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Organic fertilizers increase soil organic matter (SOM) stocks, but the underlying processes depend on the fertilizer type and remain largely unknown. To evaluate the predominant C stabilization mechanisms, upland Ultisols subjected to 27 years of mineral and organic fertilization were analyzed for SOM content, aggregate size classes, and amino sugar composition. The long-term field experiment had seven treatments: no fertilization (Control), mineral NPK fertilizers (NPK), NPK plus lime (NPK + Lime), NPK plus peanut straw (NPK + PeanutStraw), NPK plus rice straw (NPK + RiceStraw), NPK plus radish residue (NPK + RadishResidue), and NPK plus pig manure (NPK + PigManure). The 27-year application of mineral fertilizers (NPK and NPK + Lime), NPK + crop residues, and NPK + PigManure increased SOM content by 11.0–13.2%, 16.3–25.3%, and 44.3%, respectively, compared with the Control. The aliphaticity and recalcitrance indices based on 13C nuclear magnetic resonance spectra of organic fertilizers were higher for pig manure than for crop residues. Both indices were closely correlated with SOM content after 27 years, so higher proportions of recalcitrant C in manure facilitated SOM accumulation. NPK + PigManure increased the mass proportion of large macroaggregates 2.9-fold compared with the Control, and reduced the effective diffusion coefficient of oxygen in the soil. Consequently, NPK + PigManure limited the activity and abundance of aerobes and the accessibility of SOM to microorganisms, in turn facilitating SOM accumulation. The application of mineral fertilizers, NPK + crop residues, and NPK + PigManure increased microbial necromass to 2.85–3.03, 3.21–3.45, and 3.62 g C kg−1, respectively, from 2.63 g C kg−1 in the Control. Compared with crop residues, pig manure did not affect bacterial necromass but increased fungal necromass from 2.19 to 2.39 g C kg−1 to 2.58 g C kg−1, which might associate with increased SOM stability. However, the relative contribution of microbial necromass to SOM was lower under NPK + PigManure than under NPK + crop residues, since more added C was protected in the NPK + PigManure soil. Our results suggest that manure may contribute to SOM accumulation and stabilization in three ways: directly through the input of recalcitrant organic C, indirectly through the stabilization of aggregates and physical protection of C, and to a lesser extent through increasing fungal necromass.

An efficient synthesis of biologically important benzylidene-indolin-2-one derivatives using meglumine as green catalyst and ethanol:water as reaction media at 78°C has been developed. The effects of reaction conditions such as solvents, temperature, and amount of catalyst were investigated. The present methodology offers many advantages such as simple procedure, less time taking to complete the reaction, high yield of products, and clean reaction profile.

Subtropical ecosystems are generally characterized by phosphorus (P)-deficient soils; however, extreme P-rich soils develop on phosphate rocks. We aimed to integrate metabolomic and ionomic analyses to survey how in situ trees adaptively respond to such contrasting P soils. Gas (GC-MS) or liquid (LC-MS) chromatography-mass spectrometry and inductively coupled plasma-optical emission spectrometer (ICP-OES) were used to analyze leaf metabolome and ionome of Quercus variabilis, which grew at two geologic P-rich and P-deficient sites in subtropical China. Two Q. variabilis populations were significantly discriminated in terms of metabolome and ionome, with major contributions from 25 identified metabolites (e.g. sugars and P-containing compounds) and P and four other chemical elements. And of these 25 metabolites, orthophosphate was predominant in influencing the variation in the metabolomes of Q. variabilis between the two P-type sites. Moreover, orthophosphate was correlated with leaf P (r = 0.85, p

O-polysaccharide (O-antigen) was isolated from the lipopolysaccharide of Vibrio cholerae O100 and studied by component analyses and 1D and 2D NMR spectroscopy. The following structure of the O-polysaccharide was established: →3)-β- d -QuipNAc4N(dHh)-(1 → 3)-α- d -Fucp4N(RHb)-(1 → 3)-α- l -FucpNAc-(1→ where Hb and dHh indicate 3-hydroxybutanoyl and 3,5-dihydroxyhexanoyl, respectively. The O-antigen gene cluster of V. cholerae O100 has been sequenced. The gene functions were tentatively assigned by comparison with sequences in the available databases and found to be in agreement with the OPS structure.

