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Antimicrobial Spirotetronate Metabolites from Marine-Derived Micromonospora harpali SCSIO GJ089
No full textTwo new spirotetronate aglycones, 22-dehydroxymethyl-kijanolide (1) and 8-hydroxy-22-dehydroxymethyl-kijanolide (2), along with seven new spirotetronate glycosides, microsporanates A-F (3-8) and tetrocarcin P (9), together with three known tetrocarcins [tetrocarcins A (10), B (11), and AC6H (12)], were isolated from fermentation broths of the marine-derived Micromonospora harpali SCSIO GJ089. The structures of 1-9 were elucidated on the basis of 1D and 2D NMR and MS spectroscopic data. Compounds 3-8 feature an alpha,beta-unsaturated carbonyl moiety within their spirotetronate skeletons. Moreover, compounds 3-12 displayed strong to moderate antibacterial activities against Gram with MIC values ranging from 0.016 to 8.0 mu g/mL
Identification of nocamycin biosynthetic gene cluster from Saccharothrix syringae NRRL B-16468 and generation of new nocamycin derivatives by manipulating gene cluster
No full textBackground: Nocamycins I and II, produced by the rare actinomycete Saccharothrix syringae, belong to the tetramic acid family natural products. Nocamycins show potent antimicrobial activity and they hold great potential for antibacterial agent design. However, up to now, little is known about the exact biosynthetic mechanism of nocamycin. Results: In this report, we identified the gene cluster responsible for nocamycin biosynthesis from S. syringae and generated new nocamycin derivatives by manipulating its gene cluster. The biosynthetic gene cluster for nocamycin contains a 61 kb DNA locus, consisting of 21 open reading frames (ORFs). Five type I polyketide synthases (NcmAI, NcmAII, NcmAIII, NcmAIV, NcmAV) and a non-ribosomal peptide synthetase (NcmB) are proposed to be involved in synthesis of the backbone structure, a Dieckmann cyclase NcmC catalyze the releasing of linear chain and the formation of tetramic acid moiety, five enzymes (NcmEDGOP) are related to post-tailoring steps, and five enzymes (NcmNJKIM) function as regulators. Targeted inactivation of ncmB led to nocamycin production being completely abolished, which demonstrates that this gene cluster is involved in nocamycin biosynthesis. To generate new nocamycin derivatives, the gene ncmG, encoding for a cytochrome P450 oxidase, was inactivated. Two new nocamycin derivatives nocamycin III and nocamycin IV were isolated from the ncmG deletion mutant strain and their structures were elucidated by spectroscopic data analyses. Based on bioinformatics analysis and new derivatives isolated from gene inactivation mutant strains, a biosynthetic pathway of nocamycins was proposed. Conclusion: These findings provide the basis for further understanding of nocamycin biosynthetic mechanism, and set the stage to rationally engineer new nocamycin derivatives via combinatorial biosynthesis strategy
Interannual to decadal variation of spring sea level anomaly in the western South China Sea
No full textSatellite observations of sea level anomalies (SLA) from January 1993 to December 2012 are used to investigate the interannual to decadal changes of the boreal spring high SLA in the western South China Sea (SCS) using the Empirical Orthogonal Function (EOF) method. We find that the SLA variability has two dominant modes. The Sea Level Changing Mode (SLCM) occurs mainly during La Nia years, with high SLA extension from west of Luzon to the eastern coast of Vietnam along the central basin of the SCS, and is likely induced by the increment of the ocean heat content. The Anticyclonic Eddy Mode (AEM) occurs mainly during El Nio years and appears to be triggered by the negative wind curl anomalies within the central SCS. In addition, the spring high SLA in the western SCS experienced a quasi-decadal change during 1993-2012; in other words, the AEM predominated during 1993-1998 and 2002-2005, while the La Nia-related SLCM prevailed during 1999-2001 and 2006-2012. Moreover, we suggest that the accelerated sea level rise in the SCS during 2005-2012 makes the SLCM the leading mode over the past two decades
Spatial assessment of water quality using chemometrics in the Pearl River Estuary, China
