ABSTRACT A new marine strain of picoplanktonic algae, PMPFPPE4, was isolated from a mixed net-phytoplankton sample taken from the upper euphotic layer of the southeastern Adriatic Sea. Evaluation of the new strain included morphological investigation (by light and electron microscopy), phylogenetic analysis (utilizing plastid 16S rRNA and nuclear 18S rRNA genes), and physiological characterization (screening of pigment/lipid composition and capturing photosynthesis measurements). The new strain was proven to belong to the genus Picochlorum and the lipid composition revealed an unexpected accumulation of triacylglycerols, indicating an evolutionary adaptation for growth under unfavourable conditions. In addition, lipid remodelling in the exponential to stationary growth phase was characterized by an increased share of membrane-forming digalactosyldiacylglycerols and phosphatidylcholines. Maximum photosynthetic activity measured was at 30°C, but the most rapid increase of photosynthetic activity was at lower temperatures (15–20°C). Moreover, the thermotolerant strain did not exhibit photoinhibition below 40°C and survived a one-month cultivation period in complete darkness. The strain’s survival in low light and dark conditions suggests a potential shift from autotrophy to mixotrophy under unfavourable growth conditions. Thus, the unique physiological attributes represented by a high growth rate, thermotolerance, phototolerance and high triacylglycerol synthesis may render the strain highly attractive for biofuel production and growth in large outdoor systems.

中文翻译：

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Picochlorum 属（Trebouxiophyceae）产脂耐热海洋光合微微藻的表征

摘要 从亚得里亚海东南部透光层上层的混合净浮游植物样本中分离出一种新的海洋微浮游藻菌株 PMPFPPE4。新菌株的评估包括形态学研究（通过光学和电子显微镜）、系统发育分析（利用质体 16S rRNA 和核 18S rRNA 基因）和生理特征（色素/脂质成分的筛选和捕获光合作用测量）。新菌株被证明属于 Picochlorum 属，脂质成分显示出意外的三酰甘油积累，表明在不利条件下进化适应生长。此外，在指数到稳定生长期中脂质重塑的特征是成膜二半乳糖二酰基甘油和磷脂酰胆碱的份额增加。测得的最大光合活性在 30°C 时，但光合活性增加最快的是在较低温度（15-20°C）下。此外，该耐热菌株在 40°C 以下不表现出光抑制作用，并在完全黑暗中存活了 1 个月的培养期。该菌株在弱光和黑暗条件下的存活表明在不利的生长条件下可能从自养向混合营养转变。因此，以高增长率、耐热性、