Almond consumption can improve cardiometabolic (CM) health. However, the mechanisms underlying those benefits are not well characterized. This study explored the effects of consuming a snack of almonds vs. crackers for 8 weeks on changes in metabolomic profiles in young adults (clinicaltrials.gov ID: NCT03084003). Participants (n=73, age: 18-19 years, BMI: 18-41 kg/m2) were randomly assigned to consume either almonds (2 oz/d, n=38) or an isocaloric control snack of graham crackers (325 kcal/d, n=35) daily for 8 weeks. Blood samples were collected at baseline prior to and at 4 and 8 weeks after the intervention. Metabolite abundances in the serum were quantified by hydrophilic interaction chromatography quadrupole (Q) time-of-flight (TOF) mass spectrometry (MS/MS), gas chromatography (GC) TOF MS, CSH-ESI (electrospray) QTOF MS/MS, and targeted analyses for free PUFAs, total fatty acids, oxylipins and endocannabinoids. Linear mixed model analyses with baseline-adjustment were conducted, and those results were used for enrichment and network analyses. Microbial community pathway predictions from 16S rRNA sequencing of fecal samples was done using PICRUST2. Almond consumption enriched unsaturated triglycerides, unsaturated phosphatidylcholines, saturated and unsaturated lysophosphatidylcholines, tricarboxylic acids, and tocopherol clusters (p

The development of a flexible, component-based synthetic route to the aminosugar fragment of the lincosamide antibiotics is described. This synthetic route hinges on the application and extension of nitroaldol chemistry to forge strategic bonds within complex aminosugar targets, and employs a glycal epoxide as a versatile glycosyl donor for the installation of various anomeric groups. Through building-block exchange and late-stage functionalization, this route affords access to a host of rationally designed lincosamides otherwise inaccessible by semisynthesis, and underpins a platform for the discovery of new lincosamide antibiotics.

The objective of this experiment was to study the effect of cotton residues incorporation on soil properties, soil organic nitrogen (N) fractions, and N-mineralizing enzyme (protease, and urease) activity in the 0–40 cm soil layer in the long-term continuous cotton field. In this experiment, seven treatments, including cotton residues incorporation for 5, 10, 15 and 20 years (marked as 5a, 10a, 15a, and 20a) and continuous cropping for 5, 10 and 20 years (marked as CK5, CK10 and CK20) were conducted. The results showed that the soil organic carbon (C) and N increased gradually with the increase in the duration of continuous cropping with cotton residues incorporation. Compared with CK20, the 20a treatments reduced the content of amino acid N (AAN), ammonium N (AN), amino sugar N (ASN), hydrolysable unidentified N (HUN), and acid insoluble N (AIN) significantly by 48.6, 32.2, 96.9, 48.3, and 38.7%, respectively (p p

N-sugar substituted chiral aziridines were synthesized via Gabriel-Cromwell reaction. Novel pure diastereomers of aziridine derivatives (4 diastereomers) were readily obtained in high yields and their structures were confirmed by means of 1H NMR, 13C NMR, FT-IR, Mass and optical rotations. This is, to the best of our knowledge, the unique example of N-sugar aziridine synthesis. Diastereomeric effects for prostate (PC3) and cervix (HeLa) cancers were screened and it has been observed that the epimers bearing the same sugars showed different results against PC3 and HeLa cancer cells. The novel sugar aziridines were investigated as promising prodrug candidates for prostate cancer (PC3) therapy. Moreover, the drug likeness calculations (Lipinski's rule, physicochemical properties, lipophilicity, solubility, pharmacokinetics and bioavailability radar) have indicated that the sugar aziridines can be good candidates as oral drugs.

Pearl oyster Pinctada fucata martensii is widely recognized for biomineralization and has been cultured for high-quality marine pearl production. To ascertain how dietary vitamin D3 (VD3) levels affect the features of pearl production by P. f. martensii and discover the mechanisms regulating this occurrence, five experimental diets with variable levels of VD3 were used with inclusion levels of 0, 500, 1,000, 3,000, and 10,000 IU/kg. The distinct inclusion levels were distributed into five experimental groups (EG1, EG2, EG3, EG4, and EG5). All the experimental groups were reared indoors except the control group (CG) reared at the sea. Pearl oysters, one year and a half old, were used in the grafting operation to culture pearls. During the growing period that lasted 137 days, EG3 had the highest survival rate, retention rate, and high-quality pearl rate. A similar trend was found for EG3 and CG with significantly higher pearl thickness and nacre deposition rates than other groups, but no significant differences were observed between them. A metabolomics profiling using GC–MS and LC–MS of pearl oysters fed with low quantities of dietary VD3 and optimal levels of dietary VD3 revealed 135 statistically differential metabolites (SDMs) (VIP > 1 and p < 0.05). Pathway analysis indicated that SDMs were involved in 32 pathways, such as phenylalanine metabolism, histidine metabolism, glycerophospholipid metabolism, alanine aspartate and glutamate metabolism, arginine and proline metabolism, glycerolipid metabolism, amino sugar and nucleotide sugar metabolism, and tyrosine metabolism. These results provide a theoretical foundation for understanding the impacts of VD3 on pearl production traits in pearl oyster and reinforce forthcoming prospects and application of VD3 in pearl oyster in aquaculture rearing conditions.

