Extracellular Enzymes Research Articles

Phenanthrene degradation by a flavoprotein monooxygenase from Phanerodontia chrysosporium.

Phenanthrene (PHEN), a polycyclic aromatic hydrocarbon (PAH), is degraded by white-rot fungi like Phanerochaete chrysosporium (the fungus has been renamed as Phanerodontia chrysosporium). PHEN is metabolized by P. chrysosporium and transformed into various monohydroxylated and dihydroxylated products. These intermediates are further degraded by cleavage of the aromatic ring. However, the enzymes involved in PHEN conversion in P. chrysosporium remain largely unidentified. We aimed to identify and characterize the P. chrysosporium enzymes involved in the degradation of PHEN and its intermediates. Recombinant P. chrysosporium flavoprotein monooxygenase 11 (FPMO11), a homolog of the salicylate 1-monooxygenase from the naphthalene-degrading bacterium Pseudomonas putida G7, was overexpressed in Escherichia coli. FPMO11 catalyzes the oxidative decarboxylation of 1-hydroxy-2-naphthoate (1H2N) and 2-hydroxy-1-naphthoate (2H1N) to 1,2-dihydroxynaphthalene (1,2DHN). To the best of our knowledge, this is the first study to identify and characterize enzymes with 1H2N and 2H1N monooxygenase activities in members of the FPMO superfamily. Additionally, our search for a dioxygenase with the ability to catalyze the aromatic ring cleavage of 1,2DHN led to the identification of intradiol dioxygenase (IDD) 1 and IDD2 from P. chrysosporium, which catalyzes the ring cleavage of 1,2DHN. Thus, this study also identified, for the first time, intradiol 1,2DHN dioxygenase activity in members of the IDD superfamily. The findings highlight the unique substrate spectra of FPMO11 and IDDs, rendering them attractive candidates for biotechnological applications, especially mitigation of environmental and health risks associated with PAH pollution.IMPORTANCEPhenanthrene (PHEN), a polycyclic aromatic hydrocarbon (PAH), is a widely studied pollutant in environmental science and toxicology due to its presence in fossil fuels, tobacco smoke, and as a byproduct of incomplete combustion processes. White-rot fungi like P. chrysosporium can degrade PHEN through the production of extracellular oxidative enzymes. We investigated the properties of PHEN-degrading enzymes in P. chrysosporium, specifically one flavoprotein monooxygenase (FPMO11) and two intradiol dioxygenases (IDD1 and IDD2). Our findings indicate that the enzymes catalyze the aromatic ring cleavage of PHEN, using the intermediates as substrates, transforming them into less harmful and more biodegradable compounds. This could help reduce environmental pollution and mitigate health risks associated with PAH exposure. The potential of these enzymes for biotechnological applications is also highlighted, emphasizing their critical role in understanding PAH degradation by white-rot fungi.

Extracellular hydrolytic enzyme activities and biofilm formation in Candida species isolated from people living with human immunodeficiency virus with oropharyngeal candidiasis at HIV/AIDS clinics in Uganda.

Commensal oral Candida species can become opportunistic and transition to pathogenic causes of oropharyngeal candidiasis (OPC) in individuals with impaired immunity through ecological cues and the expression of extracellular hydrolytic enzyme activities and biofilm formation. We evaluated phospholipase, proteinase, hemolysin, esterase, and coagulase enzymatic activities and biofilm formation in Candida species isolated from people living with human immunodeficiency virus (PLHIV) with OPC. Thirty-five Candida isolates from PLHIV with OPC were retrieved from a sample repository and evaluated for phospholipase activity using the egg yolk agar method, proteinase activity using the bovine serum albumin agar method, hemolysin activity using the blood agar plate method, esterase activity using the Tween 80 opacity test medium method, coagulase activity using the classical tube method, and biofilm formation using the microtiter plate assay method in vitro. A total of 35 Candida isolates obtained from PLHIV with OPC were included in this study, and phospholipase and proteinase activities were detected in 33/35 (94.3%) and 31/35 (88.6%) Candida isolates, respectively. Up to 25/35 (71.4%) of the Candida isolates exhibited biofilm formation, whereas esterase activity was demonstrated in 23/35 (65.7%) of the Candida isolates. Fewer isolates (21/35, 60%) produced hemolysin, and coagulase production was the least common virulence activity detected in 18/35 (51.4%) of the Candida isolates. Phospholipase and proteinase activities were the strongest in oropharyngeal Candida species.

