Many cyanobacteria produce extracellular polymeric substances (EPS), composed mainly of heteropolysaccharides, that play a variety of physiological roles, being crucial for cell protection, motility, and biofilm formation. However, due to their complexity, the EPS biosynthetic pathways as well as their assembly and export mechanisms are still far from being fully understood. Here, we show that the absence of a putative EPS-related protein, KpsM (Slr0977), has a pleiotropic effect on Synechocystis sp. strain PCC 6803 physiology, with a strong impact on the export of EPS and carbon fluxes. The kpsM mutant exhibits a significant reduction of released polysaccharides and a smaller decrease of capsular polysaccharides, but it accumulates more polyhydroxybutyrate (PHB) than the wild type. In addition, this strain shows a light/cell density-dependent clumping phenotype and exhibits an altered protein secretion capacity. Furthermore, the most important structural component of pili, the protein PilA, was found to have a modified glycosylation pattern in the mutant compared to the wild type. Proteomic and transcriptomic analyses revealed significant changes in the mechanisms of energy production and conversion, namely, photosynthesis, oxidative phosphorylation, and carbon metabolism, in response to the inactivation of slr0977. Overall, this work shows for the first time that cells with impaired EPS secretion undergo transcriptomic and proteomic adjustments, highlighting the importance of EPS as a major carbon sink in cyanobacteria. The accumulation of PHB in cells of the mutant, without affecting significantly its fitness/growth rate, points to its possible use as a chassis for the production of compounds of interest.

中文翻译：

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KpsM (Slr0977) 的缺失会损害胞外聚合物 (EPS) 的分泌并影响集胞藻中的碳通量。 PCC 6803


许多蓝藻产生胞外聚合物（EPS），主要由杂多糖组成，发挥多种生理作用，对细胞保护、运动和生物膜形成至关重要。然而，由于其复杂性，EPS生物合成途径及其组装和输出机制仍远未被完全了解。在这里，我们表明，假定的 EPS 相关蛋白 KpsM (Slr0977) 的缺失对集胞藻具有多效性作用。 PCC 6803 菌株的生理学，对 EPS 和碳通量的输出有很大影响。 kpsM突变体表现出释放多糖的显着减少和荚膜多糖的减少较小，但它比野生型积累了更多的聚羟基丁酸酯（PHB）。此外，该菌株显示出光/细胞密度依赖性聚集表型，并表现出改变的蛋白质分泌能力。此外，与野生型相比，突变体中菌毛最重要的结构成分蛋白质 PilA 的糖基化模式发生了改变。蛋白质组学和转录组学分析揭示了slr0977失活导致能量产生和转化机制（即光合作用、氧化磷酸化和碳代谢）发生显着变化。总体而言，这项工作首次表明 EPS 分泌受损的细胞经历转录组和蛋白质组调整，强调了 EPS 作为蓝藻主要碳汇的重要性。 PHB 在突变体细胞中的积累，不会显着影响其适应度/生长率，表明其可能用作生产感兴趣的化合物的底盘。