期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：46
页码：13191-13196
DOI：10.1073/pnas.1611666113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceTrichodesmium spp. are globally significant contributors of new nitrogen to the surface ocean. Marine organisms must accumulate compatible solutes in their cells, counteracting the high exterior osmotic pressure. However, Trichodesmium does not possess any known genes for the synthesis of compatible solutes, making its proliferation in the high-salinity environment enigmatic. We demonstrate that Trichodesmium cultures in the laboratory as well as natural populations in the ocean synthesize homoserine betaine, previously unknown as a compatible solute, and elucidated the biosynthetic pathway. The high intracellular concentrations will lead to a major injection of this organic compound into the oligotrophic ocean, when natural Trichodesmium blooms lyse. Such sudden releases of homoserine betaine could impact the biogeochemical cycling of carbon and nitrogen. The oceanic N2-fixing cyanobacterium Trichodesmium spp. form extensive surface blooms and contribute significantly to marine carbon and nitrogen cycles in the oligotrophic subtropical and tropical oceans. Trichodesmium grows in salinities from 27 to 43 parts per thousand (ppt), yet its salt acclimation strategy remains enigmatic because the genome of Trichodesmium erythraeum strain IMS101 lacks all genes for the biosynthesis of any known compatible solute. Using NMR and liquid chromatography coupled to mass spectroscopy, we identified the main compatible solute in T. erythraeum strain IMS101 as the quaternary ammonium compound N,N,N-trimethyl homoserine (or homoserine betaine) and elucidated its biosynthetic pathway. The identification of this compatible solute explains how Trichodesmium spp. can thrive in the marine system at varying salinities and provides further insight into the diversity of microbial salt acclimation.
