D-amino acids (DAAs), once considered minor enantiomers, are now recognised as abundant and dynamic components of marine and terrestrial organic matter. While they do not participate in ribosomal protein synthesis, they play crucial roles in microbial physiology, particularly in bacterial cell wall structure. This review systematically synthesises the current understanding of DAA sources, distribution and fate, with a central focus on the microbial catabolic pathways that drive their recycling in marine and terrestrial environments. We show that, despite differences in DAA distribution and bioavailability between marine and terrestrial ecosystems, the core catabolic strategies adopted by bacteria-conversion to α-keto acids, L-amino acids (LAAs) or Gly-are largely conserved. We also evaluate limitations in current studies and major knowledge gaps, including the unclear role of marine fungi in DAA turnover and the relative lack of systematic studies on DAA-catabolising taxa and pathways in terrestrial microbial communities. This review highlights the ecological significance of microbial-mediated DAA recycling in marine and terrestrial environments, offering a better understanding of the global biogeochemical cycling of DAAs.

Nitrous acid (HONO) is a key precursor to hydroxyl radicals (OH) and a reservoir of reactive nitrogen. Here, we identify abiotic photodecomposition of marine algae as a previously unrecognized HONO source. During Ulva prolifera green tides, daytime HONO levels closely followed tidal cycles, peaking at low tide, contrasting with typical inland nocturnal peaks. Chamber experiments confirm that common algae (e.g., U. prolifera and Sargassum) emit HONO under irradiation, with fluxes increasing with light intensity and algal surface area. This light-driven, abiotic process is mechanistically distinct from microbial soil HONO production. Measured fluxes (1.08 × 10-7 to 2.31 × 10-6 mole per square meter per hour) are comparable to soil HONO emissions and exceed marine NO fluxes by two to three orders of magnitude. Incorporating this source into atmospheric models substantially elevated HONO concentrations, enhancing OH and ozone production and oxidation of climate-relevant gases. With intensifying global algal blooms driven by eutrophication and climate warming, this process is expected to become increasingly important.

α-Amylases (EC 3.2.1.1) are among the most important industrial enzymes in starch saccharification, detergent, paper, and textile industries. Canonical α-amylases typically contain Ca2+ in their structure, which is not directly involved in catalysis but essential in maintaining the structural integrity of α-amylases. Ca2+ ions are easily removed by chelating reagents, which may affect the activity and stability of α-amylases and thereby hinder their applications in some industries. Here, we identified a metal-free α-amylase, AmyY, from the bacterium Alkalimonas sp. NCh-2 isolated from an alkaline hot spring. AmyY contains a catalytic module of glycoside hydrolase family 13 (GH13) and a carbohydrate-binding module of family 20 (CBM20). AmyY exhibits high activity under alkaline conditions (pH 8.0-11.0) and tolerance to high salinity, chelating reagents, and surfactants. We solved the structures of AmyY and its complex with acarbose. Although the overall topology and active sites of AmyY resemble those of reported GH13 α-amylases, the structure of AmyY is devoid of metal ions. The inability of AmyY to bind metal ions results from replacements of acidic amino acid residues by neutral ones. Combined with biochemical, structural, and bioinformatic data, we demonstrated that AmyY and its homologs represent a class of metal-free α-amylases in GH13. Moreover, structural analyses revealed that the CBM20 of AmyY is highly flexible, and we obtained a mutant with enhanced thermostability by truncating the CBM20. This mutant demonstrates remarkable wash performance and desizing capability at alkaline pH, which underscores its application potential in the detergent and textile industries.IMPORTANCEWhile canonical GH13 α-amylases typically contain Ca2+, our biochemical and structural data reveal that AmyY has evolved a metal-free architecture. This is achieved through the replacement of acidic metal-coordinating residues by neutral ones, abolishing metal binding without compromising catalytic efficiency. This work expands the structural and functional diversity of GH13 by defining a class of metal-free α-amylases, with AmyY and its homologs as representatives. Furthermore, the engineered AmyY with enhanced thermostability offers a candidate biocatalyst for industrial applications, such as the detergent industry. The structure of AmyY also offers a blueprint for engineering other α-amylases into metal-independent forms.

