Shy is a proteobacterial steroid hydratase which catalyzes steroid side chain degradation without requiring a catalytically inert partner domain.

Shy (side chain hydratase) and Sal (side chain aldolase), are involved in successive reactions in the pathway of bile acid side chain catabolism in Proteobacteria. Untagged Shy copurified with His-tagged Sal indicating that the two enzymes form a complex. Shy contains a MaoC and a DUF35 domain. When coexpressed with Sal, the DUF35 domain but not the MaoC domain of Shy was observed to copurify with Sal, indicating Sal interacts with Shy through its DUF35 domain. The MaoC domain of Shy (ShyMaoC) remained catalytically viable and could hydrate cholyl-enoyl-CoA with similar catalytic efficiency as in the Shy-Sal complex. Sal expressed with the DUF35 domain of Shy (Sal-ShyDUF35) was similarly competent for the retro-aldol cleavage of cholyl-3-OH-CoA. ShyMaoC showed a preference for C5 side chain bile acid substrates, exhibiting low activity toward C3 side chain substrates. The ShyMaoC structure was determined by X-ray crystallography, showing a hot dog fold with a short central helix surrounded by a twisted antiparallel ß-sheet. Modeling and mutagenesis studies suggest that the bile acid substrate occupies the large open cleft formed by the truncated central helix and repositioning of the active site housing. ShyMaoC therefore contains two substrate binding sites per homodimer, making it distinct from previously characterized MaoC steroid hydratases that are (pseudo) heterodimers with one substrate binding site per dimer. The characterization of Shy provides insight into how MaoC family hydratases have adapted to accommodate large polycyclic substrates that can facilitate future engineering of these enzymes to produce novel steroid pharmaceuticals.

Zebrafish maoc1 Attenuates Spring Viremia of Carp Virus Propagation by Promoting Autophagy-Lysosome-Dependent Degradation of Viral Phosphoprotein.

Spring viremia of carp virus (SVCV) is the causative agent of spring viremia of carp (SVC), an important infectious disease that causes high mortality in aquaculture cyprinids. How the host defends against SVCV infection and the underlying mechanisms are still elusive. In this study, we identify that a novel gene named maoc1 is induced by SVCV infection. maoc1-deficient zebrafish are more susceptible to SVCV infection, with higher virus replication and antiviral gene induction. Further assays indicate that maoc1 interacts with the P protein of SVCV to trigger P protein degradation through the autophagy-lysosomal pathway, leading to the restriction of SVCV propagation. These findings reveal a unique zebrafish defense machinery in response to SVCV infection. IMPORTANCE SVCV P protein plays an essential role in the virus replication and viral immune evasion process. Here, we identify maoc1 as a novel SVCV-inducible gene and demonstrate its antiviral capacity through attenuating SVCV replication, by directly binding to P protein and mediating its degradation via the autophagy-lysosomal pathway. Therefore, this study not only reveals an essential role of maoc1 in fighting against SVCV infection but also demonstrates an unusual host defense mechanism in response to invading viruses.

Changes in soil organic carbon stocks and its physical fractions along an elevation in a subtropical mountain forest.

Soil microorganisms are the drivers of soil organic carbon (SOC) mineralization, and the activities of these microorganisms are considered to play a key role in SOC dynamics. However, studies of the relationship between soil microbial carbon metabolism and SOC stocks are rare, especially in different physical fractions (e.g., particulate organic carbon (POC) fraction and mineral-associated organic carbon (MAOC) fraction). In this study, we investigated the changing patterns of SOC stocks, POC stocks, MAOC stocks and microbial carbon metabolism (e.g., microbial growth, carbon use efficiency and biomass turnover time) at 0-20 cm along an elevational gradient in a subtropical mountain forest ecosystem. Our results showed that SOC and POC stocks increased but MAOC stocks remained stable along the elevational gradient. Soil microbial growth increased while microbial turnover time decreased with elevation. Using structural equation modeling, we found that heightened microbial growth is associated with elevated POC stocks. Moreover, MAOC stocks positively correlate with microbial growth but show negative associations with both POC stocks and soil pH. Overall, the increase in SOC stocks along the elevational gradient is primarily driven by changes in POC stocks rather than MAOC stocks. These findings underscore the importance of considering diverse soil carbon fractions and microbial activities in predicting SOC responses to elevation, offering insights into potential climate change feedbacks.

Cover crop root morphology rather than quality controls the fate of root and rhizodeposition C into distinct soil C pools.