Drought and vegetation restoration patterns shape soil enzyme activity and nutrient limitation dynamics in the loess plateau.

Appropriate vegetation restoration measures are beneficial to ecosystem restoration and nutrient retention in ecologically fragile areas. However, the high water consumption of planted forests and the increasing frequency of drought events may reshape or complicate this ecological process. The effects of forest types and drought stress on nutrient limitation remain unclear. In this study, we selected five different vegetation restoration types on the Loess Plateau, China, and applied three drought levels to assess their effects on extracellular enzyme activity, soil microbial biomass, and soil nutrient limitations.We measured the activities of carbon-, nitrogen-, and phosphorus-acquiring enzymes and investigated the relationships among enzyme activity, microbial biomass, and nutrient limitations under drought conditions. Our results showed that vegetation types and drought significantly influenced soil enzymatic activity and stoichiometry. Mixed forests demonstrated higher enzyme activity and nutrient content compared to pure forests, indicating greater resilience under drought conditions. Short-term drought significantly reduced soil enzyme activity and microbial biomass, whereas mild drought stimulated enzyme activity, and moderate drought promoted microbial biomass. Drought markedly decreased microbial carbon and nitrogen content but increased the microbial carbon-to-nitrogen ratio. Furthermore, drought enhanced the correlation between microbial biomass carbon and carbon-acquiring enzymes, but there was no correlation between microbial biomass nitrogen and nitrogen-acquiring enzymes under drought. All vegetation types exhibited nitrogen limitation, and a negative correlation was observed between nitrogen and carbon limitations under drought conditions. Drought significantly exacerbated nitrogen limitation, while its impact on carbon limitation varied with drought severity and vegetation type. Overall, plant communities exhibited distinct nutrient acquisition strategies under drought stress, resulting in complex changes in soil enzyme activities and microbial biomass. This study advances our understanding of microbial nutrient limitations and enzymatic activities under varying vegetation restoration patterns and drought conditions, providing critical insights for enhancing soil resilience and nutrient cycling under climate change.

Strong Effects of Increased Hydrostatic Pressure on Polysaccharide‐Hydrolyzing Enzyme Activities in Coastal Seawater and Sediments

AbstractHeterotrophic microorganisms are responsible for transforming and respiring a substantial fraction of the organic matter produced by phytoplankton in the surface ocean. Much of this organic matter is composed of polysaccharides, high‐molecular weight (HMW) sugars. To initiate degradation of polysaccharides, microorganisms must produce extracellular enzymes of the right structural specificity to hydrolyze these complex structures. To date, most measurements of enzyme activities are made at in situ temperatures, but at atmospheric pressure. However, previous studies have shown that hydrostatic pressure can impact the functionality of enzymes. Since deep sea communities may be seeded by microbes from shallow waters, we aimed to determine if pressure affects the performance of enzymes from coastal waters. To determine the extent to which enzymatic activities of coastal microbial communities are affected by pressure, we quantified the degradation of seven polysaccharides under pressures ranging from 0.1 MPa (atmospheric) to 40 MPa (equivalent to 4,000 m). Enzyme activities of pelagic communities were inhibited with increased pressure, while enzyme activities of benthic microbial communities were more resistant to increased pressure. Addition of HMW organic matter resulted in communities with enzyme activities that were more resistant to increased pressure. However, the freely‐dissolved enzymes (<0.2 μm) produced by these communities were strongly inhibited by increased hydrostatic pressure, suggesting that the pressure‐resistant enzymes were cell‐surface attached. Because pressure inhibition of enzyme activities varied strongly by polysaccharide, we surmise that the structural complexity of a polysaccharide—and therefore the number of distinct enzymes required for hydrolysis—is likely closely associated with pressure inhibition.