Alginate is an important component of the cell wall of brown algae and is mainly utilized by bacteria in the oceans. Although many marine Vibrio strains are known alginate utilizers, their mechanisms for alginate utilization have not been fully understood. Here, we investigated the alginate utilization pathway of the marine bacterium Vibrio sp. C42, an alginate lyase-excreting strain collected from the surface of Sargassum. Based on genomic, transcriptomic, and proteomic analyses, an alginate utilization locus (AUL) responsible for alginate utilization was identified in Vibrio sp. C42. In the alginate utilization pathway, eight extracellular alginate lyases break down alginate into oligosaccharides. These oligosaccharides are then internalized through an outer membrane porin and two inner membrane transporters: sodium-solute symporter (SSS) and tripartite tricarboxylate transporter (TTT). Biochemical and structural analyses demonstrated that the TTT is novel and specific to alginate oligosaccharides. Moreover, bioinformatic analysis suggests that TTT is widely involved in alginate utilization of marine bacteria. These findings reveal a new TTT-involved alginate utilization pathway in marine Vibrio and other bacteria, shedding light on alginate metabolism in the sea. IMPORTANCE:Due to the huge quantity of brown algae in global oceans, alginate is an important organic carbon source in marine ecosystems. Alginate is utilized mainly by bacteria, becoming an important component of marine carbon cycling. Marine Vibrio strains play an important role in marine alginate utilization. Here, we reveal a novel TTT (tripartite tricarboxylate transporter) involved in the alginate utilization pathway in marine Vibrio sp. C42. Moreover, the TTT was identified as a novel protein specific to the transport of alginate oligosaccharides. Bioinformatic analysis further indicated its universality in the AULs of marine Vibrio and other bacteria, suggesting that TTT is widely involved in alginate utilization by marine bacteria. Therefore, this TTT-dependent alginate utilization pathway may have significance in marine alginate metabolism and cycling.

Inhibiting dipeptidyl peptidase-IV (DPP-IV) activity is an effective approach for the treatment of type 2 diabetes. Proteases that specifically cleave the Y-Gly bonds in collagen Gly-X(Pro)-Y repeats could produce peptides featuring a Pro at the penultimate of N-termini, which are regarded as potential dipeptidyl-peptidase IV inhibitory peptides (DPP-IV-IPs). However, few proteases so far applied in preparing DPP-IV-IPs exhibited this character. Here, an S8 family collagenolytic protease A4095 with Y-Gly bond preference was used to prepare fish skin collagen hydrolysate with high DPP-IV inhibitory potency. A total of 377 peptides were identified by LC-MS/MS and 13 potential DPP-IV-IPs were screened and synthesized. Seven peptides were found to possess DPP-IV inhibitory activity for the first time and determined as competitive inhibitors of DPP-IV. Especially, the peptide GPRGLP showed the highest DPP-IV inhibitory activity with IC50 of 63.87 ± 3.36 μM. Its inhibitory activity decreased after gastric digestion but remained stable during intestinal digestion. The molecular docking and molecular dynamic simulation revealed that the activity of these DPP-IV-IPs attributed to the hydrogen bonds or hydrophobic interactions formed by their N-terminal amino acids with DPP-IV. This study demonstrated that protease A4095 is an efficient tool enzyme for generating novel DPP-IV-IPs from collagen, which have potentials in functional foods and anti-diabetic drugs.

Global surface ozone (O3), intensified by climate change, poses increasing health and ecosystem threats. Despite stringent air policies, China's persistent O3 pollution exemplifies a global challenge intertwined with climate actions reshaping emission pathways. Optimal mitigation remains contentious, primarily due to inconsistent conclusions regarding the sensitivity of summer regional O3 formation. Here we show the path dependency in O3 mitigation strategies for synergistic clean air and climate action goal achievement over multidecade scales. This path dependence is validated by observed concurrent plateaus (2020-2023) in deweathered O3 concentrations and sensitivity trends across Chinese megacity clusters. Leveraging this understanding of path dependency, we quantitatively reveal that the optimal future strategy involves prioritizing early volatile organic compound reductions, as their high effectiveness for regional O3 mitigation gradually diminishes towards 2050. This challenges prevailing nitrogen oxides priority paradigms. Our work reframes O3 control, providing a paradigm for resilient air quality-climate governance.

