Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, 405 Hilgard Ave., Los Angeles, CA 90095-1569, USA.
J Bacteriol. 2010 Feb;192(3):819-33. doi: 10.1128/JB.01240-09. Epub 2009 Nov 30.
In a developmental strategy designed to efficiently exploit and colonize sparse oligotrophic environments, Caulobacter crescentus cells divide asymmetrically, yielding a motile swarmer cell and a sessile stalked cell. After a relatively fixed time period under typical culture conditions, the swarmer cell differentiates into a replicative stalked cell. Since differentiation into the stalked cell type is irreversible, it is likely that environmental factors such as the availability of essential nutrients would influence the timing of the decision to abandon motility and adopt a sessile lifestyle. We measured two different parameters in nutrient-limited chemostat cultures, biomass concentration and the ratio of nonstalked to stalked cells, over a range of flow rates and found that nitrogen limitation significantly extended the swarmer cell life span. The transcriptional profiling experiments described here generate the first comprehensive picture of the global regulatory strategies used by an oligotroph when confronted with an environment where key macronutrients are sparse. The pattern of regulated gene expression in nitrogen- and carbon-limited cells shares some features in common with most copiotrophic organisms, but critical differences suggest that Caulobacter, and perhaps other oligotrophs, have evolved regulatory strategies to deal distinctly with their natural environments. We hypothesize that nitrogen limitation extends the swarmer cell lifetime by delaying the onset of a sequence of differentiation events, which when initiated by the correct combination of external environmental cues, sets the swarmer cell on a path to differentiate into a stalked cell within a fixed time period.
在一项旨在高效利用和殖民贫瘠寡营养环境的发展策略中，新月柄杆菌细胞不对称分裂，产生一个游动的泳动细胞和一个固着的柄细胞。在典型培养条件下经过相对固定的时间后，泳动细胞分化为复制的柄细胞。由于分化为柄细胞类型是不可逆的，因此环境因素（如必需营养物质的可用性）可能会影响放弃运动和采用固着生活方式的决策时机。我们在营养限制的恒化器培养物中测量了两个不同的参数，即在一系列流速下的生物量浓度和非柄细胞与柄细胞的比例，并发现氮限制显著延长了泳动细胞的寿命。这里描述的转录谱实验生成了一个寡营养生物在关键宏量营养素稀缺的环境中所使用的全局调控策略的第一个全面图像。氮和碳限制细胞中受调控基因表达的模式与大多数富营养生物有一些共同特征，但关键差异表明，新月柄杆菌，也许还有其他寡营养生物，已经进化出了调控策略来应对其自然环境。我们假设氮限制通过延迟一系列分化事件的开始来延长泳动细胞的寿命，这些事件一旦被正确组合的外部环境线索触发，就会使泳动细胞在固定时间内分化为柄细胞。