Priority Effect of Endophyte Community in Newly Fallen Leaves of Quercus acutissima Carruth. on Litter Decomposition and Saprotrophic Microbial Community

This study examines the role of endophytic microbial colonization on the decomposition of oak leaf litter, a high-quality substrate in forest ecosystems. Over a one-year incubation, we observed a significant reduction in mass loss in colonized litter (46%) compared to non-colonized litter (80%), indicating an inhibitory effect of endophytes on decomposition. Structural equation modeling revealed a bimodal impact of endophytic microbes, with an initial enhancement followed by a pronounced inhibition as decomposition progressed. Extracellular enzyme stoichiometry showed phosphorus limitation became significant, particularly with endophytic colonization, contributing to reduced decomposition rates. Microbial diversity analyses exposed the variable impacts of endophytic colonization on fungal and bacterial communities, with taxa such as Helotiales (order) and Burkholderia–Caballeronia–Paraburkholderia (genus) significantly affected. The identification of 16 keystone species, mostly endophytic bacteria, underscored their pivotal influence on decomposition processes. Despite initial endophytic impacts, abundant carbon resources promoted stochastic colonization, potentially surpassing the effects of early endophytic establishment. This study provides insights into the priority effects of endophytic colonization and niche differentiation, offering a foundation for further research into the mechanisms underlying these processes and their ecological consequences in various ecosystems.

Lack of ST2 aggravates glioma invasiveness, vascular abnormality and immune suppression

Abstract Background Glioblastoma (GBM) is the most common primary malignant brain tumor in adults, characterized by aggressive growth and a dismal prognosis. Interleukin-33 (IL-33) and its receptor ST2 have emerged as regulators of glioma growth, but their exact function in tumorigenesis have not been deciphered. Indeed, previous studies on IL-33 in cancer have yielded somewhat opposing results as to whether it is pro- or anti-tumorigenic. Methods IL-33 expression was assessed in a GBM tissue microarray and public databases. As in vivo models we used orthotopic xenografts of patient-derived GBM cells, and syngenic models with grafted mouse glioma cells. Results We analyzed the role for IL-33 and its receptor ST2 in non-malignant cells of the glioma microenvironment and find that IL-33 levels are increased in cells surrounding the tumor. Protein complexes of IL-33 and ST2 are mainly found outside of the tumor core. The IL-33-producing cells consist primarily of oligodendrocytes. To determine the function for IL-33 in the tumor microenvironment, we used mice lacking the ST2 receptor. When glioma cells were grafted to ST2-deficient mouse brains, the resulting tumors exhibit a more invasive growth pattern, and are associated with poorer survival, compared to wild-type mice. Tumors in ST2-deficient hosts are more invasive, with increased expression of extracellular matrix remodeling enzymes and enhanced tumor angiogenesis. Furthermore, the absence of ST2 leads to a more immunosuppressive environment. Conclusions Our findings reveal that glia-derived IL-33 and its receptor ST2 participates in modulating tumor invasiveness, tumor vasculature and immunosuppression in glioma.