Free trans-4-hydroxy-L-proline (T4LHyp), primarily released during the natural degradation of collagen, is absorbed and catabolised by heterotrophic bacteria, contributing to the global recycling of carbon and nitrogen. While bacterial T4LHyp catabolism is well documented, our understanding on how bacteria recognize and import T4LHyp remains limited. Here we show that HatA, the substrate binding protein (SBP) of an ATP-binding cassette transporter within the T4LHyp gene cluster of Vibrio alginolyticus 1A11092, recognizes T4LHyp during its uptake by the strain. HatA possessed significant binding affinity towards T4LHyp and L-proline and a binding signature (W33F37D86V135F240R243Y265N267Y303), acting as the structural determinant for the specific ligand recognition, was defined. This signature is strictly conserved among HatA and its homologs, representing a subgroup of cluster D-II of SBPs. Genes encoding HatA-like SBPs are often located adjacent to collagenase and T4LHyp catabolic enzyme genes, and are nearly exclusively found in the genomes of Vibrio spp. in hosts and marine environments, which helps them exert pathogenicity when encountering host or environmental collagen. This study reveals a T4LHyp SBP in cosmopolitan Vibrio spp., offering better insights into the global T4LHyp catabolism and recycling driven by bacteria. This study reveals the structural determinants of trans-4-hydroxy-L-proline (T4LHyp) recognition by a substrate binding protein HatA in heterotrophic bacteria. Uptake and catabolism of T4Lhyp released during the natural degradation of collagen contributes to the global recycling of carbon and nitrogen. -Per the rebuttal to R3, the authors have now just deleted the data on W33A (rather than tone down conclusions). This was already in the SI, and not something that was ever a big part of the paper, so this seems fine.

Brown algal cell walls are complex matrices composed primarily of alginate, cellulose, and fucoidan. Their depolymerization is important in marine carbon cycling. Although numerous algal polysaccharide-degrading enzymes have been characterized, most studies focus on breaking down single, purified polysaccharides, leaving the degradation mechanisms of native cell walls containing mixed polysaccharides poorly understood. Here, we report the integrated modular enzymes involved in brown algal cell wall polysaccharide (BACWP) degradation. Using the marine flavobacterium Aquimarina sp. 2-A2 as a model, we isolated a bifunctional enzyme, CelAly, which integrates a glycoside hydrolase family 5 cellulase domain and a polysaccharide lyase family 31 alginate lyase domain within a single polypeptide, enabling the degradation of cellulose and alginate in brown algal cell walls. In vivo relevance of CelAly was confirmed by upregulation of its gene during growth on algal biomass. CelAly also contains three distinctive substrate-binding modules (B1, B2, UKD) that support its multimodular functionality; among these, UKD is notable for its dual substrate-binding capability. CelAly's modular architecture and interdomain flexibility may facilitate coordinated degradation of BACWPs. Bioinformatic analyses and biochemical validation revealed three additional types of such modular enzymes from marine microbes. CelAly and related modular enzymes are strongly associated with marine environments and exhibit conserved modular strategy for substrate recognition and catabolism. Thus, these enzyme architectures represent a previously unrecognized strategy specialized for BACWP decomposition. This study elucidates the unique structural and functional adaptations of the integrated multimodular enzymes and highlights their ecological prevalence among marine bacteria, providing insights into natural biomass decomposition.

