Patterns and Mechanisms of Variability in the Physiological State of Bacteria in Marine Pelagic Environments

细菌在水生生态系统中转化有机碳的作用被认为仅次于浮游植物。据报道，在开阔的海洋水域，细菌的生物量超过了所有其他浮游生物的生物量，甚至在大陆架和沿海水域，与其他浮游生物相比，细菌的生物量也很大。然而，这些估计都是基于所有dapi染色的细胞都是代谢活跃细胞的假设。这种假设似乎不再站得住脚：大部分表面上的细菌要么是不活跃的，要么是垂死的，要么是死亡的。这样的结论有可能促成生态系统功能概念模型的另一个范式转变。至少，这意味着，在给定的时间内，相对较少的细菌在原位生长（和呼吸）比以前想象的要快得多，并且相当一部分dapi染色的细菌要么表现出低活性，要么是碎屑的组成部分。荧光染色和分子探针的一种新组合已经被开发出来，它可以定量地鉴定那些膜受损的细胞，以及那些含有足够的rRNA被认为是代谢活跃的细胞。虽然这两种方法都不足以从无活性、垂死或死亡的细胞中确定活性细胞，但它们共同构成了一个强大的工具，可以研究这些细胞类型在原位的相对重要性，并假设在给定的时间和地点，哪些细菌死亡或刺激来源可能是重要的。最近和持续的研究已经彻底评估并证实了生命染色探针（VSP）方法在定量和明确区分活细胞、非活细胞和低活性细胞方面的适用性。在一项相关但独立的研究中，还开发了一种定量技术来确定碎屑的浓度，操作上定义为悬浮无生命POC。这些努力包括新开发的图像分析协议和算法，以识别和枚举不同组的VSP细胞，以及游离和附着的细菌。在这里，机制研究将探讨环境参数对细菌VSP染色模式的影响；进行季节性样带，以确定天然细菌群落在生产力和碎屑梯度上的生理状态；并测量自然群落和相关碎屑对美国东南外大陆架上升流诱导的浮游植物大量繁殖的时间依赖性响应。特别感兴趣的是评估生物学意义（如果有的话）和代谢活跃人群比例变化的触发因素。最终，重要的可能不在于是40%还是60%的群落是活跃的，而在于特定的官能团是活跃的还是增长缓慢的，例如硝酸盐还原剂。要解决这些问题，首先必须回答这里提出的问题。此外，该结果将提供一个独特的现场数据集，以评估细菌在DOC，碎屑和细菌之间转化中的作用的当前概念模型。

Frischer 9906734Bacteria are thought to be second only to phytoplankton in their role of transforming organic carbon in aquatic ecosystems. In open ocean waters, the biomass of bacteria has been reported to exceed that of all other living plankton, and even in continental shelf and coastal waters it is significant compared to other plankton. However, these estimates are all derived from the assumption that all DAPI-stained cells are metabolically active cells. This hypothesis no longer appears tenable: a large fraction of apparent bacteria are either inactive, moribund, or dead. Such a conclusion threatens to precipitate another paradigm shift in conceptual models of ecosystem function. At the very least, it would imply that, at a given time, comparatively few bacteria in situ are growing (and respiring) much faster than previously thought, and that a substantial fraction of DAPI-stained bacteria either exhibit low activity or are operationally a component of detritus.A novel combination of a fluorescent stain and molecular probes has been developed which quantitatively identify those cells with compromised membranes, and those cells containing sufficient rRNA to be considered metabolically active. While neither approach might be considered sufficient to specify active from inactive, moribund, or dead cells, together they comprise a powerful tool to investigate the relative importance of these cell types in situ, and to postulate which sources of bacterial mortality or stimulation may be important at a given time and place. Recent and continuing studies have thoroughly evaluated and confirmed the applicability of the vital stain and probe (VSP) method to quantitatively and unambiguously discriminate among living, nonliving, and low activity cells. In a related but separate study, a quantitative technique also has been developed to determine concentrations of detritus, operationally defined as suspended nonliving POC. These efforts include newly developed image analysis protocols and algorithms to recognize and enumerate the different groups of VSP cells, and also free vs. attached bacteria.Here, mechanistic studies will investigate the effects of environmental parameters on patterns of VSP staining of bacteria; conduct seasonal transects to determine the physiological status of natural bacterial communities across a productivity and detritus gradient; and measure the time-dependent response of natural communities and associated detritus to upwelling-induced phytoplankton blooms on the outer U.S. southeastern continental shelf. Of special interest are evaluating the biological significance (if any) and the triggers of shifts in the fraction of metabolically active populations. Ultimately, the significance may not lie in whether it is 40% vs. 60% of a community which is active, but whether specific functional groups are active or slow growing, e.g. nitrate reducers. To address such issues, the questions posed here must first be answered. Moreover, the results will provide a unique field dataset to evaluate current conceptual models of the role of bacteria in transformations between DOC, detritus, and bacteria.