AvaR1, a Butenolide-Type Autoregulator Receptor in Streptomyces avermitilis, Directly Represses Avenolide and Avermectin Biosynthesis and Multiple Physiological Responses

Avermectins are commercially important anthelmintic antibiotics produced by Streptomyces avermitilis. The homologous TetR-family transcriptional regulators AvaR1 and AvaR2 in this species were identified previously as receptors of avenolide, a novel butenolide-type autoregulator signal required for triggering avermectin biosynthesis. AvaR2 was found to be an important pleiotropic regulator in repression of avermectin and avenolide production and cell growth, whereas the regulatory role of AvaR1 remains unclear. Investigation of AvaR1 function in the present study showed that it had no effect on cell growth or morphological differentiation, but inhibited avenolide and avermectin production mainly through direct repression of aco (the key enzyme gene for avenolide biosynthesis) and aveR (the cluster-situated activator gene). AvaR1 also directly repressed its own gene (avaR1) and two adjacent homologous genes (avaR2 and avaR3). Binding sites of AvaR1 on these five target promoter regions completely overlapped those of AvaR2, leading to the same consensus binding motif. However, AvaR1 and AvaR2 had both common and exclusive target genes, indicating that they cross-regulate diverse physiological processes. Ten novel identified AvaR1 targets are involved in primary metabolism, stress responses, ribosomal protein synthesis, and cyclic nucleotide degration, reflecting a pleiotropic role of AvaR1. Competitive EMSAs and GST pull-down assays showed that AvaR1 and AvaR2 competed for the same binding regions, and could form a heterodimer and homodimers, suggesting that AvaR1 and AvaR2 compete and cooperate to regulate their common target genes. These findings provide a more comprehensive picture of the cellular responses mediated by AvaR1 and AvaR2 regulatory networks in S. avermitilis

Transcriptional Regulator DasR Represses Daptomycin Production through Both Direct and Cascade Mechanisms in <i>Streptomyces roseosporus</i>

Daptomycin, produced by Streptomyces roseosporus, is a clinically important cyclic lipopeptide antibiotic used for the treatment of human infections caused by drug-resistant Gram-positive pathogens. In contrast to most Streptomyces antibiotic biosynthetic gene clusters (BGCs), daptomycin BGC has no cluster-situated regulator (CSR) genes. DasR, a GntR-family transcriptional regulator (TR) widely present in the genus, was shown to regulate antibiotic production in model species S. coelicolor by binding to promoter regions of CSR genes. New findings reported here reveal that DasR pleiotropically regulates production of daptomycin and reddish pigment, and morphological development in S. roseosporus. dasR deletion enhanced daptomycin production and morphological development, but reduced pigment production. DasR inhibited daptomycin production by directly repressing dpt structural genes and global regulatory gene adpA (whose product AdpA protein activates daptomycin production and morphological development). DasR-protected regions on dptEp and adpAp contained a 16 nt sequence similar to the consensus DasR-binding site dre in S. coelicolor. AdpA was shown to target dpt structural genes and dptR2 (which encodes a DeoR-family TR required for daptomycin production). A 10 nt sequence similar to the consensus AdpA-binding site was found on target promoter regions dptAp and dptR2p. This is the first demonstration that DasR regulates antibiotic production both directly and through a cascade mechanism. The findings expand our limited knowledge of the regulatory network underlying daptomycin production, and will facilitate methods for construction of daptomycin overproducers

An on-demand scheme driven by the knowledge of geospatial distribution for large-scale high-resolution impervious surface mapping

Impervious surface has become one of the key factors of regional environmental problems and disasters. There rises an urgent need for mapping large-scale high-resolution impervious surfaces to help delicate modeling and overall planning. In the existing large-scale impervious surface mapping studies, there are many studies and products at medium resolution (10 ~ 100 m), some of which are with time series; while only few are at high resolution (<10 m), but not appeared with temporal updates. In the conventional scheme for large-scale high-resolution mapping, plenty of high-resolution imagery (HRI) are required to cover the entire large area and achieve wider coverage as much as possible. The high cost of obtaining abundant HRI limits large-scale high-resolution impervious surface mapping, leading to rare high-resolution impervious surface study at large scales. To alleviate the difficulties in the conventional scheme, an on-demand HRI scheme was proposed based on geos`patial distribution knowledge (low overall proportion and high geospatial aggregation) of impervious surface at large scales, with the advantage of reducing the demand for HRI while ensuring coverage. Adopting the information and knowledge obtained from medium-resolution impervious surface data at large scales, the proposed on-demand HRI scheme only requires HRI where it is really needed, rather than for the entire large area as in the conventional scheme. Reducing the study area by a morphology-based method and selecting necessary HRI by the bidirectional image filtering (BIF) strategy, the on-demand HRI scheme has a smaller requirement of the HRI resources. The proposed on-demand HRI scheme and conventional scheme were implemented and discussed in five study areas. The results show that compared with the conventional method, the proposed on-demand HRI scheme reduced the requirement of HRI while ensuring coverage; and in the case of insufficient HRI coverage, it can reduce the HRI requirements while narrowing data gaps in the large-scale high-resolution impervious surface result. It was also found that the proposed scheme performs well in large-scale areas with low overall proportion and high geospatial aggregation of impervious surface found in the medium-resolution remote sensing product. Additionally, the on-demand HRI scheme will be also useful for large-scale high-resolution mapping of other land cover types