Polycyclic aromatic hydrocarbons (PAHs) constitute a significant class of environmental hazards in the atmosphere, posing considerable risks to human health owing to their mutagenic, carcinogenic, and persistent nature. Although some studies have focused on PAHs in human-impacted areas, the characteristics and sources of PAHs in remote regions, such as high-altitude atmospheres, remain to be clarified. During the summer of 2021, we conducted intensive field measurements at the summit of Changbai Mountain (2623 m above sea level), the highest peak in Northeast Asia. Eighteen PAH species were detected in the collected PM2.5 samples, and their chemical compositions, temporal variations, long-range transport, and associated health risks were analyzed. The average PAH concentrations were 0.92 ± 0.36 ng/m³, dominated by compounds containing 2-3 and 5-7 aromatic rings. Backward trajectory analysis underscored the influence of long-range transport on PAH levels at Changbai Mountain, with the air masses originating from the Korean Peninsula characterized by high PAH concentrations. Major sources of PAHs included biomass and coal combustion, vehicle emissions, and oil/gas/petroleum and diagenetic processes. The estimated health risks were below the threshold set by the World Health Organization, indicating minimal carcinogenic risk from atmospheric PAHs at Changbai Mountain. Although this study was conducted only during the summer season, it establishes critical baseline data on transboundary PAH transport patterns in Northeast Asia. These findings provide valuable insights into the long-range transport, sources, and potential health risks of environmental hazards in Northeast Asian regional background atmosphere, and highlighting the necessity for future investigations encompassing seasonal cycle dynamics.

Antarctic krill (Euphausia superba) is a nutrient-rich marine resource. Although several terrestrial proteases have been used to prepare Antarctic krill peptides (AKPs), there has been no report on the preparation of AKPs using a marine protease. Here, marine bacterial protease A69 was used to prepare AKPs with multi-bioactivities. Through optimizing hydrolysis parameters, we established a process for AKPs preparation by hydrolyzing Antarctic krill powder with A69. In the prepared AKPs, peptides less than 3000 Da and 1000 Da accounted for 99.23% and 88.37%, respectively. The scavenging ratios of the AKPs to ABTS+, DPPH· and ·OH reached 93.23 ± 0.09%, 99.90 ± 0.15%, and 93.90 ± 0.47%, respectively. The AKPs also had high angiotensin-converting enzyme (ACE)-inhibitory activity, with an IC50 of 0.22 ± 0.04 mg/mL. At 40 mg/mL, the AKPs inhibited α-glucosidase and dipeptidyl peptidase IV (DPP-IV) activities by 7.18% and 13.62%, respectively, and displayed antibacterial activity to Escherichia coli. Moreover, 14 antioxidant peptides, 24 ACE-inhibitory peptides, 2 α-glucosidase-inhibitory peptides, and 10 DPP-Ⅳ-inhibitory peptides were identified from the AKPs. These results demonstrate that the prepared AKPs contain diverse bioactive peptides and have multi-bioactivities. This study indicates that marine bacterial protease A69 has promising application potential in preparing AKPs with multi-bioactivities.

Phytic acid, also known as inositol hexaphosphate (IP6), is one of the most abundant organophosphorus compounds in nature. Its degradation by phytase plays a key role in the natural phosphorus cycle. In addition, phytases are widely used in livestock and poultry feed to enhance phosphorus utilization. While most reported and commercial phytases are derived from terrestrial organisms, relatively few originate from marine microorganisms, and information on the diversity of phytase-producing marine bacteria remains limited. In this study, following enrichment with sodium phytate, we analyzed the bacterial diversity in seawater and sediment samples collected from the coast of Aoshan Bay in Qingdao, China, using 16S rRNA gene amplicon sequencing. A total of 138 OTUs representing 10 phyla, 15 classes, 37 orders, 55 families, and 70 genera were identified. Furthermore, 27 phytase-producing bacterial strains were isolated from the enrichment cultures, primarily belonging to the phyla Firmicutes (14/27) and Proteobacteria (12/27). Five extracellular phytase genes were identified through genome sequencing of three representative strains. These phytases were subsequently expressed and characterized. All were classified as histidine acid phosphatase-type phytases, exhibiting optimal activity at temperatures of 50–60 °C and pH values of 4.0–5.0. Notably, phytase 3919 showed a specific activity as high as 2485.25 U/mg, indicating strong potential for practical applications. This study provides insight into the diversity of coastal bacteria involved in phytic acid degradation, contributing to our understanding of bacterial-driven phosphorus cycling in coastal ecosystems and facilitating the discovery of phytases with industrial potential.