No full textA cruise was commissioned in the summer of 2009 to evaluate water quality in the Pearl River Estuary (PRE). Chemometrics such as Principal Component Analysis (PCA), Cluster analysis (CA) and Self-Organizing Map (SOM) were employed to identify anthropogenic and natural influences on estuary water quality. The scores of stations in the surface layer in the first principal component (PC1) were related to NH4-N, PO4-P, NO2-N, NO3-N, TP, and Chlorophyll a while salinity, turbidity, and SiO3-Si in the second principal component (PC2). Similarly, the scores of stations in the bottom layers in PC1 were related to PO4-P, NO2-N, NO3-N, and TP, while salinity, Chlorophyll a, NH4-N, and SiO3-Si in PC2. Results of the PCA identified the spatial distribution of the surface and bottom water quality, namely the Guangzhou urban reach, Middle reach, and Lower reach of the estuary. Both cluster analysis and PCA produced the similar results. Self-organizing map delineated the Guangzhou urban reach of the Pearl River that was mainly influenced by human activities. The middle and lower reaches of the PRE were mainly influenced by the waters in the South China Sea. The information extracted by PCA, CA, and SOM would be very useful to regional agencies in developing a strategy to carry out scientific plans for resource use based on marine system functions
Ship observations and numerical simulation of the marine atmospheric boundary layer over the spring oceanic front in the northwestern South China Sea
No full textThe response of the marine atmospheric boundary layer (MABL) structure to an oceanic front is analyzed using Global Positioning System (GPS) sounding data obtained during a survey in the northwestern South China Sea (NSCS) over a period of about 1week in April 2013. The Weather Research and Forecasting (WRF) model is used to further examine the thermodynamical mechanisms of the MABL's response to the front. The WRF model successfully simulates the change in the MABL structure across the front, which agrees well with the observations. The spatially high-pass-filtered fields of sea surface temperature (SST) and 10m neutral equivalent wind from the WRF model simulation show a tight, positive coupling between the SST and surface winds near the front. Meanwhile, the SST front works as a damping zone to reduce the enhancement of wind blowing from the warm to the cold side of the front in the lower boundary layer. Analysis of the momentum budget shows that the most active and significant term affecting horizontal momentum over the frontal zone is the adjustment of the pressure gradient. It is found that the front in the NSCS is wide enough for slowly moving air parcels to be affected by the change in underlying SST. The different thermal structure upwind and downwind of the front causes a baroclinic adjustment of the perturbation pressure from the surface to the midlayer of the MABL, which dominates the change in the wind profile across the front
Using zircon U-Pb ages to constrain the provenance and transport of heavy minerals within the northwestern shelf of the South China Sea
No full textNumerous ore-grade heavy mineral placer deposits occur in the northern South China Sea region. Previous studies on these deposits have focused on the heavy-mineral ore resources themselves, but the provenance and transport pathways of these heavy minerals are poorly constrained. This paper presents U-Pb ages of detrital zircons from sediments within the northwestern shelf of the South China Sea, and uses this new dataset to determine the provenance and transport pathway of the sediments. Zircons in sediments from ten areas of the northwestern shelf exhibit distinct age populations, suggesting that they have multiple provenances. Zircons in sediments from the Pearl River Mouth, Shangchuan Island, and Moyang River Mouth areas all have an obvious peak of Mesozoic ages, indicating that they have similar sediment provenances; i.e., mainly from the Pearl River, and to a lesser degree from the Moyang River. Zircons in sediments from the areas around the Jian River Mouth and Leizhou Bay, and off Hainan Island have an early Paleozoic age, suggesting that the sediments predominantly originate from the Yunkai massif. Zircons of the sediments from the remaining four areas, the Leigiong Strait, Wanquan River Mouth, Qiongdongnan, and the Outer Shelf, have Yanshannian and Indosinian age peaks in addition to an obvious early Paleozoic population, implying mixed provenances, including the Yunkai massif and Hainan Island. The sediment transport may have involved two hydrodynamic conditions in two distinct stages. First, the Guangdong Longshore Current carried the river sediments to where they dispersed in the inner shelf; subsequently, wave-induced strong currents further transported sandy sediments southeastward to the outer shelf. In addition to explaining the provenance and transport pathways of heavy minerals within the northwestern shelf of the South China Sea, these results provide new information relevant to exploration for heavy-mineral placer deposits. (C) 2016 Published by Elsevier Ltd
