Single Cell Analysis Linking Ribosomal (r)DNA and rRNA Copy Numbers to Cell Size and Growth Rate Provides Insights into Molecular Protistan Ecology

Ribosomal (r)RNA and rDNA have been golden molecular markers in microbial ecology. However, it remains poorly understood how ribotype copy number (CN)‐based characteristics are linked with diversity, abundance, and activity of protist populations and communities observed at organismal levels. Here, we applied a single‐cell approach to quantify ribotype CNs in two ciliate species reared at different temperatures. We found that in actively growing cells, the per‐cell rDNA and rRNA CNs scaled with cell volume (CV) to 0.44 and 0.58 powers, respectively. The modeled rDNA and rRNA concentrations thus appear to be much higher in smaller than in larger cells. The observed rRNA:rDNA ratio scaled with CV^0.14. The maximum growth rate could be well predicted by a combination of per‐cell ribotype CN and temperature. Our empirical data and modeling on single‐cell ribotype scaling are in agreement with both the metabolic theory of ecology and the growth rate hypothesis, providing a quantitative framework for linking cellular rDNA and rRNA CNs with body size, growth (activity), and biomass stoichiometry. This study also demonstrates that the expression rate of rRNA genes is constrained by cell size, and favors biomass rather than abundance‐based interpretation of quantitative ribotype data in population and community ecology of protists.     

Rhodobacteraceae on the marine brown alga Fucus spiralis are abundant and show physiological adaptation to an epiphytic lifestyle

Macroalgae harbour specific microbial communities on their surface that have functions related to host health and defence. In this study, the bacterial biofilm of the marine brown alga Fucus spiralis was investigated using 16S rRNA gene amplicon-based analysis and isolation of bacteria. Rhodobacteraceae (Alphaproteobacteria) were the predominant family constituting 23% of the epibacterial community. At the genus level, Sulfitobacter, Loktanella, Octadecabacter and a previously undescribed cluster were most abundant, and together they comprised 89% of the Rhodobacteraceae. Supported by a specific PCR approach, 23 different Rhodobacteraceae-affiliated strains were isolated from the surface of F. spiralis, which belonged to 12 established and three new genera. For seven strains, closely related sequences were detected in the 16S rRNA gene dataset. Growth experiments with substrates known to be produced by Fucus spp. showed that all of them were consumed by at least three strains, and vitamin B₁₂ was produced by 70% of the isolates. Since growth of F. spiralis depends on B₁₂ supplementation, bacteria may provide the alga with this vitamin. Most strains produced siderophores, which can enhance algal growth under iron-deficient conditions. Inhibiting properties against other bacteria were only observed when F. spiralis material was present in the medium. Thus, the physiological properties of the isolates indicated adaption to an epiphytic lifestyle.     

遥感反演植被含氮量研究进展

植被含氮量表征植被氮素状态。它作为植被生长状况的重要指标,在生态系统健康状况检测、生态系统生产估测、精准农业、生态系统干扰评估等方面均有重要意义。遥感监测植被含氮量主要基于高光谱和多光谱数据,采用的算法包括经验方法(波谱指数与回归分析)及物理方法(辐射传输模型法)。但受数据源和研究方法的局限,目前植被氮含量遥感监测局限于区域范围较小且内部植被类型与环境条件(气候、地形等)基本一致的情形,而对复杂生态系统的监测能力不足。未来的研究需针对氮沉降和人类活动的生态系统响应这一重大研究需求,发展和改进现有植被含氮量遥感反演方法。可考虑开展对不同环境条件下、不同类型植被光谱曲线进行标准化的研究,以形成普适的植被含氮量反演方法。并考虑综合运用多种数据(如微波遥感、无人机遥感),形成多尺度同步监测,以提高遥感对区域乃至全球范围内植被氮含量常规监测的能力。     

Leaf phenology mediates provenance differences in herbivore populations on valley oaks in a common garden

1. Plants from different populations often display a variation in herbivore resistance. However, it is rarely understood what plant traits mediate such differences. 2. It was tested how leaf phenology affects herbivore populations in a 15‐year‐old common garden of valley oaks (Quercus lobata Née) with different populations and maternal parents from throughout the Q. lobata range. 3. The abundance of leaf miners (Stigmella sp. Shrank) and leaf phenology of oaks in the common garden was measured. 4. Leaf miner abundance varied among provenance locations (population), but not among maternal parents within populations. Leaf phenology varied by provenance location and maternal parent, and trees that leafed out earlier accrued higher leaf‐miner abundance. Path analysis indicated that leaf phenology was the likely driver of provenance and parental differences in resistance to leaf miners. 5. Understanding population differences is particularly important when considering transport of genotypes for ornamental or restoration purposes. The present study suggests that similarity in leaf phenology may be one factor that could be used to find genotypes with a similar herbivore resistance to local genotypes.     

Isolation,Culture and Long-Term Maintenance of Primary Mesencephalic Dopaminergic Neurons From Embryonic Rodent Brains

Degeneration of mesencephalic dopaminergic (mesDA) neurons is the pathological hallmark of Parkinson’s diseae. Study of the biological processes involved in physiological functions and vulnerability and death of these neurons is imparative to understanding the underlying causes and unraveling the cure for this common neurodegenerative disorder. Primary cultures of mesDA neurons provide a tool for investigation of the molecular, biochemical and electrophysiological properties, in order to understand the development, long-term survival and degeneration of these neurons during the course of disease. Here we present a detailed method for the isolation, culturing and maintenance of midbrain dopaminergic neurons from E12.5 mouse (or E14.5 rat) embryos. Optimized cell culture conditions in this protocol result in presence of axonal and dendritic projections, synaptic connections and other neuronal morphological properties, which make the cultures suitable for study of the physiological, cell biological and molecular characteristics of this neuronal population.