The use of natural biomaterials in flame retardant formulations as sustainable alternatives has gained significant interest in recent years. Given the high-risk environment in which airplanes operate, aviation safety remains a top priority. Flame retardants (FRs) are crucial for preventing or reducing the spread of flames in flammable materials used in aircraft construction and interior furnishings, thus mitigating fire risks. This study aims to analyze the molecular-level influence of natural biomaterials on aviation flame retardant performance, with a focus on lignin. Lignin, a natural polymer derived from plant cell walls, offers an environmentally friendly alternative to conventional synthetic flame retardants. Lignin-based composites can be applied to various aircraft components, such as wings and fuselage. The study employs Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Nuclear Magnetic Resonance (NMR) to investigate the molecular interactions of these biomaterials. Additionally, to assess thermal stability and degradation, Thermo-gravimetric Analysis (TGA) is utilized. The results indicate that lignin enhances flame retardancy by promoting the formation of a protective char layer and improving thermal stability. This research also provides insights into the molecular mechanisms underlying lignin’s effectiveness as a flame retardant and explores its potential in developing high-performance aircraft flame retardants.

Marine bacterial proteases have rarely been used to produce bioactive peptides, although many have been reported. This study aims to evaluate the potential of the marine bacterial metalloprotease A69 from recombinant Bacillus subtilis in the preparation of peanut peptides (PPs) with antioxidant activity and angiotensin-converting enzyme (ACE)-inhibitory activity. Based on the optimization of the hydrolysis parameters of protease A69, a process for PPs preparation was set up in which the peanut protein was hydrolyzed by A69 at 3000 U g−1 and 60 °C, pH 7.0 for 4 h. The prepared PPs exhibited a high content of peptides with molecular weights lower than 1000 Da (>80%) and 3000 Da (>95%) and contained 17 kinds of amino acids. Moreover, the PPs displayed elevated scavenging of hydroxyl radical and 1,1-diphenyl-2-picryl-hydrazyl radical, with IC50 values of 1.50 mg mL−1 and 1.66 mg mL−1, respectively, indicating the good antioxidant activity of the PPs. The PPs also showed remarkable ACE-inhibitory activity, with an IC50 value of 0.71 mg mL−1. By liquid chromatography mass spectrometry analysis, the sequences of 19 ACE inhibitory peptides and 15 antioxidant peptides were identified from the PPs. These results indicate that the prepared PPs have a good nutritional value, as well as good antioxidant and antihypertensive effects, and that the marine bacterial metalloprotease A69 has promising potential in relation to the preparation of bioactive peptides from peanut protein.

Alginate, mainly produced by brown algae, is an important polysaccharide that supports the growth of marine bacteria. Vreelandella sp. F11 is a Gram-negative and aerobic marine bacterium, which was isolated from the brown algae sample collected from the Weihai coast, the Yellow Sea, China. Here, we present the complete genome of strain F11 and its genomic characteristics to utilize alginate. The genome of strain F11 comprises one circular chromosome with 4,840,724 bp and a GC content of 55.04 %. Strain F11 could grow with alginate as the sole carbon source. Genomic analysis revealed that strain F11 contains a gene cluster, encoding the enzymes, transporters and a regulator protein involved in utilizing alginate. Gene annotations suggested that the alginate utilization system of strain F11 is similar to those in Vibrio strains. However, strain F11 does not contain homologs of known KdgF (a key enzyme involved in the metabolism of alginate monomer) and inner membrane transporters of alginate oligomer uptake. The result indicated that strain F11 contains novel KdgF and inner membrane transporter system, which warrants further investigation. These data suggested that Vreelandella strains play a role in alginate utilization in the ocean and lay a foundation for the application of Vreelandella in the conversion of brown algae.

