Nucleoid Visible vs. Non-Nucleoid Visible Bacterial Cells: A New Approach to Assessing in Situ Bacterioplankton Dynamics

异养细菌处理了海洋中很大一部分初级产品，并负责海洋食物网中很大一部分的呼吸和再矿化。因此，阐明细菌的作用对于了解海洋生态系统的结构和功能，特别是海洋生物群在隔绝大气二氧化碳方面的作用至关重要。一种新的表观荧光DNA染色方法表明，浮游细菌可以分为两组细胞：有可见类核的细胞和没有可见类核的细胞（通过该方法可见）。初步研究表明，具有可见类核的细胞（NV细胞）代表了浮游细菌组合的组成部分，包括当前代谢活跃的细胞和最近活跃的细胞。没有可见类核（non-NV）的细胞显得不活跃/休眠；然而，在适当的条件下，这些细胞可以发育出可见的类核，因此非nv细胞必须含有DNA。在沿海浮游细菌组合中，NV细胞的比例（20 ~ 60%）和单独鉴定为代谢活跃的细胞的比例（6% ~ 40%）比总细菌丰度变化更大。在常规基础上识别当前活跃和最近活跃的浮游细菌部分的能力可能提供令人兴奋的新成分，可以在较长的时间尺度（天-周）内整合细菌组合对环境变化的反应，而不是组合中当前活跃的部分（小时-天时间尺度）。此外，目前活跃的NV细胞的比例是NV细菌生长状态的潜在有价值的指标。这个项目代表了一个结合实验室和现场采样计划，以评估NV细胞与非NV细胞在浮游细菌组合中的影响。需要研究的思路包括：1)非nv细胞可以通过增加DNA/细胞的数量来形成可见的类核。2)与非NV细胞相比，NV细胞的放牧死亡率更高，这可以部分解释浮游细菌中无活性细胞的持久性。3)在沿海上升流系统中，浮游细菌组合的NV分量与自下而上控制（叶绿素-a浓度、细菌生产力）和自上而下控制（纳米鞭毛虫丰度、象菌体率）的关系比与总细菌丰度的关系更紧密。该研究项目的结果将对海洋浮游细菌如何响应控制其生长和海洋生物量的因素产生重要的新见解。＊＊＊

9633712 SHERR Heterotrophic bacteria process a large share of primary production in the sea, and are responsible for a significant portion of respiration and remineralization in marine food webs. Elucidating the roles of bacteria is thus essential to understanding the structure and functioning of marine ecosystems, particularly with respect to the role of marine biota in sequestering atmospheric carbon dioxide. A new epifluorescence, DNA staining method has revealed that bacterioplankton can be divided into two groups of cells: those with, and those without, visible nucleoids (as visualized by the method). Preliminary work suggests that cells with visible nucleoids (NV cells) represent the component of the bacterioplankton assemblage that includes both currently metabolically active and recently active cells. Cells without visible nucleoids (non-NV) appear to be inactive/dormant; however under appropriate conditions such cells can develop visible nucleoids, thus non-NV cells must contain DNA. In coastal bacterioplankton assemblages,the fraction of NV cells (20 ~ - 60%), and of cells separately identified as metabolically active (6% - 40%, was more variable than total bacterial abundance. The ability to identify the currently active + recently active portion of bacterioplankton on a routine basis may provide exciting new component can integrate the response of a bacterial assemblage to environmental change over longer time scales (days-weeks) than would the currently active fraction of the assemblage (time scale of hours-days). In addition, the ratio of currently active:NV cells is a potentially valuable index of the growth state of NV bacteria. This project represents a combined laboratory and field sampling program to evaluate the implications of NV versus non-NV cells in bacterioplankton assemblages. Ideas to be examined include: 1) Non-NV cells can develop visible nucleoids by increasing the amount of DNA/cell. 2) NV cells are subject to greater grazing mortality compared to non-NV cells, which could explain in part the persistence of inactive cells in bacterioplankton. 3) The NV component of bacterioplankton assemblages is more tightly coupled to indices of bottom-up control (chlorophyll-a concentration, bacterial productivity), and of top-down control (abundance of nanoflagellates, rate of bacterivory) than is total bacterial abundance in a coastal upwelling system. The results of this research project should yield important new insights concerning how marine bacterioplankton respond to factors controlling their growth and biomass in the sea. ***