UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia.
School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia.
ISME J. 2020 Nov;14(11):2901-2905. doi: 10.1038/s41396-020-00771-3. Epub 2020 Sep 14.
Seagrasses and lucinid bivalves inhabit highly reduced sediments with elevated sulphide concentrations. Lucinids house symbiotic bacteria (Ca. Thiodiazotropha) capable of oxidising sediment sulphide, and their presence in sediments has been proposed to promote seagrass growth by decreasing otherwise phytotoxic sulphide levels. However, vast and productive seagrass meadows are present in ecosystems where lucinids do not occur. Hence, we hypothesised that seagrasses themselves host these sulphur-oxidising Ca. Thiodiazotropha that could aid their survival when lucinids are absent. We analysed newly generated and publicly available 16S rRNA gene sequences from seagrass roots and sediments across 14 seagrass species and 10 countries and found that persistent and colonising seagrasses across the world harbour sulphur-oxidising Ca. Thiodiazotropha, regardless of the presence of lucinids. We used fluorescence in situ hybridisation to visually confirm the presence of Ca. Thiodiazotropha on roots of Halophila ovalis, a colonising seagrass species with wide geographical, water depth range, and sedimentary sulphide concentrations. We provide the first evidence that Ca. Thiodiazotropha are commonly present on seagrass roots, providing another mechanism for seagrasses to alleviate sulphide stress globally.
海草和珠蚌栖息在高度还原、硫化物浓度升高的沉积物中。珠蚌体内共生着能够氧化沉积物中硫化物的细菌（Ca. Thiodiazotropha），其存在被认为可以通过降低原本对植物有毒的硫化物水平来促进海草的生长。然而，在没有珠蚌的生态系统中，也存在着广阔而多产的海草床。因此，我们假设海草本身就拥有这些能够帮助它们在没有珠蚌时生存的硫氧化 Ca. Thiodiazotropha。我们分析了来自 14 种海草和 10 个国家的新生成的、公开可用的 16S rRNA 基因序列，发现无论是否存在珠蚌，世界范围内的持久性和定殖性海草都含有硫氧化 Ca. Thiodiazotropha。我们使用荧光原位杂交技术（Fluorescence in situ Hybridization，FISH）在定殖性海草 Halophila ovalis 的根部上直观地证实了 Ca. Thiodiazotropha 的存在，Halophila ovalis 是一种具有广泛地理分布、水深范围和沉积物硫化物浓度的海草物种。这为 Ca. Thiodiazotropha 普遍存在于海草根部提供了第一个证据，为海草在全球范围内缓解硫化物胁迫提供了另一种机制。