Varying effects of Vicia sativa and Vicia villosa on bacterial composition and enzyme activities in nutrient-deficient sugarcane soils under greenhouse conditions

Declining soil health and productivity are key challenges faced by sugarcane small-scale growers in South Africa. Incorporating Vicia sativa and Vicia villosa as cover crops can improve soil health by enhancing nutrient-cycling enzyme activities and nitrogen (N) contributions while promoting the presence of beneficial bacteria in the rhizosphere. A greenhouse experiment was conducted to evaluate the chemical and biological inputs of V. sativa and V. villosa in nutrient-deficient, KwaZulu-Natal (KZN) sugarcane plantation soils. The nutrient concentrations, N and phosphorus (P) cycling bacteria, and extracellular enzyme activities of 5 soils were determined pre-planting and post-V. sativa and V. villosa harvest. Post-harvesting soils had higher pH levels than pre-planting soils. The number of plant growth-promoting rhizobacteria increased post-V. sativa and V. villosa harvest, with Arthrobacter, Burkholderia, Paraburkholderia and Pseudomonas as the dominant genera. Acid phosphatase and glucosidase activities increased, with Mvutshini and Mzinto showing the most significant increases (phosphatase: 18.66 to 84.67 for V. villosa, 90.33 for V. sativa; glucosidase: 15.33 to 83 for V. villosa and 105 µmolh− 1g− 1 for V. sativa). In conclusion, V. sativa and V. villosa increased PGPR, pH and enzyme activities, making them viable cover crops for nutrient-deficient sugarcane soils.

Microbiota Involved in the Degradation of Tremella fuciformis Polysaccharide and Microbial Enzymatic Potential Revealed by Microbiome and Metagenome

Tremella fuciformis, as a traditional edible fungus in Asian countries, is rich in polysaccharides with a variety of bioactivities. Nevertheless, its high molecular weight and complex structure have caused limitations in its application and structural analysis. In this study, we successfully screened a Tremella fuciformis polysaccharide-degrading bacterium from the soil by enriching and screening. The mixed bacterium consisted mainly of Verrucomicrobium (55.4%) and Lysobacter (43.8%), which released extracellular enzymes that enabled the degradation of Tremella fuciformis polysaccharides. The functional annotation using microbiome and metagenome combined with bioinformatics revealed its active carbohydrate metabolism, binding, and catalysis. It exposed the enzymatic potential of the bacterium and provided a basis for the exploration of hydrolytic enzymes for hardly degradable polysaccharides in fungi.

Fabrication of Multifunctional Three-Component Supramolecular Nano-Biscuits via Two Macrocycles-Involved Self-Assembly for Rice, Citrus and Kiwifruit Protections.

Bacterial plant diseases, worsened by biofilm-mediated resistance, are increasingly threatening global food security. Numerous attempts have been made to develop agrochemicals that inhibit biofilms, however, their ineffective foliar deposition and difficulty in removing mature biofilms remain major challenges. Herein, multifunctional three-component supramolecular nano-biscuits (NI6R@CB[7]@β-CD) are successfully engineered via ordered self-assembly between two macrocycles [cucurbit[7]uril (CB[7]), β-cyclodextrin (β-CD)] and (R)-2-naphthol-based bis-imidazolium bromide salt (NI6R). This macrocycles-involved bactericidal material combines many advantages. 1) Alleviate the off-target movement of droplets on hydrophobic blade surfaces. 2) Enhance the biofilm-disrupting ability. At a low-dose of 4.44µg mL-1, the inhibition rate of biofilm formation reached 78.3%. At 35.5µg mL-1, the potency to remove mature biofilms reached 77.6%. 3) Efficiently hinder bacterial reproduction, swimming, extracellular polysaccharide production, extracellular enzyme secretion, and virulence to plants. These superior characteristics are undoubtedly transmitted to the in vivo control effect. At 200µg mL-1, this smart material exhibits superior control efficiencies of 49.6%/65.0%/85.4% against three kinds of bacterial diseases (rice leaf blight, citrus canker, and kiwifruit canker), respectively, surpassing the commercial bactericide-thiodiazole-copper-20%SC (33.6%/41.5%/43.2%) and NI6R (40.3%/51.2%/71.2%). Furthermore, NI6R@CB[7]@β-CD is biosafe to non-target organisms. This study is instructive for constructing multifunctional agrochemicals in sustainable crop protection.