Nitrogen dioxide (NO2) poses a critical potential risk to environmental quality and public health. A reliable machine learning (ML) forecasting framework will be useful to provide valuable information to support government decision-making. Based on the data from 1609 air quality monitors across China from 2014-2020, this study designed an ensemble ML model by integrating multiple types of spatial-temporal variables and three sub-models for time-sensitive prediction over a wide range. The ensemble ML model incorporates a residual connection to the gated recurrent unit (GRU) network and adopts the advantage of Transformer, extreme gradient boosting (XGBoost) and GRU with residual connection network, resulting in a 4.1%±1.0% lower root mean square error over XGBoost for the test results. The ensemble model shows great prediction performance, with coefficient of determination of 0.91, 0.86, and 0.77 for 1-hr, 3-hr, and 24-hr averages for the test results, respectively. In particular, this model has achieved excellent performance with low spatial uncertainty in Central, East, and North China, the major site-dense zones. Through the interpretability analysis based on the Shapley value for different temporal resolutions, we found that the contribution of atmospheric chemical processes is more important for hourly predictions compared with the daily scale predictions, while the impact of meteorological conditions would be ever-prominent for the latter. Compared with existing models for different spatiotemporal scales, the present model can be implemented at any air quality monitoring station across China to facilitate achieving rapid and dependable forecast of NO2, which will help developing effective control policies.

The deep marine sediments represent a major repository of organic matter whilst hosting a great number of uncultivated microbes. Microbial metabolism plays a key role in the recycling of organic matter in the deep marine sediments. D-amino acids (DAAs) and DAA-containing muropeptides, an important group of organic matter in the deep marine sediments, are primarily derived from bacterial peptidoglycan decomposition. Archaea are abundant in the deep ocean microbiome, yet their role in DAA metabolism remains poorly studied. Here, we report bioinformatic investigation and enzymatic characterization of deep marine sedimentary archaea involved in DAA metabolism. Our analyses suggest that a variety of archaea, particularly the Candidatus Bathyarchaeota and the Candidatus Lokiarchaeaota, can metabolize DAAs. DAAs are converted into L-amino acids via amino acid racemases (Ala racemase, Asp racemase and broad substrate specificity amino acid racemase), and converted into α-keto acid via d-serine ammonia-lyase, whereas DAA-containing di-/tri-muropeptides can be hydrolyzed by peptidases (dipeptidase and D-aminopeptidase). Overall, this study reveals the identity and activity of deep marine sedimentary archaea involved in DAA metabolism, shedding light on the mineralization and biogeochemical cycling of DAAs in the deep marine sediments.

Alginate oligosaccharides (AOs), derived from alginate degradation, exhibit diverse biological activities and hold significant promise in various fields. The enzymatic preparation of AOs relies on alginate lyases, which offers distinct advantages. In contrast to the conventional use of sodium alginate derived from brown algae as the substrate for the enzymatic preparation of AOs, AO preparation directly from brown algae is more appealing due to its time and energy efficiency. Thus, the identification of potent alginate lyases and cost-effective brown algae substrates is crucial for optimizing AO production. Herein, we identified and characterized an alginate lyase, AlyP18, capable of efficiently decomposing algae, from a marine bacterium Pseudoalteromonas agarivorans A3 based on secretome analysis. AlyP18 is a mesothermal, endo-type and bifunctional alginate lyase with high enzymatic activity. Two brown algae substrates, Laminaria japonica roots and Macrocystis pyrifera, were used for the AO preparation by AlyP18. Upon optimization of AlyP18 hydrolysis parameters, the substrate degradation efficiency and AO production reached 53% and ~32% for L. japonica roots, respectively, and 77% and ~46.5% for M. pyrifera. The generated AOs primarily consisted of dimers to pentamers, with trimers and tetramers being dominant. This study provides an efficient alginate lyase and alternative brown algal feedstock for the bioconversion of high-value AOs from brown algae.

Alginate oligosaccharides (AOS), products of alginate degradation by endotype alginate lyases, possess favorable biological activities and have broad applications. Although many have been reported, alginate lyases with homogeneous AOS products and secretory production by an engineered host are scarce. Herein, the alginate lyase AlyC7 from Vibrio sp. C42 was characterized as a trisaccharide-producing lyase exhibiting high activity and broad substrate specificity. With PelB as the signal peptide and 500 mM glycine as the additive, the extracellular production of AlyC7 in Escherichia coli reached 1122.8 U/mL after 27 h cultivation in Luria-Bertani medium. The yield of trisaccharides from sodium alginate degradation by the produced AlyC7 reached 758.6 mg/g, with a purity of 85.1%. The prepared AOS at 20 μg/mL increased the root length of lettuce, tomato, wheat, and maize by 27.5%, 25.7%, 9.7%, and 11.1%, respectively. This study establishes a robust foundation for the industrial and agricultural applications of AlyC7.