Global warming may have a great impact on soil organic carbon (SOC) turnover in permafrost peatlands. The response of microbial residues, as precursors of SOC, to climate warming remains unknown. A 6-year in situ warming experiment was conducted in the permafrost peatlands of Great Hing'an Mountains. Three commonly used amino sugars (glucosamine, GluN; galactosamine, GalN; muramic acid, MurA), for the quantification of microbial residues, were determined in two depths (0–15 cm, shallow soil; 15–30 cm, deep soil) of the bulk and rhizosphere soil of the shrub and Eriophorum vaginatum L. The amount of GluN, GalN, and MurA in deep shrub rhizosphere soil in the warming treatment decreased by 12.65%, 26.11%, and 14.78%, respectively, as compared to that in the control treatment. Yet, warming did not alter the amount of amino sugars in shallow and deep bulk soil. Warming decreased the concentrations of GluN, MurA, and total amino sugars in the deep rhizosphere soil of Eriophorum vaginatum L. by 22.04%, 26.14%, and 18.71%, respectively. Amino sugars in the deep rhizosphere soil of Eriophorum vaginatum L. had a higher temperature sensitivity than those in the deep bulk soil, while total amino sugars in the shallow rhizosphere soil of Eriophorum vaginatum L. had a lower temperature sensitivity than those in the deep rhizosphere soil.

The industrial and agricultural applications of rare earth elements (REEs) lead to considerable REE emissions into environment. Yet, little is known about the molecular-level effects and interactions of REEs in terrestrial plants. Herein, the individual and joint effects of La and Ce in Triticum aestivum were investigated using mass spectrometry-based metabolomics. Metabolic effect level index (MELI) was utilized as a readable endpoint for quantifying mixture interactions. Exposure to single La/Ce at environmentally relevant levels induced significant dose-dependent metabolic changes. The highly overlap of differential metabolites and perturbed pathways of La and Ce suggested their similar mode of action. Exposure to La-Ce mixtures did not induce additional metabolic pathway perturbation. Specifically, metabolism of amino sugar and nucleotide sugar, starch and sucrose, fructose and mannose, glycerophospholipid and purine were disrupted for both single and binary exposures. These results, together with physiological indicators, point to REE-induced oxidative stress, energy expenditure, DNA damage and membrane disturbance. The MELI calculations showed that La and Ce interacted synergistically at the overall metabolic level, which could be causally linked to synergistic interaction at the individual level (root elongation). This work proved metabolomics could be an important and effective strategy for interpreting toxicity and interactions of REE mixtures.

Although solid-phase activation of lignite using a nanocatalyst has great potential in producing low-cost and sustainable humic acid, the large-scale application of this technology still faces challenges because of the high price and toxicity of the nanocatalyst. Additionally, the specific molecular components of humic acid in activated lignite remain unknown. In this work, a multifunctional molybdate-phosphorus hierarchical hollow nanosphere (Mo-P-HH) catalyst was successfully manufactured by a simple way followed by phosphorization. In comparison with a commercial Pd/C catalyst, the multifunctional Mo-P-HH catalyst was more effective in producing water-soluble humic acid with small molecular functional groups from lignite via solid-phase activation. Moreover, Fourier transform ion cyclotron resonance mass spectrometry revealed the molecular compositions of humic acid in activated lignite. Compared with that from raw lignite, the humic acid after Mo-P-HH activation had less aromatic structure but higher content of lipids, proteins, amino sugar, and carbohydrates. In addition, the activated humic acid simulated seed germination and seedling growth. Therefore, this study provided a high-performance hierarchical hollow nanocatalyst for activation of humic acid and also offered the theoretical basis for the application of humic acid in agriculture.

