For vertebrates, we recorded 114 species from 40 families, with birds and mammals being the most common. Our results emphasise the significance of scavengers in stabilising food webs and facilitating nutrient cycling within aquatic ecosystems. Studies were strongly biased towards the assessment of the ecosystem effects of carrion, particularly of salmon carcasses in North America. The second most common research topic was the foraging ecology of vertebrates, which was mostly evaluated through sporadic observations of carrion in the diet. Articles assessing scavenger assemblages were scarce, and only a limited number of these studies evaluated carrion consumption patterns, which serve as a proxy for the role of scavengers in the ecosystem. The ecological functions performed by carrion and scavengers in aquatic ecosystems were diverse. The main ecological functions were carrion as food source and the role of scavengers in nutrient cycling, which appeared in 52.4% (N = 108) and 46.1% (N = 95) of publications, respectively. Ecosystem threats associated with carrion ecology were also identified, the most common being water eutrophication and carrion as source of pathogens (2.4%; N = 5 each). Regarding the effects of carrion on ecosystems, we found studies spanning all ecosystem components (N = 85), from soil or the water column to terrestrial vertebrates, with a particular focus on aquatic invertebrates and fish. Most of these articles found positive effects of carrion on ecosystems (e.g. higher species richness, abundance or fitness; 84.7%; N = 72), while a minority found negative effects, changes in community composition, or even no effects. Enhancing our understanding of scavengers and carrion in aquatic ecosystems is crucial to assessing their current and future roles amidst global change, mainly for water-land nutrient transport, due to changes in the amount and speed of nutrient movement, and for disease control and impact mitigation, due to the predicted increase in occurrence and magnitude of mortality events in aquatic ecosystems.

Cadaverine and putrescine exposure influence carbon and nitrogen cycling genes in water and sediment of the Yellow River

The response patterns of microbial functional genes involved in biogeochemical cycles to cadaver decay is a central topic of recent environmental sciences. However, the response mechanisms and pathways of the functional genes associated with the carbon (C) and nitrogen (N) cycling to cadaveric substances such as cadaverine and putrescine remain unclear. This study explored the variation of functional genes associated with C fixation, C degradation and N cycling and their influencing factors under cadaverine, putrescine and mixed treatments. Our results showed only putrescine significantly increased the alpha diversity of C fixation genes, while reducing the alpha diversity of N cycling genes in sediment. For the C cycling, the mixed treatment significantly decreased the total abundance of reductive acetyl-CoA pathway genes (i.e., acsB and acsE) and lig gene linked to lignin degradation in water, while only significantly increasing the hydroxypropionate-hydroxybutylate cycle (i.e., accA) gene abundance in sediment. For the N cycling, mixed treatment significantly decreased the abundance of the nitrification (i.e., amoB), denitrification (i.e., nirS3) genes in water and the assimilation pathway gene (i.e., gdhA) in sediment. Environmental factors (i.e., total carbon and total nitrogen) were all negatively associated with the genes of C and N cycling. Therefore, cadaverine and putrescine exposure may inhibit the pathway in C fixation and N cycling, while promoting C degradation. These findings can offer some new insight for the management of amine pollution caused by animal cadavers.

Arbuscular mycorrhizal fungi reduce soil N2O emissions by altering root traits and soil denitrifier community composition

Arbuscular mycorrhizal fungi (AMF) increase the ability of plants to obtain nitrogen (N) from the soil, and thus can affect emissions of nitrous oxide (N2O), a long-lived potent greenhouse gas. However, the mechanisms underlying the effects of AMF on N2O emissions are still poorly understood, particularly in agroecosystems with different forms of N fertilizer inputs. Utilizing a mesocosm experiment in field, we examined the effects of AMF on N2O emissions via their influence on maize root traits and denitrifying microorganisms under ammonia and nitrate fertilizer input using 15N isotope tracer. Here we show that the presence of AMF alone or both maize roots and AMF increased maize biomass and their 15N uptake, root length, root surface area, and root volume, but led to a reduction in N2O emissions under both N input forms. Random forest model showed that root length and surface area were the most important predictors of N2O emissions. Additionally, the presence of AMF reduced the (nirK + nirS)/nosZ ratio by increasing the relative abundance of nirS-Bradyrhizobium and Rubrivivax with ammonia input, but reducing nosZ-Azospirillum, Cupriavidus and Rhodopseudomonas under both fertilizer input. Further, N2O emissions were significantly and positively correlated with the nosZ-type Azospirillum, Cupriavidus and Rhodopseudomonas, but negatively correlated with the nirS-type Bradyrhizobium and Rubrivivax. These results indicate that AMF reduce N2O emissions by increasing root length to explore N nutrients and altering the community composition of denitrifiers, suggesting that effective management of N fertilizer forms interacting with the rhizosphere microbiome may help mitigate N2O emissions under future N input scenarios.