Tectonics of the Indo-Australian plate near the Ninetyeast Ridge constrained from marine gravity and magnetic data
No full textAlthough the Indo-Australian plate near the Ninetyeast Ridge is important for understanding the formation of new plate boundaries, its tectonic problems are complex and most of them are poorly known. This paper made a detailed tectonic analysis based on the data of bathymetry, gravity and magnetics. Bathymetry and gravity maps show morphological features of many folds, which are related to the intraplate deformation of the Indo-Australian plate due to the collision between the Indian and Asian plates. Gravity anomalies show the structure of fracture zones, which are caused by the seafloor spreading and transform faulting. The characteristics of the folds and fracture zones are consistent with the hypothesis that diffuse plate boundaries and redefined plate components would occur within the Indo-Australian plate. In addition, compiled magnetic data demonstrate magnetic lineations, abandoned spreading centers, southward ridge jumps and plate motions. These features provide useful information for rebuilding the tectonic evolution history of the study area. Magnetic anomalies suggest that an additional plate boundary of transform fault type is developing
Composition and genesis of ferromanganese deposits from the northern South China Sea
No full textMarine ferromanganese (Fe-Mn) nodules and crusts are archives of past environmental conditions and potential mineral resources. Over the last 30 years, many have been discovered in the northern South China Sea (SCS). To determine the origin of the Fe-Mn deposits, a comprehensive laboratory analysis of physical properties, mineralogy and geochemistry was conducted on newly collected Fe-Mn nodule/crust samples. The results revealed that there are three types of Fe-Mn deposits: (1) Fe-rich nodules containing essentially goethite occur on the northeastern slope of the SCS, with high Fe, low Mn (Mn/Fe = 0.03) and low trace metals and rare earth elements concentrations; (2) Smooth Fe-Mn nodules and crusts composed of asbolane, todorokite and CFA occur along the northwestern marginal of the SCS that have similar Fe and Mn contents (Mn/Fe = 1.21), moderate trace metal enrichments, and a positive Ce anomaly; (3) Fe-Mn nodules and crusts composed of asbolane, todorokite and birnessite that occur in the central basin of the SCS have higher Mn and lower Fe contents (Mn/Fe = 1.45). This depositional pattern was associated with major changes in oceanographic conditions and tectonic regimes. The northeastern slope deposits occur in a contourite depositional system, are strongly enriched in Fe relative to Mn (average 38.7% and 0.96%, respectively), formed from the combination of hydrogenetic and diagenetic processes. We propose a new genetic model for Fe-Mn nodules, which formed through the oxidation of pyrite and pyrite-barite concretions that formed by rapid early diagenetic growth (average 3320 mm/Myr) on continental margins above the carbonate compensation depth, and dominated by hydrocarbon seep structures and strong erosive action of bottom currents along the northeastern slope. In contrast, the introduction of vigorous deep-water flow from the North Pacific promoted the slow growth (4-7 mm/Myr) of hydrogenetic Fe-Mn nodules and crusts along the northwestern margin. Finally, hydrogenetic growth of Fe-Mn nodules and crusts in the central basin may have been enhanced by volcanic processes. Our data provide new insights into the genesis and province characteristics of the Fe-Mn nodules and crusts of the northern SCS. (C) 2017 Elsevier Ltd. All rights reserved
Deep structure imaging of multi-geophysical parameters and seismogenesis in the Longmenshan fault zone
