Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
Nat Commun. 2024 Oct 12;15(1):8825. doi: 10.1038/s41467-024-53205-5.
Sea cucumbers are predominant deposit feeders in benthic ecosystems, providing protective benefits to coral reefs by reducing disease prevalence. However, how they receive sufficient nutrition from seabed sediments remains poorly understood. Here, we investigate Holothuria leucospilota, an ecologically significant tropical sea cucumber, to elucidate digestive mechanisms underlying marine deposit-feeding. Genomic analysis reveals intriguing evolutionary adaptation characterized by an expansion of digestive carbohydrase genes and a contraction of digestive protease genes, suggesting specialization in digesting microalgae. Developmentally, two pivotal dietary shifts, namely, from endogenous nutrition to planktonic feeding, and from planktonic feeding to deposit feeding, induce changes in digestive tract enzyme profiles, with adults mainly expressing carbohydrases and lipases. A nuanced symbiotic relationship exists between gut microbiota and the host, namely, specific resident bacteria supply crucial enzymes for food digestion, while other bacteria are digested and provide assimilable nutrients. Our study further identifies Holothuroidea lineage-specific lysozymes that are restrictedly expressed in the intestines to support bacterial digestion. Overall, this work advances our knowledge of the evolutionary innovations in the sea cucumber digestive system which enable them to efficiently utilize nutrients from seabed sediments and promote food recycling within marine ecosystems.
海参是底栖生态系统中主要的沉积物食性动物，通过降低疾病流行率为珊瑚礁提供保护益处。然而，它们如何从海底沉积物中获得足够的营养仍然知之甚少。在这里，我们研究了生态上重要的热带海参糙海参，以阐明海洋沉积物食性的消化机制。基因组分析揭示了有趣的进化适应特征，即消化碳水化合物酶基因的扩张和消化蛋白酶基因的收缩，表明其在消化微藻方面具有专业化。在发育过程中，经历了从内源性营养到浮游生物摄食，再到沉积物摄食的两个关键的饮食转变，导致消化道酶谱发生变化，成年海参主要表达碳水化合物酶和脂肪酶。肠道微生物群与宿主之间存在着微妙的共生关系，即特定的常驻细菌提供了用于食物消化的关键酶，而其他细菌则被消化并提供可吸收的营养。我们的研究进一步鉴定了Holothuroidea 谱系特异性溶菌酶，这些酶仅在肠道中表达，以支持细菌消化。总的来说，这项工作增进了我们对海参消化系统进化创新的认识，使它们能够有效地利用海底沉积物中的营养物质，并促进海洋生态系统内的食物循环。
