Benthic animals inhabiting the edges of marine oxygen minimum zones (OMZ) are exposed to unpredictable large fluctuations of oxygen levels. Sessile organisms including bivalves must depend on physiological adaptations to withstand these conditions. However, as habitats are rather inaccessible, physiological adaptations of the OMZ margin inhabitants to oxygen fluctuations are not well understood. We therefore investigated the transcriptional responses of selected key genes involved in energy metabolism and stress protection in a dominant benthic species of the northern edge of the Namibian OMZ, the nuculanid clam Lembulus bicuspidatus,. We exposed clams to normoxia (~5.8 ml O₂ l⁻¹), severe hypoxia (36 h at ~0.01 ml O₂ l⁻¹) and post-hypoxic recovery (24 h of normoxia following 36 h of severe hypoxia). Using newly identified gene sequences, we determined the transcriptional responses to hypoxia and reoxygenation of the mitochondrial aerobic energy metabolism (pyruvate dehydrogenase E1 complex, cytochrome c oxidase, citrate synthase, and adenine nucleotide translocator), anaerobic glycolysis (hexokinase (HK), phosphoenolpyruvate carboxykinase (PEPCK), phosphofructokinase, and aldolase), mitochondrial antioxidants (glutaredoxin, peroxiredoxin, and uncoupling protein UCP2) and stress protection mechanisms (a molecular chaperone HSP70 and a mitochondrial quality control protein MIEAP) in the gills and the labial palps of L. bicuspidatus. Exposure to severe hypoxia transcriptionally stimulated anaerobic glycolysis (including HK and PEPCK), antioxidant protection (UCP2), and quality control mechanisms (HSP70 and MIEAP) in the gills of L. bicuspidatus. Unlike UCP2, mRNA levels of the thiol-dependent mitochondrial antioxidants were not affected by hypoxia-reoxygenation stress. Transcript levels of marker genes for aerobic energy metabolism were not responsive to oxygen fluctuations in L. bicuspidatus. Our findings highlight the probable importance of anaerobic succinate production (via PEPCK) and mitochondrial and proteome quality control mechanisms in responses to oxygen fluctuations of the OMZ bivalve L. bicuspidatus. The reaction of L. bicuspidatus to oxygen fluctuations implies parallels to that of other hypoxia-tolerant bivalves, such as intertidal species.

栖息在海洋最低氧区 (OMZ) 边缘的底栖动物暴露于不可预测的氧气水平大幅波动。包括双壳类在内的固着生物必须依靠生理适应来承受这些条件。然而，由于栖息地相当难以进入，OMZ 边缘居民对氧气波动的生理适应尚不清楚。因此，我们研究了纳米比亚 OMZ 北部边缘优势底栖物种Lembulus bicuspidatus 中涉及能量代谢和应激保护的选定关键基因的转录反应。我们将蛤蜊暴露于常氧（~5.8 ml O ₂ l ^-1）、严重缺氧（~0.01 ml O ₂ l ^{-1 下}36 小时））和缺氧后恢复（严重缺氧 36 小时后 24 小时常氧）。使用新鉴定的基因序列，我们确定了线粒体有氧能量代谢（丙酮酸脱氢酶 E1 复合物、细胞色素 c 氧化酶、柠檬酸合酶和腺嘌呤核苷酸转运蛋白）、无氧糖酵解（己糖激酶 (HK)、磷酸烯醇）对缺氧和再充氧的转录反应丙酮酸羧激酶（PEPCK）、磷酸果糖激酶和醛缩酶）、线粒体抗氧化剂（谷氧还蛋白、过氧还蛋白和解偶联蛋白 UCP2）和鳃和唇部的压力保护机制（分子伴侣 HSP70 和线粒体质量控制蛋白 MIEAP） .二尖瓣. 暴露于严重缺氧会转录刺激 L. bicuspidatus鳃中的无氧糖酵解（包括 HK 和 PEPCK）、抗氧化保护 (UCP2) 和质量控制机制（HSP70 和 MIEAP）。与 UCP2 不同，硫醇依赖性线粒体抗氧化剂的 mRNA 水平不受缺氧-复氧应激的影响。有氧能量代谢标记基因的转录水平对 L. bicuspidatus 中的氧气波动没有反应。我们的研究结果强调了厌氧琥珀酸生产（通过 PEPCK）以及线粒体和蛋白质组质量控制机制对 OMZ 双壳类L. bicuspidatus氧波动的可能重要性。L. bicuspidatus的反应 氧气波动意味着与其他耐缺氧双壳类动物（例如潮间带物种）的波动相似。