ABSTRACT Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae ( Xoo ) is one of the most destructive diseases in rice. However, the pathogenic mechanisms of Xoo have not been fully understood. In this study, we identified a novel ferric uptake regulator (Fur) protein, XanFur, in Xoo, which is conserved among the major pathogens of Xanthomonas species, but has no obvious sequence identity with reported Fur proteins. Gene deletion indicated that xanfur is required for the full virulence of Xoo in rice. The expression of xanfur was significantly induced by 0.1 mM H 2 O 2 and its deletion caused a significant decrease in the tolerance of Xoo to H 2 O 2 , suggesting that xanfur is likely involved in the resistance of Xoo to the oxidative stress caused by H 2 O 2 in rice. The loss of xanfur also caused significant reduction in extracellular polysaccharide production, biofilm formation, and cell motility, suggesting that xanfur may be also involved in regulating these virulence determinants of Xoo . Furthermore, both in vivo and in vitro experimental results demonstrated that the global transcriptional regulator Clp positively regulated the expression of xanfur by directly binding to its promoter region, especially in the presence of 0.1 mM H 2 O 2 , presenting the cellular regulatory pathway for the expression of this gene. These results not only contribute to a better understanding of the interaction mechanisms between rice and Xoo , but also provide reference to developing high-effective bactericides by targeting to the Fur protein in Xoo to control bacterial leaf blight in rice. IMPORTANCE Although Xanthomonas oryzae pv. oryzae ( Xoo ) has been found to be a bacterial pathogen causing bacterial leaf blight in rice for many years, the molecular mechanisms of the rice- Xoo interaction has not been fully understood. In this study, we found that XanFur of Xoo is a novel ferric uptake regulator (Fur) protein conserved among major pathogenic Xanthomonas species. XanFur is required for the virulence of Xoo in rice, and likely involved in regulating the virulence determinants of Xoo . The expression of xanfur is induced by H 2 O 2 , and positively regulated by the global transcriptional regulator Clp. Our results reveal the function and regulation of the novel virulence-related Fur protein XanFur in Xoo, providing new insights into the interaction mechanisms of rice- Xoo .

Abstract. Narrowing surface ozone disparities between urban and nonurban areas escalate health risks in densely populated urban zones. A comprehensive understanding of the impact of ozone photochemistry processes on this transition remains constrained by our knowledge of aerosol effects and the spatial availability of surface monitoring. Here we developed a novel deep learning framework, which could perceive spatiotemporal dynamics from adjacent grids by multidimensional self-attention operation, integrating multi-sources data to estimate daily 500 m surface ozone, nitrogen dioxide (NO2) and fine particulate matter (PM2.5) concentrations. Subsequently, three distinct ozone formation regimes linked with its precursors, aerosols, and meteorology were delineated through an interpretable machine learning method. The evaluations of the framework exhibited average out-of-sample cross-validation coefficient of determination of 0.96, 0.92 and 0.95 for ozone, NO2 and PM2.5, respectively. In 2020, urban ozone levels in Shandong surpassed those in nonurban due to a more pronounced decrease in ozone in the latter where PM2.5 is the dominant anthropogenic driver. The ozone sensitivity to volatile organic compounds (VOCs), the dominant regime in urban areas, was observed to shift towards a NOx-limited when extended to rural areas. A third ‘aerosol-inhibited’ regime was identified in the Jiaodong Peninsula, where the uptake of hydroperoxyl radicals onto aerosols suppressed ozone production under low NOx levels during summertime. The reduction of PM2.5 would increase the sensitivity of ozone to VOCs, necessitating more stringent VOC emission abatement for urban ozone mitigation. Our case study demonstrates the critical need for advanced modeling approaches providing finer spatially resolved estimations.