Legumes reduce the effects of salt stress on co-existing grass.

Nitrogen (N) fixing legumes typically enhance the ability of coexisting non-N-fixing species to resist disease and drought, but whether legumes enhance their ability to resist salt stress remains unknown, restricting our ability to explore the potential of legumes to rehabilitate salt-affected ecosystems. We conducted a simulation experiment to examine whether and how legumes influence the response of coexisting grass to salt stress. We compared the effects of salt stress on the plant biomass, root cell viability, antioxidant enzyme activities, soil extracellular enzyme activities and microbial functional gene abundances associated with N and phosphorus (P) cycling between pure grass communities and legume-grass mixtures. We found that salt stress decreased grass biomass and the abundance of most N and P cycling genes in rhizosphere soils. However, these negative effects were smaller in legume-grass mixtures than in pure grass community. Additionally, salt stress increased the activities of soil N and P cycling enzymes, with greater positive effects observed in legume-grass mixtures than in the pure grass community. The structural equation modelling results showed that the most direct and indirect path coefficients of salt stress effects on biomass were smaller in legume-grass mixtures than in the pure grass community. Our findings provide direct evidence that legumes can reduce the negative impact of salt stress on co-existing grass community, highlighting the potential of including legumes with high N fixation abilities to restore salt-affected ecosystems.

A climatically significant abiotic mechanism driving carbon loss and nitrogen limitation in peat bogs

Sphagnum-dominated bogs are climatically impactful systems that exhibit two puzzling characteristics: CO2:CH4 ratios are greater than those predicted by electron balance models and C decomposition rates are enigmatically slow. We hypothesized that Maillard reactions partially explain both phenomena by increasing apparent CO2 production via eliminative decarboxylation and sequestering bioavailable nitrogen (N). We tested this hypothesis using incubations of sterilized Maillard reactants, and live and sterilized bog peat. Consistent with our hypotheses, CO2 production in the sterilized peat was equivalent to 8–13% of CO2 production in unsterilized peat, and the increased formation of aromatic N compounds decreased N-availability. Numerous sterility assessments rule out biological contamination or extracellular enzyme activity as significant sources of this CO2. These findings suggest a need for a reevaluation of the fixed CO2:CH4 production ratios commonly used in wetland biogeochemical models, which could be improved by incorporating abiotic sources of CO2 production and N sequestration.

Impact of short-term pasture development on soil aggregation, temperature sensitivity of soil organic carbon, and functional diversity in semi-arid ecosystem

Pasture development could be a viable option to restore degraded land in semi-arid region. New knowledge on soil functional diversity, aggregation, and temperature sensitivity (Q 10) of soil organic carbon (SOC) after pasture development would assist to accomplish the scope of global pastureland management for climate change mitigation and land restoration. To understand the impact of pasture development on soil aggregation, SOC stock, and its Q 10, research was undertaken at three development sites (RS1, RS2, RS3) in India with seeding of Cenchrus ciliaris, Megathyrus maximus, and Stylosanthes seabrana (at a line-ratio of 2:2:1). After three years, biomass productivity and for SOC, aggregation, enzyme activities, etc. at 0–20 and 21–40 cm depths were estimated. Pasture development improved biomass productivity from 0.68 mg ha−1 in undeveloped site to 3.62–4.64 mg ha−1. Pasture development enhanced SOC stock from 5.85 to 7.31 mg C ha−1 at the surface layer with an annual accumulation rate of 28–112 kg SOC ha−1 year−1. Greater activities of extracellular enzymes were observed at the surface soil layer in pasture development sites over undeveloped control. The mean weight diameter was ∼23–38% higher at pasture development sites over undeveloped sites. The Q 10 being controlled by the labile carbon was significantly higher (13–29%) at the pasture development sites over undeveloped site. Hence, short-term pasture development could improve the SOC stocks at the surface layer only, but the stocks were vulnerable to C loss at higher temperature. However, long-term pasture development could have a great potential to accrue C to mitigate climate change.

