Zvi-Kedem Tal, Vintila Simina, Kleiner Manuel, Tchernov Dan, Rubin-Blum Maxim
Biology Department, National Institute of Oceanography, Israel Oceanographic and Limnological Research (IOLR), Haifa, 3108000, Israel.
Morris Kahn Marine Research Station, Department of Marine Biology, Leon H. Charney School of Marine Sciences, University of Haifa, Haifa, 3498838, Israel.
ISME Commun. 2023 May 20;3(1):48. doi: 10.1038/s43705-023-00254-4.
Bathymodioline mussels rely on thiotrophic and/or methanotrophic chemosynthetic symbionts for nutrition, yet, secondary heterotrophic symbionts are often present and play an unknown role in the fitness of the organism. The bathymodioline Idas mussels that thrive in gas seeps and on sunken wood in the Mediterranean Sea and the Atlantic Ocean, host at least six symbiont lineages that often co-occur. These lineages include the primary symbionts chemosynthetic methane- and sulfur-oxidizing gammaproteobacteria, and the secondary symbionts, Methylophagaceae, Nitrincolaceae and Flavobacteriaceae, whose physiology and metabolism are obscure. Little is known about if and how these symbionts interact or exchange metabolites. Here we curated metagenome-assembled genomes of Idas modiolaeformis symbionts and used genome-centered metatranscriptomics and metaproteomics to assess key symbiont functions. The Methylophagaceae symbiont is a methylotrophic autotroph, as it encoded and expressed the ribulose monophosphate and Calvin-Benson-Bassham cycle enzymes, particularly RuBisCO. The Nitrincolaceae ASP10-02a symbiont likely fuels its metabolism with nitrogen-rich macromolecules and may provide the holobiont with vitamin B12. The Urechidicola (Flavobacteriaceae) symbionts likely degrade glycans and may remove NO. Our findings indicate that these flexible associations allow for expanding the range of substrates and environmental niches, via new metabolic functions and handoffs.
深海贻贝依靠硫营养型和/或甲烷营养型化学合成共生体获取营养，然而，次级异养共生体也常常存在，并且在生物体的健康状况中发挥着未知的作用。在地中海和大西洋的天然气渗漏区及沉没木材上繁衍生息的深海贻贝伊达斯贻贝，宿主至少六种共生体谱系，这些谱系常常同时出现。这些谱系包括初级共生体化学合成甲烷和硫的氧化γ-变形菌，以及次级共生体甲基噬菌科、硝化菌科和黄杆菌科，它们的生理和代谢情况尚不清楚。关于这些共生体是否以及如何相互作用或交换代谢产物，人们知之甚少。在这里，我们精心挑选了伊达斯贻贝共生体的宏基因组组装基因组，并使用以基因组为中心的宏转录组学和宏蛋白质组学来评估关键的共生体功能。甲基噬菌科共生体是一种甲基营养型自养生物，因为它编码并表达了磷酸核糖单磷酸和卡尔文-本森-巴斯姆循环酶，尤其是核酮糖-1,5-二磷酸羧化酶/加氧酶。硝化菌科ASP10-02a共生体可能利用富含氮的大分子为其代谢提供能量，并可能为共生体提供维生素B12。脲栖菌属（黄杆菌科）共生体可能降解聚糖并可能去除一氧化氮。我们的研究结果表明，这些灵活的共生关系通过新的代谢功能和物质传递，使得底物范围和环境生态位得以扩展。