Cover crops increase carbon (C) inputs to agricultural soils, and thus have the potential to mitigate climate change through enhanced soil organic carbon (SOC) storage. However, few studies have explored the fate of belowground C inputs associated with varying root traits into the distinct SOC pools of mineral-associated organic carbon (MAOC) particulate organic carbon (POC). Therefore, a packed 0.5 m column trial was established with 0.25 m topsoil and 0.25 m subsoil with four cover crops species (winter rye, oilseed radish, chicory, and hairy vetch) known to differ in C:N ratio and root morphology. Cover crops were 14 CO2 -labeled for 3 months, and then, half of the columns were sampled to quantify root and rhizodeposition C. In the remaining columns, plant shoots were harvested and the undisturbed soil and roots were left for incubation. Bulk soil from both sampling times was subjected to a simple fractionation scheme, where 14 C in the <50 and >50 µm fraction was assumed to represent MAOC and POC, respectively. The fast-growing rye and radish produced the highest root C. The percentage loss of C via rhizodeposition (%ClvR) showed a distinct pattern, with 22% for the more branched roots (rye and vetch) and 6%-8% for the less branched roots (radish and chicory). This suggests that root morphology plays a key role in determining rhizodeposition C. After 1 year of incubation at room temperature, the remaining MAOC and POC were positively correlated with belowground inputs in absolute terms. However, topsoil MAOC formation efficiencies (cover crop-derived MAOC remaining as a share of belowground inputs) were higher for vetch and rye (21% and 15%, respectively) than for chicory and radish (9% and 10%, respectively), suggesting a greater importance of rhizodeposition (or indirectly, root morphology) than solely substrate C:N ratio for longer term C stabilization.

Critical range of soil organic carbon in southern Europe lands under desertification risk.

Soil quality is fundamental for ecosystem long term functionality, productivity and resilience to current climatic changes. Despite its importance, soil is lost and degraded at dramatic rates worldwide. In Europe, the Mediterranean areas are a hotspot for soil erosion and land degradation due to a combination of climatic conditions, soils, geomorphology and anthropic pressure. Soil organic carbon (SOC) is considered a key indicator of soil quality as it relates to other fundamental soil functions supporting crucial ecosystem services. In the present study, the functional relationships among SOC and other important soil properties were investigated in the topsoil of 38 sites under different land cover and management, distributed over three Mediterranean regions under strong desertification risk, with the final aim to define critical SOC ranges for fast loss of important soil functionalities. The study sites belonged to private and public landowners seeking to adopt sustainable land management practices to support ecosystem sustainability and productivity of their land. Data showed a very clear relationship between SOC concentrations and the other analyzed soil properties: total nitrogen, bulk density, cation exchange capacity, available water capacity, microbial biomass, C fractions associated to particulate organic matter and to the mineral soil component and indirectly with net N mineralization. Below 20 g SOC kg-1, additional changes of SOC concentrations resulted in a steep variation of all the analyzed soil indicators, an order of magnitude higher than the changes occurring between 50 and 100 g SOC kg-1 and 3-4 times the changes observed at 20-50 g SOC kg-1. About half of the study sites showed average SOC concentration of the topsoil centimetres <20 g SOC kg-1. For these areas the level of SOC might hence be considered critical and immediate and effective recovery management plans are needed to avoid complete land degradation in the next future.

Meta-analysis protocol on the effects of cover crops on pool specific soil organic carbon.

Soil organic carbon (SOC) plays an important role in agricultural soils, as it contributes to overall soil health as well as climate change mitigation and adaptation. By conducting a meta-analysis, we aim to quantitatively summarize research studying the effects of cover crops (CC) on SOC pools throughout soil depths in arable cropland. We included global studies located in the climatic zones present in Europe. The pools chosen for this analysis are the particulate organic carbon (POC) and the mineral associated organic carbon (MAOC) and the microbial biomass carbon (MBC). Alongside, we will study the effects of a broad range of moderators, such as pedo-climatic factors, other agricultural management practices and CC characteristics e.g., type. We identified 71 relevant studies from 61 articles, of which mean values for SOC pools, standard deviations and sample sizes for treatments (CC) and controls (no CC) were extracted. To perform the meta-analysis, an effect size will be calculated for each study, which will then be summarized across studies by using weighing procedure. Consequently, this meta-analysis will provide valuable information on the state of knowledge on SOC pool change influenced by CC, corresponding quantitative summary results and the sources of heterogeneity influencing these results.

Nitrate as an alternative electron acceptor destabilizes the mineral associated organic carbon in moisturized deep soil depths.