Metagenomics reveals the self-recovery and risk of antibiotic resistomes during carcass decomposition of wild mammals

Animal carcass decomposition may bring serious harm to the environment, including pathogenic viruses, toxic gases and metabolites, and antibiotic resistance genes (ARGs). However, how wild mammal corpses decomposition influence and change ARGs in the environment has less explored. Through metagenomics, 16S rRNA gene sequencing, and physicochemical analysis, this study explored the succession patterns, influencing factors, and assembly process of ARGs and mobile genetic elements (MGEs) in gravesoil during long-term corpse decomposition of wild mammals. Our results indicate that the ARG and MGE communities related to wildlife corpses exhibited a pattern of differentiation first and then convergence. Different from the farmed animals, the decomposition of wild animals first reduced the diversity of ARGs and MGEs, and then recovered to a level similar to that of the control group (untreated soil). ARGs and MGEs of the gravesoil are mainly affected by deterministic processes in different stages. MGEs and bacterial community are the two most important factors affecting ARGs in gravesoil. It is worth noting that the decomposition of wild animal carcasses enriched different high-risk ARGs at different stages (bacA, mecA and floR), which have co-occurrence patterns with opportunistic pathogens (Comamonas and Acinetobacter), thereby posing a great threat to public health. These results are of great significance for wildlife corpse management and environmental and ecological safety.

Metagenomics reveals elevated temperature causes nitrogen accumulation mainly by inhibiting nitrate reduction process in polluted water

Determining the response of functional genes and microbiota involved in the nitrogen (N) cycle to warming in the face of global climate change is a hotpot topic. However, whether and how elevated temperature affects the N-cycle genes in polluted water remains unclear. Based on metagenomics, we investigated the responses of the whole N-cycling genes and their microbial communities to the temperature gradients (23, 26, 29, 32, and 35 °C) using animal cadavers as an N-pollution model. We found that the abundance of gene families involved in glutamate metabolism, assimilatory nitrate reduction to nitrite (ANRN), and denitrification pathways decreased with temperature. Moreover, warming reduced the diversity of N-cycling microbial communities. Ecological network analysis indicated that elevated temperature intensified the mutual competition of N-cycle genes. The partial least squares path model (PLS-PM) showed that warming directly suppressed most N-cycle pathways, especially glutamate metabolism, denitrification, and ANRN pathways. Corpse decay also indirectly inhibited N-cycling via regulating N content and microbial communities. Our results highlight warming leads to N accumulation by inhibiting the ANRN and denitrification pathways, which may jeopardize ecological environment security. Our study is expected to provide valuable insights into the complex N-cycle process and N-pollution in warmer aquatic ecosystems.

Microencapsulated reactor for simultaneous removal of calcium, fluoride and phenol using microbially induced calcium precipitation: Mechanism and functional characterization

Fluoride ions (F^-) and phenol in groundwater have become a great hurdle to the pursuit of a healthy drinking water source. This study established a microencapsulated immobilization reactor with Aquabacterium sp. CZ3 for the simultaneous removal of nitrate (NO₃^--N), calcium (Ca²⁺), F^-, and phenol from groundwater with 100%, 67.84%, 88.67%, and 100% removal efficiencies, respectively. The three-dimensional mesh structure of microcapsules facilitated the transport and metabolism of substances, while their synergistic effect with bacteria promoted the removal of contaminants. F^- was removed by co-precipitation to generate Ca₅(PO₄)₃F and CaF₂ and adsorption. On one hand, the phenol toxicity promoted the production of extracellular polymers and improved the tolerance of bacteria; on the other hand, the degradation of phenol provided a carbon source for bacteria and promoted the denitrification. The development of microencapsulated immobilized reactor provided a clear mechanism for phenol and F^- removal under the microbially induced calcium precipitation (MICP) technique, while providing a valuable solution for the treatment of complex groundwater resources.

Dissecting the microbial community structure of internal organs during the early postmortem period in a murine corpse model

BACKGROUND

Microorganisms distribute and proliferate both inside and outside the body, which are the main mediators of decomposition after death. However, limited information is available on the postmortem microbiota changes of extraintestinal body sites in the early decomposition stage of mammalian corpses.

RESULTS

This study investigated microbial composition variations among different organs and the relationship between microbial communities and time since death over 1 day of decomposition in male C57BL/6 J mice by 16S rRNA sequencing. During 1 day of decomposition, Agrobacterium, Prevotella, Bacillus, and Turicibacter were regarded as time-relevant genera in internal organs at different timepoints. Pathways associated with lipid, amino acid, carbohydrate and terpenoid and polyketide metabolism were significantly enriched at 8 h than that at 0.5 or 4 h. The microbiome compositions and postmortem metabolic pathways differed by time since death, and more importantly, these alterations were organ specific.

