On the synthesis of the 2,6-dideoxysugar L-digitoxose

As deoxysugars are integral components of many natural products, the development of efficient chemical and enzymatic routes to prepare these compounds is of particular interest. Herein, we report a comparison of several synthetic methodologies used to prepare protected derivatives of the 2,6-dideoxysugar l-digitoxose. A novel, stereoselective synthetic route to efficiently access methyl 4-O-tert-butyldimethylsilyl-2,6-dideoxy-3-O-trimethylsilyl-alpha-l-ribo-hexopyranoside in 35% yield over nine facile steps is described.     

The role of microbicidal lipids in host defense against pathogens and their potential as therapeutic agents

Lipids such as fatty alcohols, free fatty acids and monoglycerides of fatty acids are known to be potent antimicrobial/microbicidal agents in vitro and to kill enveloped viruses, Gram-positive and Gram-negative bacteria and fungi on contact. For over half a century several studies have tried to answer the question of whether or not lipids play a role in the natural host defense against pathogens. A comprehensive review is given of these studies, particularly concerning infections in skin and in mucosal membranes of the respiratory tract, and of the role of lipids in the antimicrobial activity of breast milk. Based on studies of the microbicidal activities of lipids, both in vitro and in vivo, the possibility of using such lipids as active ingredients in prophylactic and therapeutic dosage forms is considered and examples are given of studies of such pharmaceutical dosage forms in experimental animal models and in clinical trials.     

Robustness of neural codes and its implication on natural image processing

In this study, based on the view of statistical inference, we investigate the robustness of neural codes, i.e., the sensitivity of neural responses to noise, and its implication on the construction of neural coding. We first identify the key factors that influence the sensitivity of neural responses, and find that the overlap between neural receptive fields plays a critical role. We then construct a robust coding scheme, which enforces the neural responses not only to encode external inputs well, but also to have small variability. Based on this scheme, we find that the optimal basis functions for encoding natural images resemble the receptive fields of simple cells in the striate cortex. We also apply this scheme to identify the important features in the representation of face images and Chinese characters.

庞泉沟国家自然保护区森林群落木本植物种间关系的分析

应用基于二元数据的χ²检验、方差比率法和基于数量数据的Pearson相关系数检验及Spearman秩相关系数检验等数量方法,研究了庞泉沟国家级自然保护区(东经111°22′～111°33′,北纬37°45′～37°55′）森林群落（海拔1 600～2 430 m）21个优势种的种间关系。结果表明：研究区域内森林群落优势种群的种间关系较为松散（χ²_0.95N＜W＜χ²_0.05N）,种的分布相对独立,森林群落总体处于稳定阶段;但局部地段优势种群间存在着一定程度的竞争。位于山体中下部的群丛组Ⅰ、群丛组Ⅱ的总体关联性存在一定程度的负关联,但未达到显著水平; 位于山体上部的群丛组Ⅲ的总体关联性为无关联,种间关系较为松散。随着海拔的升高,三个群丛组的联结指数(VR)呈上升趋势,χ²检验显著率和Spearman秩相关检验的正负关联比有所增加,负显著率都明显下降,正显著率有升高的趋势,说明随着海拔的升高,种间关系表现为无关联,森林群落也趋于稳定。应用方差比率法与χ2检验、Pearson相关系数检验和Spearman秩相关系数检验较为清晰地揭示了庞泉沟自然保护区森林群落的种间关系。这四种方法可以互相弥补彼此的不足,结合使用效果更好。本研究结果支持随着群落演替进程的发展,群落结构及其种类组成将逐渐趋于完善和稳定,群落种群总体种间关系也将向着无关联发展的观点。     

Variation, natural selection, and information content--a simulation

In Neo-Darwinism, variation and natural selection are the two evolutionary mechanisms that propel biological evolution. Variation implies changes in the gene pool of a population, enlarging the genetic variability from which natural selection can choose. But in the absence of natural selection, variation causes dissipation and randomization. Natural selection, in contrast, constrains this variability by decreasing the survival and fertility of the less-adapted organisms. The objective of this study is to propose a highly simplified simulation of variation and natural selection, and to relate the observed evolutionary changes in a population to its information content. The model involves an imaginary population of individuals. A quantifiable character allows the individuals to be categorized into bins. The distribution of bins (a histogram) was assumed to be Gaussian. The content of each bin was calculated after one to twelve cycles, each cycle spanning N generations (N being undefined). In a first study, selection was simulated in the absence of variation. This was modeled by assuming a differential fertility factor F that increased linearly from the lower bins (F<1.00) to the higher bins (F>1.00). The fertility factor was applied as a multiplication factor during each cycle. Several ranges of fertility were investigated. The resulting histograms became skewed to the right. In a second study, variation was simulated in the absence of selection. This was modeled by assuming that during each cycle each bin lost a fixed percentage of its content (variation factor Y) to its two adjacent bins. The resulting histograms became broader and flatter, while retaining their bilateral symmetry. Different values of Y were monitored. In a third study, various values of F and Y were combined. Our model allows the straightforward application of Shannon's equation and the calculation of a Shannon-entropy (SE) values for each histogram. Natural selection was, thus, shown to result in a progressive decrease in SE as a function of F. In other words, natural selection, when acting alone, progressively increased the information content of the population. In contrast, variation resulted in a progressive increase in SE as a function of Y. In other words, variation acting alone progressively decreased the information content of a population. When both factors, F and Y, were applied simultaneously, their relative weight determined the progressive change in SE.     