6Ds-HLM: Hierarchical models of road traffic crash influencing factor analysis considering the urban built environment of intersection visibility

Road traffic safety issues pose a serious threat to urban health, and how the built environment affects traffic crashes has been hotly discussed. However, there are limitations in the selection of built environment factors according to the classic 5Ds system in most previous studies. Few studies have considered the influence exerted by visibility factors in intersection level and road diversity at the community level on traffic crashes, and the multi-level structure of crash data may be ignored. Therefore, the proposed visibility analysis method considering visible triangles and visual sensitivity is used to quantify the visual environment features of the intersections. Based on the proposed six-dimensional factors (6Ds) of the built environment (considering the intersection visibility degree and road diversity) and the hierarchical linear model (HLM), this paper proposes the 6Ds-HLM framework to analyze how road traffic crashes are influenced by the built environment factors. The results show that (1) the full model of the proposed 6Ds-HLM which contained the variables of intersection level and community level considering road diversity and the cross-level interactive effect performed best. (2) Interactive effects between intersection visibility and community built environment are founded, and significant 6Ds variables are identified using HLM: a) There was a positive cross-effect between intervisibility and road diversity. The viewshed area of the middle visual sensitive region also presented significant positive cross effects with traffic congestion speed, entertainment venue density, and road diversity. b) There was a significant negative cross-effect between the viewshed area of the middle visual sensitive region and school density

Experimental Verification of Reservoirs with Different Wettability Using an Oil&ndash;Water Relative Permeability Model

Oil&ndash;water relative permeability is an important parameter that affects fluid flow in porous media. It is usually obtained in a laboratory. Since rock resistivity and relative permeability are both effects of water saturation, they should theoretically have a relationship. Based on the parallel conduction principle of fluid and skeleton in porous media, the pore structure and fluid distribution can be simplified using the Kozeny&ndash;Carman permeability correction equation and the Archie formula, and the relative permeability model of the water phase can be deduced under different wetting conditions. In this study, the resistivity and relative permeability experimental data of 20 rock samples from four inspection wells were compared and verified. The results show that the proposed oil&ndash;water relative permeability model agrees well with a reservoir having a porosity range of 17.6&ndash;30.7% and an air permeability of 0.16&ndash;973 &times; 10&minus;3 &mu;m, and it may explain why the relative permeability of the water phase decreases as water saturation increases. This model could provide a new technique to construct the relative permeability curves of sandstone reservoirs

High-Pressure Solidification of Ternary Al-Ni-Sn Alloy

The microstructure, phase composition and mechanical properties of ternary Al-5.4Ni-2Sn (mass fraction) alloy solidified under different high pressures were researched. The results show that the phase composition of the alloy solidified at different pressures is Al, Al3Ni and β-Sn. The thermodynamic phase diagram of the ternary alloy Al-5.4Ni-2Sn was calculated under the equilibrium condition. The results demonstrate that the solidification process is as follows: L→Al3Ni→(α-Al + Al3Ni)eutectic→(α-Al + Al3Ni + β-Sn)eutectic. The hardness values of α-Al phase at ambient pressure, 2 GPa and 4 GPa are 1.5 GPa, 1.62 GPa and 1.99 GPa, respectively. This is an increase of 8% and 32.7%, respectively. The hardness of β-Sn phase decreases by about 31.2% at 4 GPa. When the deformation is 30%, the compressive strength at ambient pressure, 2 GPa and 4 GPa is 538.1 MPa, 1403.2 MPa and 1547.9 MPa, respectively. The compressive strength under high pressure increased by 160.85% and 187.7%, respectively

High-Pressure Solidification of Ternary Al-Ni-Sn Alloy

The microstructure, phase composition and mechanical properties of ternary Al-5.4Ni-2Sn (mass fraction) alloy solidified under different high pressures were researched. The results show that the phase composition of the alloy solidified at different pressures is Al, Al3Ni and &beta;-Sn. The thermodynamic phase diagram of the ternary alloy Al-5.4Ni-2Sn was calculated under the equilibrium condition. The results demonstrate that the solidification process is as follows: L&rarr;Al3Ni&rarr;(&alpha;-Al + Al3Ni)eutectic&rarr;(&alpha;-Al + Al3Ni + &beta;-Sn)eutectic. The hardness values of &alpha;-Al phase at ambient pressure, 2 GPa and 4 GPa are 1.5 GPa, 1.62 GPa and 1.99 GPa, respectively. This is an increase of 8% and 32.7%, respectively. The hardness of &beta;-Sn phase decreases by about 31.2% at 4 GPa. When the deformation is 30%, the compressive strength at ambient pressure, 2 GPa and 4 GPa is 538.1 MPa, 1403.2 MPa and 1547.9 MPa, respectively. The compressive strength under high pressure increased by 160.85% and 187.7%, respectively