CONCLUSION

The dominant microbes differed by organ, while they tended toward similarity as decomposition progressed. The observed thanatomicrobiome variation by body site provides new knowledge into decomposition ecology and forensic microbiology. Additionally, the microbes detected at 0.5 h in internal organs may inform a new direction for organ transplantation.

Study and Application of Urban Aquatic Ecosystem Health Evaluation Index System in River Network Plain Area

The evaluation index system of urban aquatic ecosystem health is of great significance for the assessment and management of urban river networks, and for urban development planning. In this paper, the concept of urban aquatic ecosystem health was analyzed by the relationship between human, city and aquatic ecosystem, and its evaluation index system was established from environmental conditions, ecological construction, and social service. In addition, the weight value of each index was calculated by the analytic hierarchy process, and the grading standard of each index was set. Jiading New City, a typical city of the river network plain area in Yangtze River delta, was selected as the aquatic ecosystem health evaluation sample. The fuzzy comprehensive method was used to evaluate the aquatic ecosystem health of Jiading New City. The results indicated that the water ecosystem health of Jiading New City reached the "good" level. For the criterion level, environmental conditions and ecological construction reached the "good" level, and social services reached the "excellent" level. For the indicator level, most indicators reached "good" and "excellent" levels, but the river complexity and benthic macroinvertebrate diversity are still in the "poor" state, which indicates that the aquatic environment has greatly improved, but the aquatic ecosystem has not been fully restored. Results suggested that river complexity and biodiversity should be increased in urban construction planning. The evaluation index system established in this paper can be used to reflect the urban aquatic ecosystem health conditions in river network plain areas.

Heavy rainfall accelerates the temporal turnover but decreases the deterministic processes of buried gravesoil bacterial communities

The influences of global climatic change require an understanding of changes in soil microbial communities under precipitation. However, little is known about how soil ("gravesoil") microbial communities associated with corpse decay respond to precipitation. Here, we explored the variations of temporal turnover and assembly in gravesoil bacterial communities in the Qinghai-Tibet Plateau ecosystem via controlled rainfall simulation experiments. In our experiments, rainfall intensity was set to 2.5 and 5 mm/3 days to simulate moderate and heavy rainfall, respectively, and sampling was conducted on the 4th, 11th, 18th, 32nd, 46th and 60th day. Our results showed precipitation significantly altered bacterial abundances and community structures. Analysis of time-decay relationships revealed that precipitation resulted in a divergent succession of gravesoil bacterial community structure and abundance changes of dominant phyla, such as Chloroflexi. Moreover, in the experimental groups, our results suggested that moderate rainfall increased the deterministic processes in the initial and mid periods, whereas heavy rainfall decreased these processes of gravesoil microbial community assembly in every period compared with those in the control group. The dispersal capacity induced by stochastic processes of gravesoil microbial communities decreased over time under moderate rainfall, whereas it initially increased and then decreased under heavy rainfall. This study highlights the influence of heavy rainfall on bacterial communities during corpse decay, which can provide some inferences for predicting changes in soil microbial communities under global climatic change.

Corpse decay of wild animals leads to the divergent succession of nrfA-type microbial communities

Animal carcasses introduce large amounts of nitrates and ammonium into the soil ecosystem. Some of this ammonium is transformed from nitrite through the nrfA-type microbial community. However, it is unclear how nrfA-type microorganisms respond to the decomposition of corpses. This study applied high-throughput sequencing to characterize the ecological succession of nrfA-type microbial communities in grassland soil. Our results showed that Cyclobacterium and Trueperella were the predominant genera for nrfA-type communities in soil with a decomposing corpse (experimental group), while Cyclobacterium and Archangium were dominant in soil without a corpse (control group). The alpha diversity indexes and the resistance and resilience indexes of the microbial communities initially increased and then decreased during decomposition. Compared with the control group, nrfA-encoding community structure in the experimental group gradually became divergent with succession and temporal turnover accelerated. Network analysis revealed that the microbial communities of the experimental group had more complex interactions than those of the control groups. Moreover, the bacterial community assembly in the experimental group was governed by stochastic processes, and the communities of the experimental group had a weaker dispersal capacity than those of the control group. Our results reveal the succession patterns of the nrfA-type microbial communities during degradation of wild animal corpses, which can offer references for demonstrating the ecological mechanism underlying the changes in the nrfA-type microbial community during carcass decay. KEY POINTS: • Corpse decay accelerates the temporal turnover of the nrfA-type community in soil. • Corpse decay changes the ecological succession of the nrfA-type community in soil. • Corpse decay leads to a complex co-occurrence pattern of the nrfA-type community in soil.

