The model cyanobacterium Anabaena sp. PCC 7120 exhibits a phototrophic metabolism relying on oxygenic photosynthesis and a complex morphology. The organismic unit is a filament of communicated cells that may include cells specialized in different nutritional tasks, thus representing a paradigm of multicellular bacteria. In Anabaena, the inorganic carbon and nitrogen regime influenced not only growth, but also cell size, cell shape, and filament length, which also varied through the growth cycle. When using combined nitrogen, especially with abundant carbon, cells enlarged and elongated during active growth. When fixing N₂, which imposed lower growth rates, shorter and smaller cells were maintained. In Anabaena, gene homologs to mreB, mreC, and mreD form an operon that was expressed at higher levels during the phase of fastest growth. In an ntcA mutant, mre transcript levels were higher than in the wild type and, consistently, cells were longer. Negative regulation by NtcA can explain that Anabaena cells were longer in the presence of combined nitrogen than in diazotrophic cultures, in which the levels of NtcA are higher. mreB, mreC, and mreD mutants could grow with combined nitrogen, but only the latter mutant could grow diazotrophically. Cells were always larger and shorter than wild-type cells, and their orientation in the filament was inverted. Consistent with increased peptidoglycan width and incorporation in the intercellular septa, filaments were longer in the mutants, suggesting a role for MreB, MreC, and MreD in the construction of septal peptidoglycan that could affect intercellular communication required for diazotrophic growth.

中文翻译：

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无机营养体系和 mre 基因调节光养多细胞鱼腥藻中的细胞和细丝大小和形态

模型蓝藻Anabaena sp。PCC 7120 表现出依赖于有氧光合作用的光养代谢和复杂的形态。有机体单元是一条由通讯细胞组成的细丝，其中可能包括专门从事不同营养任务的细胞，因此代表了多细胞细菌的范例。在鱼腥藻中，无机碳和氮状态不仅影响生长，而且影响细胞大小、细胞形状和细丝长度，它们也在生长周期中发生变化。当使用结合氮时，尤其是在碳含量丰富的情况下，细胞在活跃生长过程中会变大和伸长。当固定 N _{2 时}，它施加了较低的生长速率，维持了更短和更小的细胞。在鱼腥藻中，基因同系物mreB、mreC和mreD形成一个操纵子，在生长最快的阶段表达水平较高。在NTCA突变，MRE转录水平比野生型更高，始终如一，细胞更长的时间。NtcA 的负调节可以解释鱼腥藻细胞在结合氮存在下比在固氮培养中更长的时间，其中 NtcA 的水平更高。mreB、mreC和mreD突变体可以与结合氮一起生长，但只有后一个突变体可以固氮生长。细胞总是比野生型细胞更大更短，并且它们在细丝中的方向是颠倒的。与增加的肽聚糖宽度和细胞间隔膜中的掺入一致，突变体中的细丝更长，这表明 MreB、MreC 和 MreD 在构建隔膜肽聚糖中的作用可能会影响固氮生长所需的细胞间通讯。