Department of Chemistry, West Bengal State University, Barasat, Kolkata-700 126, India E-mail: jhimli.sengupta@gmail.com Manuscript received online 12 October 2020, revised and accepted 30 November 2020 Carbohydrate-based organic Schiff bases having biological, catalytic and pharmaceutical activities have great demand. A se­ries of new organic Schiff bases were synthesized starting from diacetone-D-glucose following the general protocol of con­densation between amine and aldehyde, either both having sugar moiety (condensation of amino sugar with aldehyde sugar), and/or at least one component having sugar moiety. All the compounds that we synthesised were characterised by NMR, FT­IR, and mass spectral studies. One of the organic Schiff base SSB-4 which was synthesized by condensation of amino sugar with aldehyde sugar, expected to be a good precursor for the synthesis of macrocycle and might also show some biological activity.

Despite the importance of subsoil carbon (C) deposition by deep-rooted crops in mitigating climate change and maintaining soil health, the quantification of root C input and its microbial utilization and stabilization below 1 m depth remains unexplored. We studied C input by three perennial deep-rooted plants (lucerne, kernza, and rosinweed) grown in a unique 4-m deep RootTower facility. 13C multiple pulse labeling was applied to trace C flows in roots, rhizodeposition, and soil as well as 13C incorporation into microbial groups by phospholipid fatty acids and the long-term stabilization of microbial residues by amino sugars. The ratio of rhizodeposited 13C in the PLFA and amino sugar pools was used to compare the relative microbial stability of rhizodeposited C across depths and plant species. Belowground C allocation between roots, rhizodeposits, and living and dead microorganisms indicated depth dependent plant investment. Rhizodeposition as a fraction of the total belowground C input declined from the topsoil (0–25 cm) to the deepest layer (360 cm), i.e., from 35%, 45%, and 36%–8.0%, 2.5%, and 2.7% for lucerne, kernza, and rosinweed, respectively, where lucerne had greater C input than the other species between 340 and 360 cm. The relative microbial stabilization of rhizodeposits in the subsoil across all species showed a dominance of recently assimilated C in microbial necromass, thus indicating a higher microbial stabilization of rhizodeposited C with depth. In conclusion, we traced photosynthates down to 3.6 m soil depth and showed that even relatively small C amounts allocated to deep soil layers will become microbially stabilized. Thus, deep-rooted crops, in particular lucerne are important for stabilization and storage of C over long time scales in deep soil.

Atmospheric nitrogen (N) deposition has a significant influence on soil organic carbon (SOC) accumulation in forest ecosystems. Microbial residues, as by-products of microbial anabolism, account for a significant fraction of soil C pools. However, how N deposition affects the accumulation of soil microbial residues in different forest biomes remains unclear. Here, we investigated the effects of six/seven-year N additions on microbial residues (amino sugar biomarkers) in eight forests from tropical to boreal zone in eastern China. Our results showed a minor change in the soil microbial residue concentrations but a significant change in the contribution of microbial residue-C to SOC after N addition. The contribution of fungal residue-C to SOC decreased under low N addition (50 kg N ha−1 yr−1) in the tropical secondary forest (−19%), but increased under high N addition (100 kg N ha−1 yr−1) in the temperate Korean pine mixed forest (+21%). The contribution of bacterial residue-C to SOC increased under the high N addition in the subtropical Castanopsis carlesii forest (+26%) and under the low N addition in the temperate birch forest (+38%), respectively. The responses of microbial residue-C in SOC to N addition depended on the changes in soil total N concentration and fungi to bacteria ratio under N addition and climate. Taken together, these findings provide the experimental evidence that N addition diversely regulates the formation and composition of microbial-derived C in SOC in forest ecosystems.

N-acetylglucosamine 6-phosphate deacetylase (NagA) catalyzes the conversion of N-acetylglucosamine-6-phosphate to glucosamine-6-phosphate in amino sugar catabolism. This conversion is an essential step in the catabolism of sialic acid in several pathogenic bacteria, including Pasteurella multocida, and thus NagA is identified as a potential drug target. Here, we report the unique structural features of NagA from P. multocida (PmNagA) resolved to 1.95 A. PmNagA displays an altered quaternary architecture with unique interface interactions compared to its close homolog, the Escherichia coli NagA (EcNagA). We confirmed that the altered quaternary structure is not a crystallographic artifact using single particle electron cryo-microscopy. Analysis of the determined crystal structure reveals a set of hot-spot residues involved in novel interactions at the dimer-dimer interface. PmNagA binds to one Zn2+ ion in the active site and demonstrates kinetic parameters comparable to other bacterial homologs. Kinetic studies reveal that at high substrate concentrations (~10-fold the KM ), the tetrameric PmNagA displays hysteresis similar to its distant neighbor, the dimeric Staphylococcus aureus NagA (SaNagA). Our findings provide key information on structural and functional properties of NagA in P. multocida that could be utilized to design novel antibacterials.

