Polyphosphates (polyP) are ubiquitous biomolecules that play a multitude of physiological roles in many cells. We have studied the presence and role of polyP in a unicellular alga, the freshwater diatom Achnanthidium minutissimum. This diatom stores up to 2.0 pg·cell⁻¹ of polyP, with chain lengths ranging from 130 to 500 inorganic phosphate units (P_i). We applied energy dispersive X-ray spectroscopy, Raman/fluorescence microscopy, and biochemical assays to localize and characterize the intracellular polyP granules that were present in large apical vacuoles. We investigated the fate of polyP in axenic A. minutissimum cells grown under phosphorus (P), replete (P₍₊₎), or P deplete (P₍₋₎) cultivation conditions and observed that in the absence of exogenous P, A. minutissimum rapidly utilizes their internal polyP reserves, maintaining their intrinsic growth rates for up to 8 days. PolyP-depleted A. minutissimum cells rapidly took up exogenous P a few hours after P_i resupply and generated polyP three times faster than cells that were not initially subjected to P limitation. Accordingly, we propose that A. minutissimum deploys a succession of acclimation strategies regarding polyP dynamics where the production or consumption of polyP plays a central role in the homeostasis of the diatom.

中文翻译：

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不同磷供应条件下广泛分布的淡水硅藻 Achnanthidium minutissimim 中多磷酸盐动态的表征

多磷酸盐 (polyP) 是普遍存在的生物分子，在许多细胞中发挥多种生理作用。我们研究了单细胞藻类（淡水硅藻 Achnanthidium minutissimum）中多聚磷的存在和作用。这种硅藻储存了高达2.0 pg·cell ^-1的polyP，其链长范围为130至500个无机磷酸盐单元(P _i )。我们应用能量色散 X 射线光谱、拉曼/荧光显微镜和生化测定来定位和表征大顶端液泡中存在的细胞内聚 P 颗粒。我们研究了在磷 (P)、充满磷 (P ₍₊₎ ) 或磷耗尽 (P _{(−) ) 培养条件下生长的无菌}A. minutissimum细胞中 PolyP 的命运，并观察到在缺乏外源 P 的情况下，A. minutissimum快速利用其内部 PolyP 储备，保持其内在增长率长达 8 天。PolyP 耗尽的微小A. minutissimum细胞在 P _i重新供应后几小时迅速吸收外源 P ，并且产生 PolyP 的速度比最初未受到 P 限制的细胞快三倍。因此，我们建议A. minutissimum部署了一系列有关 PolyP 动力学的驯化策略，其中 PolyP 的生产或消耗在硅藻的体内平衡中发挥着核心作用。