No full textDeep structures of seismic velocity and Poisson's ratio are imaged along the Longmenshan fault zone using a large number of arrival-time data of P- and S-waves. Together with magnetotelluric (MT) data analyzing, we consider that the crustal deformation is closely related to the deep seismic velocity, Poisson's ratio and conductivity structural heterogeneities. The generations of the 2008 Wenchuan and 2013 Lushan earthquakes are associated with the crustal deformation process and fluid intrusion from the lower crust of Tibet into the seismogenic layer along the fault zone. Our results indicate that the 2008 Wenchuan and 2013 Lushan earthquakes are located in the high velocity and high resistivity zones within the seismogenic layer. Anomalously slow velocity with low resistivity in the Sichuan foreland basin is in sharp contrast to high-velocity and high-resistivity anomalies in the upper crust in the Songpan-Garze block. This contrasting feature of the anomalies could reflect the Mesozoic and Paleozoic sediments with thickness variation of several kilometers to more than 10 kilometers in the Sichuan Basin. The tomographic model presented here reveals two crustal bodies with anomalously slow velocity and high conductivity underneath the Longmenshan fault zone which is separated into three contrasting segments by the two bodies. We interpreted these low-velocity and low-resistivity bodies as being associated with extrusion of either fluids or products of partial melting from the lower crust, the upper mantle, or both in the Songpan-Garze block, which suggests strong variations in the rheological strength of the rock along the fault zone. This finding implies that the coupling between these presumably fluid-bearing bodies and earthquake generation could be extremely complex and that there is dramatic variation from the southwestern portion to the northeastern segment along the fault belt. We then conclude that the 2008 Wenchuan earthquake generation as well as its rupture process is controlled by the structural heterogeneities together with the fluids intruding from the lower crust of the central plateau. The 2013 Lushan earthquake might have been triggered by the high pore-pressure accumulated in source area from both the lower crustal fluids intrusion and the stress transmission of the 2008 Wenchuan earthquake in the seismogenic layer. Our study suggests that the rheological variation in the crust and fluids bearing stress accumulation along the Longmenshan fault zone played a principal role in controlling seismic generation and rupture processes during the 2008 Wenchuan and 2013 Lushan earthquakes
Precambrian continental crust evolution of Hainan Island in South China: Constraints froM detrital zircon Hf isotopes of metaclastic-sedimentary rocks in the Shilu Fe-Co-Cu ore district
No full textCombined with the previous detrital zircons U-Pb ages of the two Precambrian successions, i.e. the Shilu Group and the Shihuiding Formation in Hainan Island of South China, the in situ Lu-Hf isotopes of detrital zircons were performed to evaluate the growth and reworking of Hainan Island continental crust during Precambrian. The results of 171 Hf-isotopic analyses on zircon grains from the Shihuiding Formation yield Hf-176/Hf-177 ratios between 0.280786 and 0.281188, Lu-176/Hf-177 ratios between 0.000228 and 0.003388, Hf model ages (T-DM(C)) between 3.8 Ga and 1.2 Ga, and epsilon(Hf)(t) values ranging from -12.5 to +10.6. The analyzed results of 272 Hf-isotopic data on zircon grains from the Shilu Group exhibit a wide range of Hf-176/Hf-177 ratios (0.280810-0.282512), Lu-176/Hf-177 ratios (0.000062-0.004060), T-DM(C) ages (3.7 Ga-1.1 Ga), and epsilon(Hf)(t) values (-20.5 to +12.3). The continental crust of Hainan Island maybe appeared firstly at ca. 4.0-3.8 Ga and then was reworked. The 91.8% of detrital zircon grains from the Shihuiding Formation and 93.8% of the ones from the Shilu Group have crustal incubation time larger than 300 Ma, indicating an involvement of reworked materials into the sedimentation of both the successions. Unambiguously, the crustal basement rocks in Hainan Island were formed mainly through reworking the previous continental components with minor input of juvenile materials. The generation of juvenile curst in Hainan Island predominantly occurred at ca. 2.7 Ga and ca. 1.5-1.0 Ga, which are consistent with that for the assembly of the Kenorland, and the Columbia breakup and subsequent amalgamation of the Rodinia, respectively. The present study further reveals that the crustal growths in Hainan Island are present at 2.7 Ga, 2.3 Ga and 2.1-1.8 Ga, which is more favorable to the episodic growth mode. Moreover, a rough trend of decreasing maximum crustal incubation time of Hainan Island demonstrates that the incubation time of the juvenile crust is shorter when compared with that of the Cathaysia Block in the late Mesoproterozoic. Link to the previously reported geological works, we consider that Hainan Island did not share the same evolution history with the Cathaysia Block of South China during Precambrian. (C) 2017 Elsevier B.V. All rights reserved