Soil microbial necromass represents a significant proportion (>50%) of soil organic matter (SOM). Microbial necromass consists mainly of particulate organic residues from fragmented cells walls and other slow turnover cytoplasmic components of dead fungi and bacteria. Some of the key components of microbial cell walls, such as peptides and amino sugar polymers, can remain and accumulate in the soil over prolonged times. Amino sugars have been used as biomarkers to quantify the contribution of microbial necromass to stabilized SOM. The different amino sugars present in polymeric form in soils can be released by acid hydrolysis and allow the estimation of the contribution of both fungal and bacterial necromass to the SOM pool. Among the amino sugars, hexosamine isomers (glucosamine, galactosamine, mannosamine) and muramic acid (the ether of lactic acid and glucosamine) are the most abundant ones. Muramic acid is specific to bacterial peptidoglycan while glucosamine is an abundant cell wall component of both, fungal chitin and bacterial peptidoglycan.There are several chromatographic methods to measure free and bound amino sugars and amino acids in soil extracts and soil hydrolysates, but none of them allow the combined determination of amino sugar biomarkers and amino acids simultaneously in a single assay for rapid analysis. This is important as a large fraction of soil necromass N (>50%) consists of non-amino sugar-N, such as proteins and nucleic acids. In this study we therefore adopt a method based on 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AccQ.Tag) derivatization of amino compounds and optimized chromatographic (reversed phase) separation to simultaneously measure amino sugars (isomers) and amino acids in soil extracts and soil hydrolysates using ultra-high-performance liquid chromatography coupled to fluorescence or UV detection.The use of this method allows for fast, robust and highly sensitive quantification of amino acids and amino sugars in environmental samples at sub-micromolar levels. This approach will help to improve our understanding of soil microbial necromass dynamics and their inherent effect on soil C and N sequestration. The AccQ.Tag chemistry also allows compound detection by electrospray ionization (ESI)-mass spectrometry, enabling isotope (13C, 15N) tracing applications.

The cation-independent bioflocculant (59LF) extracted from Klebsiella sp. 59L was characterized. 59LF consisted of protein (4.8%) and total sugar (85.2%) with high molecular weight (93.82% of 2120 kDa), and total sugar was composed of 76.45% of neutral sugar, 3.65% of uronic acid, and 1.43% of amino sugar. Results indicated that 59LF was pH tolerant and thermally stable, and the maximum yield of 59LF was 4.078 g/L after 48 h culture. The optimal flocculating activity for Kaolin particles was obtained when the dosage of 59LF was 7.0 mg/L without additional metal ions as coagulant aids. Furthermore, the surface properties of 59LF were observed using a Fourier-transform infrared spectrophotometer and X-ray photoelectron spectroscopy, whereas a porous structure was detected by a scanning electron microscope. Thus, a primary flocculation mechanism of 59LF was proposed. This study provided a potential cation-independent bioflocculant with high productivity and low dosage in future application.

