Diverse metabolism drives comammox in continental-scale agricultural streams: Important ammonia oxidation but low N2O production.

Agriculture receives approximately 25 % of the annual global nitrogen input, 37 % of which subsequently runs off into adjacent low-order streams and surface water, where it may contribute to high nitrification and nitrous oxide (N2O). However, the mechanisms of nitrification and the pathways controlling N2O production in agricultural streams remain unknown. Here, we report that the third microbial ammonia oxidation process, complete ammonia oxidation (comammox), is widespread and contributes to important ammonia oxidation with low ammonia-N2O conversion in both basin- and continental-scale agricultural streams. The contribution of comammox to ammonia oxidation (21.5 ± 2.3 %) was between that of bacterial (68.6 ± 2.7 %) and archaeal (9.9 ± 1.8 %) ammonia oxidation. Interestingly, N2O production by comammox (18.5 ± 2.1 %) was higher than archaeal (10.5 ± 1.9 %) but significantly lower than bacterial (70.2 ± 2.6 %) ammonia oxidation. The first metagenome-assembled genome (MAG) of comammox bacteria from agricultural streams further revealed their potential extensive diverse and specific metabolism. Their wide habitats might be attributed to the diverse metabolism, i.e. harboring the functional gene of nitrate reduction to ammonia, while the lower N2O would be attributed to their lacking biological function to produce N2O. Our results highlight the importance of widespread comammox in agricultural streams, both for the fate of ammonia fertilizer and for climate change. However, it has not yet been routinely included in Earth system models and IPCC global assessments. Synopsis Widespread but overlooked comammox contributes to important ammonia oxidation but low N2O production, which were proved by the first comammox MAG found in agricultural streams.

Ammonium-derived nitrous oxide is a global source in streams.

Global riverine nitrous oxide (N2O) emissions have increased more than 4-fold in the last century. It has been estimated that the hyporheic zones in small streams alone may contribute approximately 85% of these N2O emissions. However, the mechanisms and pathways controlling hyporheic N2O production in stream ecosystems remain unknown. Here, we report that ammonia-derived pathways, rather than the nitrate-derived pathways, are the dominant hyporheic N2O sources (69.6 ± 2.1%) in agricultural streams around the world. The N2O fluxes are mainly in positive correlation with ammonia. The potential N2O metabolic pathways of metagenome-assembled genomes (MAGs) provides evidence that nitrifying bacteria contain greater abundances of N2O production-related genes than denitrifying bacteria. Taken together, this study highlights the importance of mitigating agriculturally derived ammonium in low-order agricultural streams in controlling N2O emissions. Global models of riverine ecosystems need to better represent ammonia-derived pathways for accurately estimating and predicting riverine N2O emissions.

Giant anterior scleral staphyloma caused by blunt ocular trauma: a case report.

BACKGROUND: Anterior scleral staphyloma is a relatively rare disease characterized by thinning and expansion of sclera. We described the clinical presentation, diagnosis and treatment of a case with giant anterior scleral staphyloma caused by blunt ocular trauma. CASE PRESENTATION: A 24-years-old male, presented with a black cyst-like mass protruding from the right eyeball for 9 years after a history of glass crush contusion. The ultrasound biomicroscopy examination showed two cysts in the right eyeball. The larger one was about 5.92 mm*4.69 mm in size and the scleral lacerations were connected to the posterior chamber below the cyst. For treatment, resection of the anterior scleral staphyloma and the scleral patch graft transplantation was performed. The vision of the patient was improved compared with that before surgery. There were no obvious complications. CONCLUSION: The clinical presentation, diagnosis, and treatment of the case with giant anterior scleral staphyloma can provide a reference for the management of anterior scleral staphyloma. Surgical resection and scleral patch graft should be a good option for the treatment of giant anterior scleral staphyloma.

Towards a more labor-saving way in microbial ammonium oxidation: A review on complete ammonia oxidization (comammox).

