Abstract
Sponges produce distinct fatty acids (FAs) that (potentially) can be used as chemotaxonomic and ecological biomarkers to study endosymbiont-host interactions and the functional ecology of sponges. Here, we present FA profiles of five common habitat-building deep-sea sponges (class Demospongiae, order Tetractinellida), which are classified as high microbial abundance (HMA) species. Geodia hentscheli, G. parva, G. atlantica, G. barretti, and Stelletta rhaphidiophora were collected from boreal and Arctic sponge grounds in the North-Atlantic Ocean. Bacterial FAs dominated in all five species and particularly isomeric mixtures of mid-chain branched FAs (MBFAs, 8- and 9-Me-C16:0 and 10- and 11-Me-C18:0) were found in high abundance (together ≥ 20% of total FAs) aside more common bacterial markers. In addition, the sponges produced long-chain linear, mid- and a(i)-branched unsaturated FAs (LCFAs) with a chain length of 24‒28 C atoms and had predominantly the typical Δ5,9 unsaturation, although the Δ9,19 and (yet undescribed) Δ11,21 unsaturations were also identified. G. parva and S. rhaphidiophora each produced distinct LCFAs, while G. atlantica, G. barretti, and G. hentscheli produced similar LCFAs, but in different ratios. The different bacterial precursors varied in carbon isotopic composition (δ13C), with MBFAs being more enriched compared to other bacterial (linear and a(i)-branched) FAs. We propose biosynthetic pathways for different LCFAs from their bacterial precursors, that are consistent with small isotopic differences found in LCFAs. Indeed, FA profiles of deep-sea sponges can serve as chemotaxonomic markers and support the concept that sponges acquire building blocks from their endosymbiotic bacteria.
Highlights
MethodsSponge collectionCommon habitat-building sponges of class Demospongiae, order Tetractinellida, were collected in the North-Atlantic Ocean by remotely operated vehicle (ROV) and box cores during different scientific expeditions
Sponges are abundant inhabitants of most aquatic ecosystems including the deep-sea [1]
The PL derived fatty acids (FAs) (PLFA) profiles of PL resembled those of total lipid extract (TLE) and the majority of FA seemed to be present in PL (S1 Table, [38])
Summary
Sponge collectionCommon habitat-building sponges of class Demospongiae, order Tetractinellida, were collected in the North-Atlantic Ocean by remotely operated vehicle (ROV) and box cores during different scientific expeditions. G. atlantica (n = 2) specimens were collected on the Sula Reef between 266–295 m depth during an expedition in August 2017 with the Norwegian research vessel G.O. Sars (64 ̊42’N 7 ̊59’E). G. barretti (n = 6) individuals were obtained from the Barents Sea (70 ̊47N 18 ̊03’E) around 300 m water depth on a subsequent G.O. Sars expedition in August 2018 [28]. G. hentscheli (n = 3), G. parva (n = 3), and S. rhaphidiophora (n = 2) specimens were retrieved on an Arctic expedition with the German research vessel Polarstern (AWI Expedition PS101) in September–October 2016 at 690–1000 m depth from Langseth Ridge, located in the permanently ice-covered Central Arctic (from 87 ̊N, 62 ̊E to 85 ̊55’N 57 ̊ 45’E). The powdered subsamples of sponges from Schulz Bank and Barents Sea were mixed to obtain a species representative sample, while a subsample of the interior of sponges was analyzed in case of Langseth Ridge specimens.
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