Amino acids (AA) and, more recently, amino sugars (AS) in marine or lacustrine sediments have been increasingly used as paleoproxies. In order to assess AA and AS compositional changes during simulated microbial degradation, as well as to understand the importance of amino-compound re-synthesis by microbes during early diagenesis, decomposition experiments (300 days) were performed with algal (Fragilaria crotonensis) organic matter (OM)/quartz-sand mixtures under controlled redox conditions. Despite expected greater overall degradability under oxic conditions, decomposition kinetics of the bulk algal OM, as well as the total particulate AA and AS were similar under oxic and anoxic conditions, following exponential decay kinetics consistent with the observed mobilization and transfer of large parts of the particulate organic carbon (C) and nitrogen (N) into the dissolved inorganic and organic C and N pools. Carbon-normalized AA and AS yields suggest relative enrichment of amino compounds during partial decomposition, indicating the production and accumulation of microbial biomass during early diagenesis, independent of the redox environment. Moreover, AA and AS compositional changes, such as the relative enrichment of the AA glycine and the AS muramic acid (MurA), and the decrease in the molar ratio of glucosamine and galactosamine (GlcN:GalN) during degradation in both redox systems, were consistent with significant bacterial re-synthesis and the preferential preservation of bacterial biomaterial with increasing diagenesis. Large disparities between different bacterial amino-sugar based estimates of bacterial contribution indicate that bacterial end-member compositions are not currently known well enough to make these bacterial-biomarker constraints quantitative. However, the overall trends are consistent, indicating substantial turnover of eukaryotic into bacterial OM on short time scales of weeks to months. Together these results suggest that the influence of bacterial reworking in conserving sedimentary OM via its transfer into more refractory OM pools may be substantially greater than previously appreciated. We also investigated established amino-compound based indicators of OM degradation, bacterial synthesis, and sediment reactivity. Despite discrepancies, which we attribute to different susceptibilities of the respective indicators towards degradational changes on different time-scales, the tested indices were overall consistent with past data. These results therefore confirm their value as universal indicators of OM diagenesis. Together, our data highlight the vital role of bacterial reworking on the composition of sedimentary OM, with important implications for the alteration of primary geochemical signatures during early sedimentary diagenesis and their use as proxies in paleoenvironmental studies., Geochimica et Cosmochimica Acta, 283, ISSN:0016-7037, ISSN:1872-9533

Differences in the concentration of metabolites in the biofluids of animals closely reflect their physiological diversities. In order to set the basis for a metabolomic atlas for giant panda (Ailuropoda melanoleuca), we characterized the metabolome of healthy giant panda feces (23), urine (16), serum (6), and saliva (4) samples by means of 1H NMR. A total of 107 metabolites and a core metabolome of 12 metabolites was quantified across the four biological matrices. Through univariate analysis followed by robust principal component analysis, we were able to describe how the molecular profile observed in giant panda urine and feces was affected by gender and age. Among the molecules modified by age in feces, fucose plays a peculiar role because it is related to the digestion of bamboo's hemicellulose, which is considered as the main source of energy for giant panda. A metagenomic investigation directed toward this molecule showed that its concentration was indeed positively related to the two-component system pathway and negatively related to the amino sugar and nucleotide sugar metabolism pathway. Such work is meant to provide a robust framework for further -omics research studies on giant panda to accelerate our understanding of the interaction of giant panda with its natural environment.

Heterotrophic soil microbes are increasingly recognized as a key mediator transforming labile organic carbon (OC) into relatively stable soil carbon (C) in the form of microbial necromass (dead cells) and extracellular compounds associated with minerals. However, the accumulation of microbial necromass relative to labile OC consumption and its regulating factors remain poorly understood, although it has vital implications for soil C sequestration and modeling. Here by mimicking microbial C accumulation in constructed model soils using fructose as the sole OC substrate, we present a benchmark comparison of microbial C accrual versus OC mineralization under declining substrate availability and mineralogy. By quantifying various microbial components including biomass (living cells; indicated by phospholipid fatty acids), necromass (indicated by amino sugars) and total microbial C (including biomass, necromass and extracellular compounds; estimated as the difference between added and residual substrate C minus respiration) in a simple soil system, we compare microbial metabolic quotient (qCO2; i.e., microbial respiration rate per unit of biomass), amino sugar accumulation efficiency (AAE; i.e., ratio of amino sugars to respiration) and microbial C accumulation efficiency (mCAE; i.e., ratio of total microbial C to total microbial C and respiration), and assess their regulating factors. We find that while clay (bentonite) promotes microbial respiration, it enhances the rate as well as efficiency of amino sugar accumulation without affecting qCO2 or mCAE. On the contrary, ferrihydrite increases qCO2 and decreases AAE but promotes labile OC preservation via inhibiting microbial growth in the alkaline model soil. Hence, amino sugar accrual is more efficient in clay-rich model soils while labile OC is less consumed in model soils containing iron (hydr)oxide. Furthermore, while mCAE was correlated with qCO2 in all but the model soil with 6% clay, AAE was correlated with qCO2 only in model soils with 12% clay when the mineral treatments were considered separately. Collectively, our findings suggest that mCAE and AAE heavily depend on mechanisms preserving microbial C components but not solely on the metabolic efficiency and is mediated by soil mineral content as well as composition. Parameters considering microbial C preservation such as mCAE or AAE warrant further study for modelling and managing the formation of microbial derived stable soil OC.

