Sharma Diksha, Menon Vignesh Gokuladas, Desai Manasi, Niu Danielle, Bates Eleanor, Kandel Annie, Zinser Erik R, Fields David M, O'Toole George A, Sharma Mukul
Department of Earth Sciences, Dartmouth College, New Hampshire, USA.
Laboratoire d'Océanographie et du Climat, CNRS-IRD MNHN- Sorbonne University, Paris, France.
Sci Rep. 2024 Dec 10;14(1):28863. doi: 10.1038/s41598-024-79912-z.
Marine microorganisms play a critical role in regulating atmospheric CO concentration via the biological carbon pump. Deposition of continental mineral dust on the sea surface increases carbon sequestration but the interaction between minerals and marine microorganisms is not well understood. We discovered that the interaction of clay minerals with dissolved organic matter and a γ-proteobacterium in seawater increases Transparent Exopolymer Particle (TEP) concentration, leading to organoclay floc formation. To explore this observation further, we conducted a microcosm experiment using surface seawater collected from the Spring 2023 phytoplankton bloom in the Gulf of Maine. Unfiltered (natural community) and filtered (200 μm and 3 μm) seawater was sprayed with clay (20 mg L and 60 mg L) and incubated. All clay treatments led to a tenfold increase in TEP concentration. 16S rRNA gene amplicon sequence analyses of seawater and settled organoclay flocs showed the dominance of α-proteobacteria, γ-proteobacteria, and Bacteroidota. The initial seawater phytoplankton community was dominated by dinoflagellates followed by a haptophyte (Phaeocystis sp.) and diatoms. Following clay addition, dinoflagellate cell abundance declined sharply while diatom cell abundance increased. By analyzing organoclay flocs for 18S rRNA we confirmed that dinoflagellates were removed in the flocs. The clay amendment removed as much as 50% of phytoplankton organic carbon. We then explored the fate of organoclay flocs at the next trophic level by feeding clay and phytoplankton (Rhodomonas salina) to Calanus finmarchicus. The copepod ingested R. salina and organoclay flocs and egested denser fecal pellets with 1.8- to 3.6- fold higher sinking velocity compared to controls. Fecal pellet density enhancement could facilitate carbon sequestration through zooplankton diel vertical migration. These findings provide insights into how atmospheric dust-derived clay minerals interact with marine microorganisms to enhance the biological carbon pump, facilitating the burial of organic carbon at depths where it is less likely to exchange with the atmosphere.
海洋微生物在通过生物碳泵调节大气二氧化碳浓度方面发挥着关键作用。大陆矿物尘埃在海面的沉积增加了碳固存，但矿物与海洋微生物之间的相互作用尚未得到充分理解。我们发现，粘土矿物与海水中溶解的有机物和一种γ-变形菌的相互作用会增加透明胞外聚合物颗粒（TEP）的浓度，导致有机粘土絮凝物的形成。为了进一步探究这一现象，我们使用从2023年春季缅因湾浮游植物大量繁殖时采集的表层海水进行了一项微观实验。向未过滤（自然群落）和过滤（200微米和3微米）的海水中喷洒粘土（20毫克/升和60毫克/升）并进行培养。所有粘土处理都使TEP浓度增加了十倍。对海水和沉降的有机粘土絮凝物进行的16S rRNA基因扩增子序列分析表明，α-变形菌、γ-变形菌和拟杆菌门占主导地位。初始海水浮游植物群落以甲藻为主，其次是一种定鞭藻（棕囊藻属）和硅藻。添加粘土后，甲藻细胞丰度急剧下降，而硅藻细胞丰度增加。通过分析有机粘土絮凝物中的18S rRNA，我们证实甲藻在絮凝物中被去除。粘土改良去除了多达50%的浮游植物有机碳。然后，我们通过将粘土和浮游植物（盐生红藻）投喂给细基江蓠繁枝变型，探究了有机粘土絮凝物在下一个营养级的命运。与对照组相比，桡足类摄取了盐生红藻和有机粘土絮凝物，并排出了下沉速度高1.8至3.6倍的更密集粪便颗粒。粪便颗粒密度的增加可能通过浮游动物的昼夜垂直迁移促进碳固存。这些发现为大气尘埃衍生的粘土矿物如何与海洋微生物相互作用以增强生物碳泵提供了见解，有助于将有机碳埋藏在不太可能与大气交换的深度。