Molecular Characterization and Plant Growth Promotion Potential of Paenibacillus Dendritiformis Endophyte Isolated from Tecomella Undulata (Roheda)

In this study, we have isolated a bacterial endophyte Paenibacillus dendritiformis strain RAE13 (Accession number: OR259131) from the leaves of Tecomella undulata (Roheda) plant. The identification of bacterial species was carried out using 16s-rDNA ribotyping. Subsequently, the isolated bacterial strain was gauged for its potential to endorse plant growth through various mechanisms such as nitrogen fixation, IAA production, HCN synthesis, siderophore generation, and ammonia production. Furthermore, the evaluation focused on the endophyte's capacity for producing extracellular enzymes, including cellulase, chitinase, protease, amylase, and catalase. The endophyte exhibited to synthesize an average of 18±0.375 μg/ml of indole-3-acetic acid (IAA) after being subjected to a concentration of 5 mg/ml of tryptophan over a 14-day incubation period. The endophytic isolate RAE 13 produced an average of 42.4±0.004 μg/ml of Gibberellin, solubilized phosphate in the range of 70.2 μg/ml to 135.5 μg/ml, and produced an average of 45.5 μg/ml of ammonia. The phylogenetic analysis unveiled that the isolated strain RAE13 had a common ancestor and had a maximum nucleotide sequence similarity of 98.30% with Paenibacillus sp isolates of Uttar Pradesh, India. To diminish the consumption of chemicals in conventional farming, the results indicated that the isolated endophyte had great potential as a plant growth-stimulating inoculant. Henceforward, utilization of these extracellular enzymes for medical and industrial applications will be highly beneficial. Additionally, it could enhance plant tolerance to challenging environmental circumstances including drought and high temperatures.

Identifying a Biocontrol Bacterium with Disease-Prevention Potential and Employing It as a Powerful Biocontrol Agent Against Fusarium oxysporum.

Biocontrol microbes are environment friendly and safe for humans and animals. To seek biocontrol microbes effective in suppressing Fusarium oxysporum is important for tomato production. F. oxysporum is a soil-borne pathogen capable of causing wilt in numerous plant species. Therefore, we found a biocontrol bacterium with an excellent control effect from the rhizosphere soil of plant roots. In this work, we focus on two parts of work. The first part is the identification and genomic analysis of the biocontrol bacterium Y-4; the second part is the control efficiency of strain Y-4 on F. oxysporum. For this study, we identified strain Y-4 as Bacillus velezensis. It is an aerobic Gram-positive bacterium that can secrete a variety of extracellular enzymes and siderophores. Strain Y-4 also contains a large number of disease-resistant genes and a gene cluster that forms antibacterial substances. In addition, we found that it significantly inhibited the reproduction of F. oxysporum in a culture dish. In the indoor control effect test, after treatment with strain Y-4 suspension, the disease index of tomato plants decreased significantly. Furthermore, the control efficiency of the plants was 71.88%. At the same time, Y-4 bacterial suspension induced an increase in POD and SOD enzyme activities in tomato leaves, resulting in increased plant resistance. Taken together, strain Y-4 proves to be an effective means of controlling F. oxysporum in tomatoes.

Plant Colonization by Biocontrol Bacteria and Improved Plant Health: A Review.