Understanding the response of microbial-derived nitrogen (N) in the soil to N availability is essential for optimizing N fertilizer management. In this study, based on amino sugar biomarker assays in a conservation tillage agroecosystem, we evaluated the effects of 3-year fertilizer N reduction (reduced from 240 to 190, 135, 0 kg N ha−1) and crop residue return on microbial necromass N dynamics. The stock of microbial necromass N declined with the decrease of N input, and the decline of bacterial necromass was greater than that of fungal necromass. However, the decrease of 7.3% in microbial necromass N following the cessation of fertilization indicated a dominant role of microbial necromass in soil N retention despite its compensation ability for N demand. Maize residue return alleviated N deficiency in the soil-crop system and favored the maintenance of the soil organic N pool by preferentially improving the net accumulation of fungal necromass.

Soil organic carbon (SOC) has significant implications in regulating soil health. Emerging insights emphasize the important role of microbial anabolism in SOC storage by continuously transforming plant fragments into persistent microbial residues. However, knowledge of the sequestration pathway of root versus shoot carbon (C) is under debate. While recent studies have shown that labile shoot residue is disproportionately important for stable SOC accumulation through microbial assimilation, how plant root vs. shoot residue retention impacts microbial-derived C under different soil fertility conditions remains elusive. Here, we conducted a 500-d in situ experiment using Alfisols with low fertility (LF) and high fertility (HF) amended with maize root or shoot (both stem and leaf) residues. The microbial residues (amino sugar biomarkers) and microbial communities (lipid biomarkers) were analyzed at 60, 90, 150, and 500 d after the amended materials were added. The results showed that shoot residue input facilitated microbial residue accumulation more efficiently than root input before 150 d. However, at the end of the experiment, the treatment containing added root residue accumulated more microbial residues and produced a higher proportion of microbial residue in SOC, compared with shoot treatment. These results provide novel evidence that root residue can also yield SOC efficiently through the organic substrate–microbial anabolism pathway, but it depends on the decomposition period. Moreover, soil fertility plays an important role in regulating the quantity and relative composition of microbial residues. Specifically, crop residue application greatly increased the contribution of microbial residue C to SOC in the LF treatment compared to that in the HF treatment on day 500. Meanwhile, crop residue addition had a more positive effect on fungal residue accumulation in the LF soil, while it facilitated the accumulation of bacterial residue in the HF soil. These findings highlight that crop residue addition (especially root residue) is an effective approach for improving microbial-derived C sequestration in infertile soils.

Understanding the temporal changes of soil organic C (SOC) pools and microbial residues is essential for clarifying SOC dynamics in agroecosystems; however, this information remains largely unclear in greenhouse vegetable production (GVP) systems. Here, based on information of SOC pools (i.e., oxidizable organic C pools) and microbial residue C (MRC, as indicated by amino sugars differentiation), a 10-year (2009–2019) field experiment with fertilization was conducted to evaluate how fertilization alters SOC dynamics in a GVP field in Tianjin, China. The experiment includes four treatments (equal N, P2O5, and K2O inputs): 100% chemical N (N100), 50% substitution of chemical N with manure-N (N50M50), straw-N (N50S50), and manure-N plus straw-N (N50M25S25). Results showed that the values of SOC, lability index, and C management index increased and decreased linearly with time in N50M50- and N100-amended soils, respectively, which were mainly induced by the changes in labile C fractions. Based on logistic regression models, we found that these indices in straw-amended soils (N50M25S25 and N50S50) were rapidly increased between 2009 and 2013, and then approach steady levels between 2015 and 2019. These findings suggested that we should guarantee enough C inputs to maintain the level and quality of SOC, otherwise it will cause C loss in the unique GVP soils. Besides, straw-amended treatments increased MRC contents and enlarged their contributions to SOC sequestration, whereas these indices in N100 treatment decreased linearly with the time of fertilization. In conclusion, long-term chemical application alone was not beneficial for SOC accumulation, whereas organic amendments brought several benefits for SOC sequestration in GVP soils. Our results implied that C sequestration in GVP soils is to a large extent determined by the amounts and time of fertilization.

N-Acetylglucosamine-6-phosphate deacetylase (NagA) and glucosamine-6-phosphate deaminase (NagB) are branch point enzymes that direct amino sugars into different pathways. For Staphylococcus aureus NagA, analytical ultracentrifugation and small-angle X-ray scattering data demonstrate that it is an asymmetric dimer in solution. Initial rate experiments show hysteresis, which may be related to pathway regulation, and kinetic parameters similar to other bacterial isozymes. The enzyme binds two Zn2+ ions and is not substrate inhibited, unlike the Escherichia coli isozyme. S. aureus NagB adopts a novel dimeric structure in solution and shows kinetic parameters comparable to other Gram-positive isozymes. In summary, these functional data and solution structures are of use for understanding amino sugar metabolism in S. aureus, and will inform the design of inhibitory molecules.

