Table_5_Elevated inorganic carbon and salinity enhances photosynthesis and ATP synthesis in picoalga Picocystis salinarum as revealed by label free quantitative proteomics.XLSX

Saline soda lakes are of immense ecological value as they niche some of the most exclusive haloalkaliphilic communities dominated by bacterial and archaeal domains, with few eukaryotic algal representatives. A handful reports describe Picocystis as a key primary producer with great production rates in extremely saline alkaline habitats. An extremely haloalkaliphilic picoalgal strain, Picocystis salinarum SLJS6 isolated from hypersaline soda lake Sambhar, Rajasthan, India, grew robustly in an enriched soda lake medium containing mainly Na2CO3, 50 g/l; NaHCO3, 50 g/l, NaCl, 50 g/l (salinity ≈150‰) at pH 10. To elucidate the molecular basis of such adaptation to high inorganic carbon and NaCl concentrations, a high-throughput label-free quantitation based quantitative proteomics approach was applied. Out of the total 383 proteins identified in treated samples, 225 were differentially abundant proteins (DAPs), of which 150 were statistically significant (p < 0.05) including 70 upregulated and 64 downregulated proteins after 3 days of growth in highly saline-alkaline medium. Most DAPs were involved in photosynthesis, oxidative phosphorylation, glucose metabolism and ribosomal structural components envisaging that photosynthesis and ATP synthesis were central to the salinity-alkalinity response. Key components of photosynthetic machinery like photosystem reaction centres, adenosine triphosphate (ATP) synthase ATP, Rubisco, Fructose-1,6-bisphosphatase, Fructose-bisphosphate aldolase were highly upregulated. Enzymes peptidylprolyl isomerases (PPIase), important for correct protein folding showed remarkable marked-up regulation along with other chaperon proteins indicating their role in osmotic adaptation. Enhanced photosynthetic activity exhibited by P. salinarum in highly saline-alkaline condition is noteworthy as photosynthesis is suppressed under hyperosmotic conditions in most photosynthetic organisms. The study provided the first insights into the proteome of extremophilic alga P. salinarum exhibiting extraordinary osmotic adaptation and proliferation in polyextreme conditions prevailing in saline sodic ecosystems, potentially unraveling the basis of resilience in this not so known organism and paves the way for a promising future candidate for biotechnological applications and model organism for deciphering the molecular mechanisms of osmotic adaptation. The mass spectrometry proteomics data is available at the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD037170.

苏打盐湖具有极高的生态价值，它们为以细菌域、古菌域为主的专属嗜盐嗜碱（haloalkaliphilic）群落提供了独特生境，其中真核藻类代表类群极少。现有少量研究表明，皮胆球藻属（Picocystis）是极端盐碱性生境中的关键初级生产者，具有极高的生产力。研究人员从印度拉贾斯坦邦桑布尔高盐苏打湖中分离得到一株极端嗜盐嗜碱微藻菌株——盐生皮胆球藻（Picocystis salinarum）SLJS6，该菌株在主要成分为Na₂CO₃ 50g/L、NaHCO₃ 50g/L、NaCl 50g/L（盐度≈150‰）、pH 10的富集型苏打湖培养基中生长旺盛。为阐明其对高无机碳与NaCl浓度的适应分子机制，本研究采用了基于高通量无标记定量的蛋白质组学分析方法。经处理的样本中共鉴定出383种蛋白质，其中225种为差异丰度蛋白（differentially abundant proteins, DAPs）；在高盐碱性培养基中培养3天后，150种差异丰度蛋白具有统计学显著性（p < 0.05），包括70种上调蛋白与64种下调蛋白。多数差异丰度蛋白参与光合作用、氧化磷酸化、葡萄糖代谢以及核糖体结构组分，表明光合作用与ATP合成是盐碱性胁迫应答的核心通路。光合机制的关键组分如光系统反应中心、ATP合酶（adenosine triphosphate (ATP) synthase）、核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）、果糖-1,6-二磷酸酶（Fructose-1,6-bisphosphatase）、果糖二磷酸醛缩酶（Fructose-bisphosphate aldolase）均呈现高度上调。肽基脯氨酰异构酶（peptidylprolyl isomerases, PPIase）作为协助蛋白质正确折叠的关键酶，与其他分子伴侣蛋白一同表现出显著的上调表达，提示其在渗透适应过程中发挥重要作用。值得注意的是，盐生皮胆球藻（P. salinarum）在高盐碱性条件下仍可维持增强的光合活性，而在多数光合生物中，高渗环境会抑制光合作用过程。本研究首次揭示了极端嗜藻类盐生皮胆球藻的蛋白质组特征，该物种在苏打盐湖生态系统的多重极端条件下展现出优异的渗透适应与增殖能力，有望为解析这一鲜为人知物种的抗逆机制提供新视角，同时为其作为生物技术应用的潜在候选物种以及解析渗透适应分子机制的模式生物奠定了基础。本研究产生的质谱蛋白质组学数据已通过PRIDE合作伙伴库提交至ProteomeXchange联盟，数据集标识符为PXD037170。