Berman-Frank Ilana, Rosenberg Gad, Levitan Orly, Haramaty Liti, Mari Xavier
Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, 52900, Israel.
Environ Microbiol. 2007 Jun;9(6):1415-22. doi: 10.1111/j.1462-2920.2007.01257.x.
Extracellular polysaccharide aggregates, operationally defined as transparent exopolymeric particles (TEP), are recognized as an important conduit for carbon recycling and export in aquatic systems. Yet, the factors controlling the build-up of the TEP pool are not well characterized. Here we show that increased TEP production by Trichodesmium, an oceanic bloom-forming nitrogen-fixing (diazotrophic) cyanobacterium, is coupled with autocatalytic programmed cell death (PCD) process. We demonstrate that PCD induction, in both laboratory cultures and natural populations, is characterized by high caspase-like activity, correlates with enhanced TEP production, and occurs under iron and phosphorus starvation, as well as under high irradiance and oxidative stress. Enhanced TEP production was not observed in actively growing populations. We provide further evidence that iron is a key trigger for the induction of PCD. We demonstrate, for the first time, the concomitant enhanced build-up of the TEP pool when Trichodesmium is Fe-stressed. These results suggest a functional linkage between activation of caspases and PCD in Trichodesmium and regulation of vertical carbon and nitrogen fluxes. We hypothesize that modulation of TEP formation and its qualities by different mortality pathways could regulate the fate of phytoplankton blooms and particulate organic matter in aquatic ecosystems.
细胞外多糖聚集体，在操作上定义为透明胞外聚合物颗粒（TEP），被认为是水生系统中碳循环和输出的重要途径。然而，控制TEP库积累的因素尚未得到很好的表征。在这里，我们表明，海洋中形成水华的固氮（固氮营养型）蓝细菌束毛藻增加TEP的产生与自催化程序性细胞死亡（PCD）过程有关。我们证明，在实验室培养和自然种群中，PCD诱导的特征是高半胱天冬酶样活性，与增强的TEP产生相关，并发生在铁和磷饥饿以及高辐照度和氧化应激条件下。在活跃生长的种群中未观察到TEP产生增强。我们提供了进一步的证据，表明铁是诱导PCD的关键触发因素。我们首次证明，当束毛藻受到铁胁迫时，TEP库会同时增强积累。这些结果表明，束毛藻中半胱天冬酶的激活和PCD与垂直碳和氮通量的调节之间存在功能联系。我们假设，不同死亡途径对TEP形成及其质量的调节可能会影响水生生态系统中浮游植物水华和颗粒有机物的命运。