Recent advances in the structural analysis of adenylation domains in natural product biosynthesis

Adenylation (A) domains catalyze the biosynthetic incorporation of acyl building blocks into nonribosomal peptides and related natural products by selectively transferring acyl substrates onto cognate carrier proteins (CP). The use of noncanonical acyl units, such as nonproteinogenic amino acids and keto acids, by A domains expands the structural diversity of natural products. Furthermore, interrupted A domains, which have embedded auxiliary domains, are able to modify the incorporated acyl units. Structural information on A domains is important for rational protein engineering to generate unnatural compounds. In this review, we summarize recent advances in the structural analysis of A domains. First, we discuss the mechanisms by which A domains recognize noncanonical acyl units. We then focus on the interactions of A domains with CP domains and embedded auxiliary domains.     

Current capacity,bottlenecks, and future projections for offsetting habitat loss using Mitigation and Conservation banking in the United States

Habitat banking in its many iterations is an established and popular mechanism to deliver environmental offsets. The United States can look back at over 30 years of banking experience with the underlying framework and policies being consistently updated and improved. Given the increased demand in habitat banking, we provide insights into how bank area capacity is distributed across the United States for four different bank targets (wetlands, streams, multiple ecosystems, species) based on information extracted from the Regulatory In-lieu Fee and Bank Information Tracking System, as well as, estimating future capacities and area reserves through a predictive modeling approach based on data from the past 26 years. Future predictions indicate a decrease in available reserves for banks targeting wetlands or multiple ecosystems, with potential bottlenecks relating to large reserves being limited to the southeast and release schedules not catching up to the current and anticipated demand. Banks targeting species or streams are predicted to meet future demand, with species banks (conservation banks) following a different legislative and operational approach based on the listing of endangered species and pro-active approaches with anticipated future demand. Most current reserves for all four bank types are restricted to very few service areas with around one-third of all bank areas still awaiting release, limiting their availability on a broader scale. Strategic planning networks are necessary to meet future demand on a national scale and to identify areas suitable for banking or likely to experience future environmental or developmental stress.     

四川格西沟国家级自然保护区鸟类多样性初探

鸟类多样性研究是国家级自然保护区的重要工作。2020年6月—2021年5月,采用样线法和样点法,调查了四川格西沟国家级自然保护区的鸟类多样性。结果显示:结合历史文献资料,保护区共有鸟类19目56科249种。其中,国家一级重点保护动物10种,国家二级重点保护动物35种,中国特有种11种。居留型以留鸟为主,共156种(62.65%),其次是夏候鸟60种(24.10%)、旅鸟19种(7.63%)、冬候鸟14种(5.62%)。区系组成以东洋界为主,共116种(46.59%),古北界103种(41.37%)、广布种30种(12.04%)。各生态系统中森林和灌丛生态系统Shannon-Wiener指数最高,其他生态系统最低,森林和灌丛生态系统的Sorenson相似性指数最高;夏、秋季的Shannon-Wiener指数和Pielou均匀度指数最高,冬季最低。建议保护区建立长期监测体系,并持续开展鸟类保护宣传活动,加大巡护和管控力度,降低保护区内的人为干扰,同时注重鸟类所利用栖息地的保护。     

Analysis of the bacterial communities of four predatory natural enemies collected from a Northern China Bt cotton field

Predatory natural enemies are major insect species in cotton field ecosystems. Microbes that live inside these insects play essential roles in vital host activities, however, the microbiota of these insects have not been well characterized. In this study, we used Illumina 16S rRNA amplicon sequencing to investigate microbial diversity of the natural enemies Chrysoperla sinica, Harmonia axyridis, Propylaea japonica and Orius similis from a cotton field in northern China. The microbial diversity of C. sinica was low and its dominant bacterial community were Rickettsia (87.78%) and Wolbachia (6.29%). The microbial community of O. similis was more diverse than that of C. sinica. The microbial diversity of H. axyridis and P. japonica was higher, and they had similar dominant phyla, which included Firmicutes, Proteobacteria and Bacteroidetes. Their common dominant bacterial community were Romboutsia, Escherichia-Shigella, Bacteroides, Terrisporobacter, Enterobacter, Lactobacillus, Fusobacterium, Actinobacillus, Sphaerochaeta, Bacteroidales_S24-7_group and Cyanobacteria. This study also forms the basis for further study on the microbiota of natural enemies from different habitats.     

Translating chemometric analysis into physiological insights from in vivo confocal Raman spectroscopy of the human stratum corneum

The superficial layer of the skin, the stratum corneum (SC), consists of corneocytes surrounded by lipid regions and acts as a protective barrier for the body against water loss, toxic agents and microorganisms. As most substances permeate the stratum corneum through the lipid regions, lipid organization is considered crucial for the skin barrier function. Here, we investigate the potential of in vivo confocal Raman spectroscopy to describe the composition and organization of the SC. Confocal Raman spectroscopy is finding increasing use in the characterization of skin in biomedical, pharmaceutical and cosmetic applications. In this work, we analyze the spectra using chemometric methods and obtain principal components that correspond to the primary skin constituents: protein (keratin), natural moisturizing factor (NMF), water and lipid contributions in both ordered (orthorhombic) and disordered structural organization. By identifying these important components of the SC, these results highlight the utility of this in vivo, non-invasive, and depth resolved tool at the forefront of skin research.