In the Anthropocene, nitrogen pollution is becoming an increasing challenge for both mankind and the Earth system. Microbial nitrogen cycling begins with aerobic nitrification, which is also the key rate-limiting step. For over a century, it has been accepted that nitrification occurs sequentially involving ammonia oxidation, which produces nitrite followed by nitrite oxidation, generating nitrate. This perception was changed by the discovery of comammox Nitrospira bacteria and their metabolic pathway. In addition, this also provided us with new knowledge concerning the complex nitrogen cycle network. In the comammox process, ammonia can be completely oxidized to nitrate in one cell via the subsequent activity of the enzyme complexes, ammonia monooxygenase, hydroxylamine dehydrogenase, and nitrite oxidodreductase. Over the past five years, research on comammox made great progress. However, there still exist a lot of questions, including how much does comammox contribute to nitrification? How large is the diversity and are there new strains to be discovered? Do comammox bacteria produce the greenhouse gas N2O, and how or to which extent may they contribute to global climate change? The above four aspects are of great significance on the farmland nitrogen management, aquatic environment restoration, and mitigation of global climate change. As large number of comammox bacteria and pathways have been detected in various terrestrial and aquatic ecosystems, indicating that the comammox process may exert an important role in the global nitrogen cycle.

Vasoactive agent buflomedil up-regulated expression of vascular endothelial growth factor in a rat model of sciatic nerve crush injury.

OBJECTIVES: To study the effect of Buflomedil on the morphological repair on crush injury of sciatic nerve and also the expression of vascular endothelial growth factor (VEGF). MATERIALS AND METHODS: Rat sciatic nerves were crushed by pincers. All of the 400 Sprague Dawley rats were randomly divided into: Sham-operated; saline; saline + VEGF-antibody; Buflomedil; and Buflomedil + VEGF antibody groups. The expression of VEGF in dorsal root ganglia (DRGs), following crush injury to sciatic nerves, was studied by RT-PCR, immunohistochemistry. The effects of Buflomedil on expression of VEGF and repair of neural pathology were also evaluated. RESULTS: VEGF mRNA was significantly increased in Buflomedil and Buflomedil + VEGF-antibody groups, compared with other groups. The number of VEGF-positive neurons was significantly increased in the Buflomedil and the saline groups. Besides, Buflomedil also caused less pathological changes in DRGs. CONCLUSIONS: The vasoactive agent Buflomedil may decrease the pathological lesion and improve the functional rehabilitation of peripheral nerves, which may correlate to upregulation of the expression of VEGF, following crush injury to the peripheral nerves.

Protective effects of the calcium-channel blocker flunarizine on crush injury of sciatic nerves in a rat model.

BACKGROUND: Neural damage can be mitigated by calcium-channel blockers (CCBs). However, the mechanism of action of CCBs is not yet fully understood. Objective : To investigate the mechanism of action and efficacy of CCB, flunarizine in restoring neural function after crush injury to the nerves. MATERIALS AND METHODS: The sciatic nerves of rats were crushed using pincers to establish the model for crush injury. Two hundred and eighty-eight Sprague-Dawley (SD) rats were randomly divided into sham-operated, saline, and low-dose flunarizine and high-dose flunarizine (FI and FII) groups. The expression of the protein c-fos in the dorsal root ganglia (DRG) after crush injury to the sciatic nerves was investigated by using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. The effect of flunarizine on c-fos expression and its efficacy in restoring neural function was evaluated. RESULTS: The c-fos messenger ribonucleic acid (mRNA) and protein expression in FI and FII groups was significantly lower than in the saline group and was the least in the FII group. Nerve-conduction velocity was increased in the order of: saline < FI< FII< sham-operated. There was no significant difference in the nerve-conduction velocity in the sham-operated and FII groups (P>.05). CONCLUSIONS: When administered after crush injury to peripheral nerves, flunarizine may protect neurons with lesions from further damage and improve neural function by downregulating c-fos expression.