The use of biological control agents is one of the best strategies available to combat the plant diseases in an ecofriendly manner. Biocontrol bacteria capable of providing beneficial effect in crop plant growth and health, have been developed for several decades. It highlights the need for a deeper understanding of the colonization mechanisms employed by biocontrol bacteria to enhance their efficacy in plant pathogen control. The present review deals with the in-depth understanding of steps involved in host colonization by biocontrol bacteria. The colonization process starts from the root zone, where biocontrol bacteria establish initial interactions with the plant's root system. Moving beyond the roots, biocontrol bacteria migrate and colonize other plant organs, including stems, leaves, and even flowers. Also, the present review attempts to explore the mechanisms facilitating bacterial movement within the plant such as migrating through interconnected spaces such as vessels or in the apoplast, and applying quorum sensing or extracellular enzymes during colonization and what is needed to establish a long-term association within a plant. The impacts on microbial community dynamics, nutrient cycling, and overall plant health are discussed, emphasizing the intricate relationships between biocontrol bacteria and the plant's microbiome and the benefits to the plant's above-ground parts, the biocontrol 40 bacteria confer. By unraveling these mechanisms, researchers can develop targeted strategies for enhancing the colonization efficiency and overall effectiveness of biocontrol bacteria, leading to more sustainability and resilience.

Influence of Arbuscular Mycorrhizal Fungi on Nitrogen Dynamics During Cinnamomum camphora Litter Decomposition.

Arbuscular mycorrhizal fungi (AMF) can preferentially absorb the released ammonium (NH4+) over nitrate (NO3-) during litter decomposition. However, the impact of AMF's absorption of NH4+ on litter nitrogen (N) decomposition is still unclear. In this study, we investigated the effects of AMF uptake for NH4+ on litter N metabolic characteristics by enriching NH4+ via AMF suppression and nitrification inhibition in a subtropical Cinnamomum camphora forest. The results showed that AMF suppression and nitrification inhibition significantly decelerated litter decomposition in the early stage due to the repression of NH4+ in extracellular enzyme activity. In the late stage, when soil NH4+ content was low, in contrast, they promoted litter decomposition by increasing the extracellular enzyme activities. Nitrification inhibition mainly promoted the utilization of plant-derived N by promoting the degradation of the amide I, amide II, and III bands by increasing protease activity, and it promoted ammonification by increasing urease activities, whereas it reduced the utilization of microbial-derived N by decreasing chitinase activity. On the contrary, AMF suppression, which significantly reduced the ammonification rate and increased the nitrification rate, only facilitated the degradation of the amide II band. Moreover, it intensified the microbial-derived N decomposition by increasing chitinase activity. The degradation of the amide I and II bands still relied on the priming effects of AMF on soil saprotrophs. This was likely driven by AMF-mediated phosphorus (P) mineralization. Nutrient acquiring, especially P by phosphatase, were the main factors in predicting litter decomposition and protein degradation. Thus, AMF could relieve the end-product repression of locally enriched NH4+ in extracellular enzyme activity and promote early-stage litter decomposition. However, the promotive effects of AMF on litter protein degradation and NH4+ release rely on P mineralization. Our results demonstrated that AMF could alleviate the N limitation for net primary production via accelerating litter N decomposition and reducing N loss. Moreover, they could restrict the decomposition of recalcitrant components by competing with saprotrophs for nutrients. Both pathways will contribute to C sequestration in forest ecosystems, which advances our understanding of AMF's contribution to nutrient cycling and ecosystem processes in subtropical forests.

Long-term climate establishes functional legacies by altering microbial traits.

Long-term climate history can influence rates of soil carbon cycling but the microbial traits underlying these legacy effects are not well understood. Legacies may result if historical climate differences alter the traits of soil microbial communities, particularly those associated with carbon cycling and stress tolerance. However, it is also possible that contemporary conditions can overcome the influence of historical climate, particularly under extreme conditions. Using shotgun metagenomics, we assessed the composition of soil microbial functional genes across a mean annual precipitation gradient that previously showed evidence of strong climate legacies in soil carbon flux and extracellular enzyme activity. Sampling coincided with recovery from a regional, multi-year severe drought, allowing us to document how the strength of climate legacies varied with contemporary conditions. We found increased investment in genes associated with resource cycling with historically higher precipitation across the gradient, particularly in traits related to resource transport and complex carbon degradation. This legacy effect was strongest in seasons with the lowest soil moisture, suggesting that contemporary conditions-particularly, resource stress under water limitation-influences the strength of legacy effects. In contrast, investment in stress tolerance did not vary with historical precipitation, likely due to frequent periodic drought throughout the gradient. Differences in the relative abundance of functional genes explained over half of variation in microbial functional capacity-potential enzyme activity-more so than historical precipitation or current moisture conditions. Together, these results suggest that long-term climate can alter the functional potential of soil microbial communities, leading to legacies in carbon cycling.

