Molecular Diffusion through Cyanobacterial Septal Junctions.
Molecular Diffusion through Cyanobacterial Septal Junctions.
复制标题
DOI：
10.1128/mbio.01756-16
复制
发表时间：
2017-01-03
期刊：
影响因子：
6.4
通讯作者：
Flores E
中科院分区：
文献类型：
--
作者：
Nieves-Morión M;Mullineaux CW;Flores E
形成异囊的蓝细菌以丝状生长，其中发生细胞间分子交换。在 N2 固定异形细胞的分化过程中，调节因子在细胞之间转移。在固氮丝中，营养细胞通过含氧光合作用固定二氧化碳，为异形细胞提供减少的碳，而异形细胞为营养细胞提供固定的氮。细胞间分子转移已用荧光标记物进行追踪，包括钙黄绿素、5-羧基荧光素和蔗糖类似物七叶苷，观察到这些荧光标记物的浓度梯度向下移动。在这项工作中，我们在模型异囊形成蓝藻鱼腥藻中使用了光漂白后荧光恢复（FRAP）测定。菌株 PCC 7120 测量荧光标记细胞间转移的温度依赖性。我们发现传输速率常数与绝对温度成正比。这表明连接丝中细胞的“间隔连接”（以前称为“微胞间连丝”）允许通过简单扩散进行分子交换，而无需任何激活的中间状态。除了先前表征的主动运输和促进扩散机制之外，这构成了穿过细菌细胞质膜的分子转移的新机制。蓝藻隔膜连接在功能上类似于后生动物的间隙连接。尽管细菌通常被认为是单细胞生物，但也有一些细菌表现得像真正的多细胞生物。形成异形囊的蓝细菌以细丝的形式生长，细胞在细丝中进行交流。细胞间分子交换被认为是由隔膜连接介导的。在这里，我们证明了蓝藻丝中荧光标记的细胞间转移具有简单扩散的物理特性。因此，蓝藻隔膜连接在功能上类似于后生动物间隙连接，尽管它们的分子成分似乎不相关。与后生动物间隙连接一样，蓝细菌的隔膜连接允许小分子在细胞间快速交换，而没有严格的选择性。我们的发现扩展了原核生物跨质膜分子转移机制的全部内容。
Heterocyst-forming cyanobacteria grow as filaments in which intercellular molecular exchange takes place. During the differentiation of N2-fixing heterocysts, regulators are transferred between cells. In the diazotrophic filament, vegetative cells that fix CO2 through oxygenic photosynthesis provide the heterocysts with reduced carbon and heterocysts provide the vegetative cells with fixed nitrogen. Intercellular molecular transfer has been traced with fluorescent markers, including calcein, 5-carboxyfluorescein, and the sucrose analogue esculin, which are observed to move down their concentration gradient. In this work, we used fluorescence recovery after photobleaching (FRAP) assays in the model heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 to measure the temperature dependence of intercellular transfer of fluorescent markers. We find that the transfer rate constants are directly proportional to the absolute temperature. This indicates that the “septal junctions” (formerly known as “microplasmodesmata”) linking the cells in the filament allow molecular exchange by simple diffusion, without any activated intermediate state. This constitutes a novel mechanism for molecular transfer across the bacterial cytoplasmic membrane, in addition to previously characterized mechanisms for active transport and facilitated diffusion. Cyanobacterial septal junctions are functionally analogous to the gap junctions of metazoans. Although bacteria are frequently considered just as unicellular organisms, there are bacteria that behave as true multicellular organisms. The heterocyst-forming cyanobacteria grow as filaments in which cells communicate. Intercellular molecular exchange is thought to be mediated by septal junctions. Here, we show that intercellular transfer of fluorescent markers in the cyanobacterial filament has the physical properties of simple diffusion. Thus, cyanobacterial septal junctions are functionally analogous to metazoan gap junctions, although their molecular components appear unrelated. Like metazoan gap junctions, the septal junctions of cyanobacteria allow the rapid intercellular exchange of small molecules, without stringent selectivity. Our finding expands the repertoire of mechanisms for molecular transfer across the plasma membrane in prokaryotes.