Impacts of florfenicol on the microbiota landscape and resistome as revealed by metagenomic analysis.

BACKGROUND:Drug-resistant fish pathogens can cause significant economic loss to fish farmers. Since 2012, florfenicol has become an approved drug for treating both septicemia and columnaris diseases in freshwater fish. Due to the limited drug options available for aquaculture, the impact of the therapeutical florfenicol treatment on the microbiota landscape as well as the resistome present in the aquaculture farm environment needs to be evaluated. RESULTS:Time-series metagenomic analyses were conducted to the aquatic microbiota present in the tank-based catfish production systems, in which catfish received standard therapeutic 10-day florfenicol treatment following the federal veterinary regulations. Results showed that the florfenicol treatment shifted the structure of the microbiota and reduced the biodiversity of it by acting as a strong stressor. Planctomycetes, Chloroflexi, and 13 other phyla were susceptible to the florfenicol treatment and their abundance was inhibited by the treatment. In contrast, the abundance of several bacteria belonging to the Proteobacteria, Bacteroidetes, Actinobacteria, and Verrucomicrobia phyla increased. These bacteria with increased abundance either harbor florfenicol-resistant genes (FRGs) or had beneficial mutations. The florfenicol treatment promoted the proliferation of florfenicol-resistant genes. The copy number of phenicol-specific resistance genes as well as multiple classes of antibiotic-resistant genes (ARGs) exhibited strong correlations across different genetic exchange communities (p < 0.05), indicating the horizontal transfer of florfenicol-resistant genes among these bacterial species or genera. Florfenicol treatment also induced mutation-driven resistance. Significant changes in single-nucleotide polymorphism (SNP) allele frequencies were observed in membrane transporters, genes involved in recombination, and in genes with primary functions of a resistance phenotype. CONCLUSIONS:The therapeutical level of florfenicol treatment significantly altered the microbiome and resistome present in catfish tanks. Both intra-population and inter-population horizontal ARG transfer was observed, with the intra-population transfer being more common. The oxazolidinone/phenicol-resistant gene optrA was the most prevalent transferred ARG. In addition to horizontal gene transfer, bacteria could also acquire florfenicol resistance by regulating the innate efflux systems via mutations. The observations made by this study are of great importance for guiding the strategic use of florfenicol, thus preventing the formation, persistence, and spreading of florfenicol-resistant bacteria and resistance genes in aquaculture

Thermomechanical analysis of rock asperity in fractures of enhanced geothermal systems

Enhanced Geothermal Systems (EGS) offer great potential for dramatically expanding the use of geothermal energy and become a promising supplement for fossil energy. The EGS is to extract heat by creating a subsurface system to which cold water can be added through injection wells. Injected water is heated by contact with rock and returns to the surface through production well. Fracture provides the primary conduit for fluid flow and heat transfer in natural rock. Fracture is propped by fracture roughness with varying heights which is called asperity. The stability of asperity determines fracture aperture and hence imposes substantial effect on hydraulic conductivity and heat transfer efficiency in EGS. Firstly, two rough fracture surfaces are characterized by statistical method and fractal analysis. The asperity heights and enclosed aperture heights are described by probability density function before cold water is pumped into fracture. Secondly, when water injection and induced cooling occurs, the thermomechanical analysis of single asperity is studied by establishing an un-symmetric damage mechanics model. The deformation curve of asperity under thermal stress is determined. Thirdly, deformation of fracture with various asperities on it in response to thermal stress is analyzed by a new stratified continuum percolation model. This model incorporates the fracture surface characteristics and preceding deformation curve of asperity. The fracture closure and fracture stiffness can be accurately quantified by this model. In addition, the scaling invariance and multifractal parameters in this process are identified and validated with Monte Carlo simulation --Abstract, page iii

Rank properties and computational methods for orthogonal tensor decompositions

The orthogonal decomposition factorizes a tensor into a sum of an orthogonal list of rankone tensors. We present several properties of orthogonal rank. We find that a subtensor may have a larger orthogonal rank than the whole tensor and prove the lower semicontinuity of orthogonal rank. The lower semicontinuity guarantees the existence of low orthogonal rank approximation. To fit the orthogonal decomposition, we propose an algorithm based on the augmented Lagrangian method and guarantee the orthogonality by a novel orthogonalization procedure. Numerical experiments show that the proposed method has a great advantage over the existing methods for strongly orthogonal decompositions in terms of the approximation error.Comment: 19 pages, 2 figures, 3 table

The contracts between leading agribusiness enterprises and rural households: its effects on firm-level export of agricultural products

In this paper, transaction cost is introduced into the general firm-level export behavior model. By so doing, we build a theoretical model explaining how connection modes between leading agribusiness enterprises and rural households affect the firm-level agricultural products export. Analyzing the dataset of 561 national leading agribusinesses of the year 2003, we use Tobit model to estimate the firm-level export effect of the connection modes. The empirical result demonstrates that connections in the mode of stock-cooperation or cooperation contracts have a significant positive effect on the enterprises export and export ratio. In addition, the connection with more characteristics of factor contract has stronger effect on export than that with commodity contract characteristics.Contracts; Agribusiness; Rural Households; Firm-level; Export