平端深海偏顶蛤(Gigantidas platifrons)实验室蓄养过程鳃部含菌上皮细胞超微结构动态变化研究

ULTRASTRUCTURE OF BACTERIOCYTES IN GILLS OF GIGANTIDAS PLATIFRONS IN LONG-TERM CULTIVATION

平端深海偏顶蛤(Gigantidasplatifrons)是南海台西南冷泉区的典型优势物种,鳃丝上皮细胞内共生大量甲烷氧化菌,通过甲烷有氧氧化合成有机物为共生体系提供物质能量,是平端深海偏顶蛤赖以生存的重要能量来源器官,溶酶体在共生体系的营养互作和稳态维持中可能发挥重要作用,本研究使用电镜技术观测了常压培养过程中(0d,30d,90d)平端深海偏顶蛤共生体系中共生菌和溶酶体的动态变化,通过鳃上皮含菌细胞超显微结构的变化研究常压培养对深海共生体系的影响,并探讨溶酶体在宿主-共生菌营养传递和共生菌群稳态维持中的关键作用。研究发现,在原位状态样品中(0d)共生菌和溶酶体呈极化分布,细胞结构完整清晰;蓄养30d后,含菌细胞出现明显破碎,共生菌数量大幅降低,溶酶体数量、范围和消化程度大幅增加,对细胞顶端的甲烷氧化菌进行分解;而90d后,共生菌在溶酶体的作用下消失殆尽,鳃部有明显细胞脱落后留下的坑洞,细胞呈现空泡状,无法明确区分各种细胞组分。上述结果展示了长期常压蓄养过程中鳃上皮含菌细胞中溶酶体与甲烷氧化菌的动态变化,推测当共生菌丢失后溶酶体也同步降低活跃度,平端深海偏顶蛤在共生互作中通过溶酶体主导消化和调控共生菌。

Gigantidas platifrons is a dominant species in cold seep in the South China Sea, northwest to Taiwan, China. The epithelial cells of the gills are filled with a large number of methane oxidizing bacteria(MOB) for providing energy to the hosts. Lysosomes may play an important role in the nutritional interaction and maintenance of homeostasis of the symbiotic system. To unveil how the symbionts change during the incubation and the roles of lysosome in the symbiosis, the ultrastructure of the bacteriocytes in G. platifrons was studied in electron microscopy and compared after being incubated in normal pressure for 30 and 90 days. Polarized distributions of the MOB and lysosome in the bacteriocytes were observed in the in-situ specimens on Day 0 immediately sampled. The symbionts were concentrated at water-cell interfaces and lysosomes were present near the basilar membrane. On Day 30 of the incubation, the integrity and abundance of the symbionts in the bacteriocytes decreased. In contrast, the quantity and the digestion level of the secondary lysosomes increased significantly. On Day 90 of the incubation, the MOB disappeared owing to the digestion of lysosomes. Obvious pits were observed on the gill surface, which might be due to the loss of bacteriocytes. The gill epithelia were vacuolated because the cellular organelles could not be distinguished. Based on the dynamic changes of symbiont and the lysosomes during the long-term incubation, we proposed that the lysosomes could function to digest symbionts and eliminate the senile or premortal symbionts actively. This conclusion was further supported by the suppressed lysosomes after the loss of the symbionts.