Fatty acids associated with the frustules of diatoms and their fate during degradation—A case study in Thalassiosira weissflogii

Abstract

12Diatoms are major actors in the export of organic carbon out of the euphotic zone. Yet, 13 the processes linking biogenic silica and carbon sedimentation fluxes to deep oceanic layers 14 remain unclear. Analysing organic fractions in biominerals is challenging because efficient 15 cleaning often led to structural alteration of organic molecules. Hence, although lipids are 16 widely used as biogeochemical markers in ocean flux study, few studies have dealt with the 17 lipids that are associated with frustules. In the present study, a protocol was set up to extract 18 and quantify the fatty acids associated to the frustule of the diatom species Thalassiosira 19 weissflogii. The protocol involves solvent extraction of diatom external lipids, followed by 20 clean frustule dissolution by 4% NaOH during 1h at 95°C and subsequent solvent re-21 extraction of frustule-associated lipids. Results confirmed that this protocol was efficient first, 22to isolate the frustule from the rest of the cellular organic carbon and second to extract and 23 quantify fatty acids (FA) associated to frustules of this species. FA composition of the 24 frustules was significantly different from that of the whole cells consisting primarily of 14:0, 25 34 Keywords: Frustule, Diatoms, Organic Carbon, Lipids, Carbon Export 35 36 Frustule isolation 132Pellet samples were resuspended in 40 ml milliQ water and were hot-sonicated at 70 133 °C for 5 min to fragment the cells (Fig. 1). Tubes were subsequently centrifuged at 5400 g for 134 40 min at 4 °C. The supernatants were removed, and this step was repeated once at lower 135

Diatom frustules as a biomaterial: effects of chemical treatment on organic material removal and mechanical properties in cleaned frustules from two Coscinodiscus species

“…After subtraction of the oxygen signal from SiO2 using an O:Si ratio of 2, we estimated a O:C-ratio of 1.5 ± 0.4 in the organic material associated with the frustules. The organic material could be carbohydrates [41] or lipids [46] , however, the high O:C ratio excludes lipids as a likely constituent in our study. Other elements may be used to identify the sources of auto fluorescence, but here the amounts of N, P and S were close to the detection limit (0.1 %) in un-cleaned frustules, hence proteins and nucleic acids were unlikely the major constituents of the organic material associated with the frustules.…”

Phosphorus limitation affects the molecular composition of Thalassiosira weissflogii leading to increased biogenic silica dissolution and high degradation rates of cellular carbohydrates

“…S2: FTIR spectra of the frustule in the "P-replete T. weissflogii" (red line) and in the "Pstress T. weissflogii" batch (blue line) at day 2 (T2) of degradation. Briefly, samples were collected after 2 days of degradation and frustules were extracted according Suroy et al (2014). The sample preparation and FTIR analysis were carried out as previously described in the legend of Fig.…”

The Effect of Essential Fatty Acids for the Somatic Growth in Nauplii of Calanus finmarchicus

“…adults feeding on detritus are scarce and the results are contradictory (Paffenhöfer and Strickland, 1970;Carlotti and Radach, 1996;Dilling et al, 1998). We therefore suggest that nauplii grazing selectively on phytoplankton and ciliates (Turner et al, 2001;Irigoien et al, 2003) might have experienced higher DHA-and EPAconcentrations in their actual food than what we measured in the seston samples, because dead matter is likely lower in these fatty acids than live plankton (Suroy et al, 2014).…”