Numerous studies have investigated the effects of nitrogen (N) addition on soil organic carbon (SOC) decomposition. However, most studies have focused on the shallow top soils <0.2 m (surface soil), with a few studies also examining the deeper soil depths of 0.5-1.0 m (subsoil). Studies investigating the effects of N addition on SOC decomposition in soil >1.0 m deep (deep soil) are rare. Here, we investigated the effects and the underlying mechanisms of nitrate addition on SOC stability in soil depths deeper than 1.0 m. The results showed that nitrate addition promoted deep soil respiration if the stoichiometric mole ratio of nitrate to O2 exceeded the threshold of 6:1, at which nitrate can be used as an alternative acceptor to O2 for microbial respiration. In addition, the mole ratio of the produced CO2 to N2O was 2.57:1, which is close to the theoretical ratio of 2:1 expected when nitrate is used as an electron acceptor for microbial respiration. These results demonstrated that nitrate, as an alternative acceptor to O2, promoted microbial carbon decomposition in deep soil. Furthermore, our results showed that nitrate addition increased the abundance of SOC decomposers and the expressions of their functional genes, and concurrently decreased MAOC, and the ratio of MAOC/SOC decreased from 20% before incubation to 4% at the end of incubation. Thus, nitrate can destabilize the MAOC in deep soils by stimulating microbial utilization of MAOC. Our results imply a new mechanism on how above-ground anthropogenic N inputs affect MAOC stability in deep soil. Mitigation of nitrate leaching is expected to benefit the conservation of MAOC in deep soil depths.

[Soil Organic Carbon Storage, Active Component Contents, and Stability Along a Flooding Gradient in the Tidal Wetland of the Jiulong River Estuary].

Flooding is one of the key environmental factors affecting the carbon sequestration potential of estuarine tidal flat wetlands. In order to reveal the effect of flooding on soil carbon (C) sinks in estuarine tidal wetlands, we investigated and analyzed the soil organic carbon (SOC) storage, the contents of active SOC components, and SOC stability indicators across a tidal flat in the Jiulong River estuary in southeast China. The results showed that the SOC storage gradually decreased by 54% with the increase in flooding frequency. The change pattern of microbial biomass carbon (MBC), dissolved organic carbon (DOC), and liable organic carbon (LOC) followed the change pattern of the SOC storage. With the increase in flooding frequency, DOC/SOC and LOC/SOC increased by 80% and 26%, respectively, whereas MBC/SOC decreased by 29%. As flooding frequency increased, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) contents decreased by 81% and 35%, respectively. The decreases in POC contents were correlated with the increases in soil pH, whereas the decreases in MAOC contents were associated with the decline in clay contents. Soil carbon stability index (CSI) increased by 246% with increasing flooding frequency. These combined results indicated that SOC storage decreased, but SOC stability increased, with the increased flooding frequency. Mineral-bound organic carbon was the main protection mechanism for the SOC stability, which was of great significance to the soil C sink of the estuarine tidal wetlands.

Characterization and function analysis of a novel gene, Hc-maoc-1, in the parasitic nematode Haemonochus contortus.

BACKGROUND: Enoyl-CoA hydratase (MAOC) is required for the biosynthesis of the fatty acid-derive side chains of the ascaroside via peroxisome ß-oxidation in the free-living nematode Caenorhabditis elegans. The derivative of dideoxy-sugar, ascarylose is used as dauer pheromones or daumones to induce development of the stress-resistant dauer larvae stage. METHODS: Hc-maoc-1 gene was obtained by searching the Wellcome Trusts Sanger Institute's H. contortus genomic database. qRT-PCR was performed to analyse the transcriptional levels of Hc-maoc-1 with different developmental stages as templates. IFA was carried out to determine the expression pattern in L3 larvae and micro-injection was used to verify the promoter activity of 5'-flanking region of Hc-maoc-1. Overexpression and RNAi experiments were applied in N2 strain to ascertain the gene function of Hc-maoc-1. RESULTS: The full-length cDNA of Hc-maoc-1 was 900 bp in length, which contained eight exons separated by seven introns and possessed the Hotdog domain and the MaoC-like domain, together with several other residues and a hydratase 2 motif. It was transcribed throughout the lifecycle and peaked in the fourth-stage larvae (L4) of H. contortus; however, its transcription level decreased in diapausing L4. The protein expression and location of Hc-MAOC-1 were mainly in the intestine of L3 larvae. Overexpression of Ce-maoc-1 and Hc-maoc-1 in C. elegans showed extended lifespan and increased body size. The protein Ce-MAOC-1 and Hc-MAOC-1 were localized in the intestine with a punctate pattern. In C. elegans, knockdown of Ce-maoc-1 conferred shortened lifespan and body lengths, decreased brood size and increased lipid storage. CONCLUSION: Caenorhabditis elegans was used as a model organism to ascertain the function of Hc-maoc-1 in H. contortus. Our results showed the similar characteristics and functions with Ce-maoc-1 and provided evidences of the potential functions of Hc-maoc-1 in biosynthesis of daumones in H. contortus.