二氧化碳引起的海洋酸化對萊式擬烏賊生理及腸胃道微生物群的影響

Abstract

自工業革命之後，人類排放過多的二氧化碳到大氣中，使部分二氧化碳溶入海水中，並造成海水的酸鹼值逐漸下降。過去的研究指出：海洋酸化會造成海洋動物的消化能力下降以及體內的微生物組成改變。腸胃道微生物群的是一群生活在動物的腸胃道中的細菌，這些細菌對宿主的神經、消化和免疫系統有著巨大的影響。然而，相關的研究在頭足類中所知甚少。本研究運用萊式擬烏賊(Sepioteuthis lessoniana)，探討其長期於高碳酸環境中，其消化生理與腸胃道微生物群是否會改變。本研究運用剛孵化的萊式擬烏賊，分別飼養於正常海水 (控制組，pH ~ 8.1) 與高碳酸 (酸化組，pH ~ 7.8) 的海水中三個月。本研究發現相較於控制組，酸化組的萊式擬烏賊血液樣本中，會累積較高濃度的碳酸氫根離子；而在消化生理方面，海洋酸化會顯著提升萊式擬烏賊的澱粉酶、胰蛋白酶以及酯酶的活性。此外，本研究運用一種較傳統短片段定序更為精準的合成長片段 (SLR) 定序 LoopSeq™ 技術，並進一步在 Illumina NovaSeq 平臺上解析細菌的 16S rRNA，以研究萊式擬烏賊的腸胃道微生物群。根據微生物群落結構以及螢光原位雜合 (FISH) 解析得知：黴漿菌 (Mycoplasma) 是盲腸中最主要的屬，而弧菌 (Vibrio) 是腸道中最主要的屬。此外，跟據主座標散點圖 (PCoA) 以及置换多元方差分析 (PERMANOVA) 顯示：控制組和酸化組樣本間的微生物群在盲腸與腸道均沒有成分差異。Alpha多樣性分析顯示酸化組的盲腸微生物群的豐富度與多樣性，與在控制組相較產生明顯的差異，但在腸道中並無觀察到此差異。本研究首次深入解析萊式擬烏賊的腸道微生物群，並進一步探討海洋酸化對萊式擬烏賊消化生理功能和腸道微生物群的組成變化。研究結果顯示：萊式擬烏賊可能可以藉由有效調節其生理功能，以及維持腸胃道微生物群的穩定，以適應海洋酸化現象。

After the industrial revolution, the partial pressure of CO2 in the ocean increased from 280 atm to 400 atm, causing ocean acidification (OA). Ocean acidification has been shown to alter the digestion and composition of the microbial communities associated with marine animals. Gut microbes are a group of bacteria that colonize the digestive tracts of animals. Microbes in the gut may also play a crucial role in the nervous, digestive, and immune systems of the host; nevertheless, the related research on cephalopods is still limited. Under control (pH = 8.1) and OA (pH = 7.8) conditions, this study used the bigfin reef squid (Sepioteuthis lessoniana) to estimate host physiology and digestive tract microbial community. There was evidence that ocean acidification can result in bicarbonate accumulation in the blood of OA squids than in control ones. The enzymatic activities of amylase, trypsin, and lipase were higher in the OA group than in the control counterpart. Additionally, LoopSeqTM, a synthetic long-read (SLR) sequencing technology, was applied to generate highly accurate long reads of bacterial 16S rRNA gene, and this was further performed on an Illumina NovaSeq platform. The microbial community structure and fluorescence in situ hybridization indicate that Mycoplasma is the most dominant genus in the caecum, while Vibrio is the most dominant genus in the intestine. The principal coordinate scatter plot (PCoA) and the permutational multivariate analysis of variance (PERMANOVA) indicate no differences in microbial communities between the control and OA samples in both caecum and intestine. Alpha diversity showed that the caecum microbiota features under OA conditions differed significantly from those in the control group, but the difference could not be observed in the intestine. The present study is the first to examine the gut microbiota of bigfin reef squids and further estimate the possible impacts of ocean acidification on the gut microbiota, which could be important for bigfin reef squids to overcome the challenges induced by ocean acidification.