ABSTRACT

As a major component of coastal phytoplankton blooms, diatoms are an important source of dissolved organic matter (DOM) in the ocean. While this DOM pool fuels the growth of diverse bacterial populations, diatom population dynamics itself is considered unaffected by it. Here, we identified strong negative effects of the amino acid asparagine on the growth of the marine model diatom Phaeodactylum tricornutum. Using microscopic analyses and physiological assays, we showed that while asparagine fuelled photosynthetic growth, its supplementation to NO₃⁻ medium significantly decreased the culture’s cell density and photosynthetic capacity (F_v/F_m) during the stationary phase of the growth cycle. We further showed that these effects resulted from asparagine-based production of hydrogen peroxide (H₂O₂) that triggered a massive cell death event. Effective lethal asparagine concentrations were as low as 12.5 µM, while 1 μM affected F_v/F_m, but did not trigger culture collapse. Based on sequence similarity with the characterized H₂O₂-producing L-amino acid oxidase (LAAO) of Chlamydomonas reinhardtii, LAO1, we identified putative LAO1 orthologs in the genomes of P. tricornutum and the toxigenic pennate species Pseudo-nitzschia multiseries. The molecular phylogeny of this gene indicates a shared ancestry with other algal LAAOs and suggests a conserved oxidative deaminase function that could mediate DOM release from diatom populations through the triggering of autocatalytic cell death events.

抽象的

作为沿海浮游植物开花的主要组成部分，硅藻是海洋中溶解性有机物（DOM）的重要来源。尽管此DOM池为各种细菌种群的增长提供了动力，但硅藻种群动态本身本身不受其影响。在这里，我们确定了氨基酸天冬酰胺对海洋模型硅藻Phaeodactylum tricornutum生长的强烈负面影响。使用显微镜分析和生理测定法，我们发现，天冬酰胺，而燃料光合生长，其补充到NO ₃ ^-介质显著降低培养的细胞密度和光合能力（F _v / F_米）在生长周期的稳定阶段。我们进一步表明，这些效应是由基于天冬酰胺的过氧化氢（H ₂ O ₂）产生而引发的大规模细胞死亡事件。有效的致命天冬酰胺浓度低至12.5 µM，而1 µM影响F _v / F _m，但不会触发培养物崩溃。基于与莱茵衣藻LAO1的特征性产生H ₂ O _2的L-氨基酸氧化酶（LAAO）的序列相似性，我们确定了三角果假单胞菌和产毒的戊二烯类假奈瑟菌多基因组的基因组中推定的LAO1直系同源物。。该基因的系统发育史表明其与其他藻类LAAO有共同的血统，并暗示了保守的氧化脱氨酶功能，该功能可以通过触发自催化细胞死亡事件来介导硅藻种群中DOM的释放。