A review on nirS-type and nirK-type denitrifiers via a scientometric approach coupled with case studies

The denitrification process plays an important role in improving water quality and is a source/sink of nitrous oxide to the atmosphere. The second important rate-limiting step of the denitrification process is catalyzed by two enzymes with different structures and unrelated evolutionary relationships, namely, the Cu-type nitrite reductase encoded by the nirK gene and the cytochrome cd1-type nitrite reductase encoded by the nirS gene. Although some relevant reviews have been published on denitrifiers, most of these reviews do not include statistical analysis, and do not compare the nirS and nirK communities in-depth. However, a systematic study of the nirS-type and nirK-type denitrifying communities and their response to environmental factors in different ecosystems is needed. In this review, a scientometric approach combined with case studies was used to study the nirS-type and nirK-type denitrifiers. The scientometric approach demonstrated that Pseudomonas, Paracoccus, and Thauera are the most frequently mentioned nirS-type denitrifiers, while Pseudomonas and Bradyrhizobium are the top two most frequently mentioned nirK-type denitrifiers. Among various environmental factors, the concentrations of nitrite, nitrate and carbon sources were widely reported factors that can influence the abundance and structure of nirS-type and nirK-type denitrifying communities. Case studies indicated that Bradyrhizobium was the major genus detected by high-throughput sequencing in both nirS and nirK-type denitrifiers in soil systems. nirS-type denitrifiers are more sensitive to the soil type, soil moisture, pH, and rhizosphere effect than nirK. To clarify the relationships between denitrifying communities and environmental factors, the DNA stable isotope probe combined with metagenomic sequencing is needed for new denitrifier detections.

Carcass decay deteriorates water quality and modifies the nirS denitrifying communities in different degradation stages

Corpse degradation may release amounts of hazardous materials (e.g., cadaverine, putrescine and ammonia) into surrounding areas, which deteriorate environments and result in nitrogen contamination. Nitrate or nitrite can be reduced to nitrogen gas by denitrifying bacteria, thus alleviating nitrogen contamination and purifying aquatic environments. However, the reaction of nirS-encoding denitrifiers to carcass degradation is less studied. Therefore, water physiochemical analysis and high-throughput sequencing were applied to explore the successional pattern of nirS denitrifying communities in the Yellow River water and tap water during three stages of animal cadaver decay (submerged fresh, advanced floating decay as well as sunken remains) and relevant control group. Nitrate nitrogen (NO₃-N) and ammonia nitrogen (NH₄⁺-N) concentration in corpse groups were highly elevated compared with control groups. The dominant phylum for nirS denitrifying communities was Proteobacteria. Abundant denitrifying genera Paracoccus, Alicycliphilus and Diaphorobacter were detected, and these genera have been reported to participate in the degradation of organic pollutants. Particularly, nirS-type community structures were remarkably influenced by corpse decay and became similar with succession. Water total dissolved solids (TDS), salinity, conductivity (CON) and phosphate were primary impacting factors driving the community structures, but the effect of water type was almost negligible. Notably, denitrifying community assembly was dominated by deterministic processes rather than stochastic processes, and the relative importance of deterministic processes among most corpse groups was higher than that in control groups, indicating that environmental filtering regulates the denitrifying communities. Our results provide new insight into environmental purification for hazardous materials produced by corpse degradation, thereby providing valuable advice to environmental administration.

Effects of copper and florfenicol on nirS- and nirK-type denitrifier communities and related antibiotic resistance in vegetable soils

Denitrification play an important role in nitrogen cycle and is affected by veterinary drugs entering agricultural soils. In the present study, the effects of copper and florfenicol on denitrification, related antibiotic resistance and environmental variables were characterized using real-time quantitative PCR (qPCR) and amplicon sequencing in a short-term (30 d) soil model experiment. Drug additions significantly decreased the nirS gene abundance (P < 0.05) but maximized the abundance of gene nirK in soil containing florfenicol and moderate copper levels (150 mg kg^-1). Surprisingly, copper additions decreased the fexB gene abundance, however, the abundance of gene pcoD significantly increased in soils containing florfenicol, moderate copper levels (150 mg kg^-1), and florfenicol and low copper levels (30 mg kg^-1), respectively (P < 0.05). Overall, the nirK-type community composition was more complex than that of nirS-type but Proteobacteria predominated (> 90%) in both communities. Correlation analysis indicated that the gene abundance of fexB was highly correlated with NH₄⁺-N (P < 0.05) and NO₃^--N (P < -0.01), and floR gene abundance was positively correlated with nirK (P < 0.01). Besides, the abundance of nirS-type genera Bradyrhizobium and Pseudomonas were obviously related to total organic matter (TOM), total nitrogen (TN) or total phosphorus (TP) (P < 0.05), while the abundance of nirK-type Rhizobium, Sphingomonas and Bosea showed a significantly correlated with TOM, TN or copper contents (P < 0.05). Taken together, copper and florfenicol contamination increased the possibility of durg resistance genes spread in agricultural soils through nitrogen transformation.