Cohen Assaf, Sendersky Eleonora, Carmeli Shmuel, Schwarz Rakefet
The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
Department of Chemistry, Tel-Aviv University, Israel.
PLoS One. 2014 Jun 24;9(6):e100747. doi: 10.1371/journal.pone.0100747. eCollection 2014.
Phytoplankton mortality allows effective nutrient cycling, and thus plays a pivotal role in driving biogeochemical cycles. A growing body of literature demonstrates the involvement of regulated death programs in the abrupt collapse of phytoplankton populations, and particularly implicates processes that exhibit characteristics of metazoan programmed cell death. Here, we report that the cell-free, extracellular fluid (conditioned medium) of a collapsing aged culture of the cyanobacterium Synechococcus elongatus is toxic to exponentially growing cells of this cyanobacterium, as well as to a large variety of photosynthetic organisms, but not to eubacteria. The toxic effect, which is light-dependent, involves oxidative stress, as suggested by damage alleviation by antioxidants, and the very high sensitivity of a catalase-mutant to the conditioned medium. At relatively high cell densities, S. elongatus cells survived the deleterious effect of conditioned medium in a process that required de novo protein synthesis. Application of conditioned medium from a collapsing culture caused severe pigment bleaching not only in S. elongatus cells, but also resulted in bleaching of pigments in a cell free extract. The latter observation indicates that the elicited damage is a direct effect that does not require an intact cell, and therefore, is mechanistically different from the metazoan-like programmed cell death described for phytoplankton. We suggest that S. elongatus in aged cultures are triggered to produce a toxic compound, and thus, this process may be envisaged as a novel regulated death program.
浮游植物的死亡促进了有效的养分循环，因此在推动生物地球化学循环中起着关键作用。越来越多的文献表明，受调控的死亡程序参与了浮游植物种群的突然崩溃，特别是涉及表现出后生动物程序性细胞死亡特征的过程。在此，我们报告，衰老的聚球藻培养物崩溃时的无细胞细胞外液（条件培养基）对该蓝藻的指数生长期细胞以及多种光合生物有毒，但对真细菌无毒。这种毒性作用依赖于光，涉及氧化应激，抗氧化剂减轻损伤以及过氧化氢酶突变体对条件培养基的极高敏感性表明了这一点。在相对较高的细胞密度下，聚球藻细胞在一个需要从头合成蛋白质的过程中幸免于条件培养基的有害影响。应用崩溃培养物的条件培养基不仅导致聚球藻细胞严重色素漂白，还导致无细胞提取物中的色素漂白。后一观察结果表明，引发的损伤是一种直接效应，不需要完整的细胞，因此，在机制上不同于描述的浮游植物类后生动物程序性细胞死亡。我们认为，衰老培养物中的聚球藻被触发产生一种有毒化合物，因此，这个过程可以被设想为一种新的受调控的死亡程序。