Withering is an important biological process accompanied by dehydration and cell wall metabolism in postharvest plant organs during curing/processing and storage. However, dynamics involved in cell wall metabolism and resultant water loss during withering in postharvest tobacco leaves is not well-documented. Here, tandem mass tag (TMT)-based quantitative proteomic analysis in postharvest tobacco leaves (cultivar K326) under different withering conditions was performed. In total, 11,556 proteins were detected, among which 496 differentially abundant proteins (DAPs) were identified. To elucidate the withering mechanism of tobacco leaves, 27 DAPs associated with cell wall metabolism were screened. In particular, pectin acetylesterases, glucan endo-1,3-beta-glucosidases, xyloglucan endotransglucosylase/hydrolase, alpha-xylosidase 1-like, probable galactinol-sucrose galactosyltransferases, endochitinase A, chitotriosidase-1-like and expansin were the key proteins responsible for the withering of postharvest tobacco leaves. These DAPs were mainly involved in pectin metabolism, cellulose, hemicellulose and galactose metabolism, amino sugar and nucleotide sugar metabolism as well as cell wall expansion. Furthermore, relative water content and softness values were significantly and positively correlated. Thus, dehydration and cell wall metabolism were crucial for tobacco leaf withering under different conditions. Nine candidate DAPs were confirmed by parallel reaction monitoring (PRM) technique. These results provide new insights into the withering mechanism underlying postharvest physiological regulatory networks in plants/crops.

Mineral nutrient inputs to soil may alter microbial activity and consequently influence the accumulation of microbial residues. In this study, we investigated the effects of application rates and ratios of mineral fertilizers on the microbial residue carbon (MRC) of reddish paddy soils after long-term (15-year) fertilizer applications in southern China. Contents of three soil amino sugars as microbial residue contents were determined and MRC were calculated based on amino sugars. Results showed that three individual amino sugar contents increased as fertilizer application rates increased until maximum values were reached at a rate of 450-59-187 kg ha−1 year−1 (N-P-K). The three amino sugar contents then declined significantly under the highest mineral fertilizer application rate of 675-88-280 kg ha−1 year−1 (N-P-K). In addition, to enhance the microbial residue contents, it was more beneficial to double P (N:P:K = 1:0.26:0.41) in fertilizers applied to the P-deficient reddish paddy soils than to double either N (N:P:K = 2:0.13:0.41) or K (N:P:K = 1:0.13:0.82). The contents of the three individual amino sugars and microbial residues under different fertilizer application rates and ratios were significantly and positively correlated with soil organic carbon (SOC), total N, total P, and pH. Increases in values of the fungal C to bacterial C ratios showed that soil organic matter (SOM) stability increased because of the fertilizer applications over the past 15 years. The contents and ratios of amino sugars can be used as indicators to evaluate the impact of mineral fertilizer applications on SOM dynamics in subtropical paddy soils. The results indicated that fertilizer applications at a rate of 450-59-187 kg ha−1 year−1 (N-P-K) may improve crop yields, SOC contents, and SOC stability in subtropical paddy soils.

Amino sugars are important indices for the contribution of soil microorganisms to soil organic matter. Consequently, the past decade has seen a great increase in the number of studies measuring amino sugars. However, some uncertainties remain in the interpretation of amino sugar data. The objective of the current opinion paper is to summarize current knowledge on amino sugars in soils, to give some advice for future research objectives, and to make a plea for the correct use of information. The study gives an overview on the origin of muramic acid (MurN), glucosamine (GlcN), galactosamine (GalN), and mannosamine (ManN). Information is also provided on measuring total amino sugars in soil but also on compound-specific δ13C and δ15N determination. Special attention is given to the turnover of microbial cell-wall residues, to the interpretation of the GlcN/GalN ratio, and to the reasons for converting fungal GlcN and MurN to microbial residue C. There is no evidence to suggest that the turnover of fungal residues generally differs from that of bacterial residues. On average, MurN contributes 7% to total amino sugars in soil, GlcN 60%, GalN 30%, and ManN 4%. MurN is highly specific for bacteria, GlcN for fungi if corrected for the contribution of bacterial GlcN, whereas GalN and ManN are unspecific microbial markers.