Nonlinear response of soil organic carbon sequestration to deadwood decomposition in a subtropical–temperate ecotonal forest

Abstract The decomposition of deadwood is a crucial process for the accumulation and sequestration of soil organic carbon (SOC) in forest ecosystems. Yet, the response of SOC to various classes of deadwood decay and the underlying mechanisms remain unclear. Here, we investigated the dynamics of SOC, soil properties, extracellular enzyme activities, and phospholipid fatty acid biomarkers across five decay classes (defined from 1 to 5) of Masson pine (Pinus massoniana Lamb.) downed deadwood in a subtropical-temperate ecotone forest in Central China. Results showed a nonlinear response pattern of SOC along the deadwood decomposition gradient, with the maximum value at the decay class 4. Soil available nitrogen content, bacterial biomass, fungal biomass, the ratio of fungal to bacterial biomass, cellulase, and ligninase all increased, whereas soil pH decreased along with the intensification of deadwood decay. Increases in SOC content were associated with a direct positive effect of bacteria, and direct and indirect positive effects of fungi via cellulase, but ligninase showed no significant relationship with SOC content. These findings suggest that cellulose and microbial biomass determine soil C formation and sequestration during deadwood decomposition. This study highlights the importance of the nonlinear response of SOC to deadwood decay intensification, thus helping to predict future C–climate feedbacks.

Biochemical characterization, Oxidative Stress and Antifungal Susceptibility in Acremonium sclerotigenum

Acremonium is a polyphyletic genus known as cephalosporium formerly widely spread in environment commonly found in soil, decaying vegetation, plant debris and decaying food. Acremonium sclerotigenum isolated from clinical samples of tinea infected patients from Punjab Pakistan. Goal of the study is to achieve biochemical characterization of the A.sclerotigenum and to analyze the effect of physiological stress and terbinafine susceptibility in test strain. A.sclerotigenum was analyzed for oxidative, osmotic stress adaptability by culture characteristics, protease and lipase qualitative and activity assays and antifungal terbinafine susceptibility testing for isolated Acremonium strain. Study revealed that A.sclerotigenum is not resistant to osmotic and oxidative stress. Level of extracellular proteolytic enzymes is low although lipase enzyme found to be active at a moderate level. A.sclerotigenum has very low MIC for terbinafine. A detailed research on the mechanism involving in anti-fungal resistance in A.sclerotigenum, is still to be explore.

Aeration promotes Proteobacteria over Firmicutes in macerated food waste, resulting in superior anaerobic digestion efficiency.

Aeration is a common pretreatment method to enhance biogas production via anaerobic digestion of waste organic feedstocks such as unused food. While impacts on downstream anaerobic digestion have been intensively investigated, the consequence of aeration on the microbial community in food waste has not been characterized. Food waste has a low pH resulting from the dominance of lactic acid bacteria within the Firmicutes phylum. This excludes other phylotypes with a higher potential to hydrolyse complex biopolymers in food waste. In this study, we reveal that aeration of macerated food waste results in a dramatic shift away from Firmicutes towards dominance of Proteobacteria that are better known for extracellular enzyme production. Given that hydrolysis is the rate limiting step in anaerobic digestion, this explains why aeration improves the efficiency of biogas production from food waste. The discovery that Proteobacteria dominate microbial communities in aerated food waste opens up opportunities to manipulate extracellular enzyme production through gene expression mechanisms common among Proteobacteria such as quorum sensing.