Use of palmitoleic acid and its oxidation products for monitoring the degradation of ice algae in Arctic waters and bottom sediments

Abstract

Degradation of palmitoleic acid (C 16:1x7), the main fatty acid component of sea ice-associated (sympagic) diatoms, was monitored in Arctic sea ice at the beginning of ice melting and in the underlying sinking particles and superficial bottom sediments. In sea ice, degradation of sympagic algae involved biotic oxidation induced by 10S-DOX-like lipoxygenase of unknown salinity-stressed attached bacteria, while photo-and autoxidation were limited. In the water column, strong hydratase and Z/E isomerase activity were observed. Hydration of unsaturated fatty acids seems to be a detoxification strategy, which is essential for bacterial survival when associated with free fatty acid-rich environments such as ice algae. In contrast, Z/E isomerisation of palmitoleic acid was attributed to the release of Fe 2+ ions during radicalinduced damage of the active site of the bacterial 10S-DOX-like lipoxygenase and Z/E isomerases. Due to the poor physiological state of their attached bacteria resulting from salinity stress in brine channels or toxicity of free ice algae fatty acids, sympagic algae appeared to be only very weakly biotically degraded within the water column. In bottom sediments, free radicals resulting from 10S-DOX-like lipoxygenase activity induced a strong autoxidation of the ice algal material. The presence in bottom sediments of a significant proportion of oxidation products resulting from 10S-DOX-like lipoxygenase activity attested to the strong contribution of sea ice-derived OM released during the early stages of ice melt prior to deposition in the sediments. However, on the basis of the highest fatty acid photooxidation state observed in these sediments, an additional contribution of highly photooxidized material (ice algal material released at the end of ice melting or open water phytoplankton) seems likely. The degradation of hydroperoxides, resulting from biotic and abiotic degradation of palmitoleic acid, appeared to involve: (i) homolytic cleavage of the peroxyl group affording the corresponding hydroxy-and oxoacids, (ii) reduction to the corresponding hydroxyacids by peroxygenases, (iii) heterolytic proton-catalysed cleavage and (iv) conversion to allylic 1,4-diols by diol synthases and hydroperoxide isomerases.

Seasonal monitoring of lipid degradation processes in the western English Channel links bacterial 10S-DOX enzyme activity to free fatty acid production by phytoplankton

“…6) can thus be attributed to the involvement of a specific biotic oxidation process. A similar dominance of this isomer among palmitoleic acid (22) oxidation products was observed previously in sea ice and in sinking particles in the Canadian Arctic (Amiraux et al, 2017;Rontani et al, 2018), and also in estuaries of diverse latitudes (Galeron et al, 2018). Its occurrence has previously been attributed to the involvement of specific bacterial dioxygenase activity and to a 10S-DOX enzyme, in particular.…”

“…The role played by autoxidation, photooxidation and 10S-DOX oxidation in the degradation of palmitoleic acid was estimated based on the profiles of isomeric allylic hydroxyacids obtained after NaBH4-reduction as described previously by Rontani et al (2018).…”

“…A focus of the study was the action of a particular bacterial enzyme (10S-DOX), which was previously observed in Arctic sea ice and sinking particles (Amiraux et al, 2017;Rontani et al, 2018), and in estuaries of diverse latitudes (Galeron et al, 2018); however, the role of this enzyme in the environment has hitherto remained unclear. Here, we hypothesised that this enzyme could be employed by bacteria to detoxify free fatty acids released by wounded diatoms, perhaps as a result of increased copepod activity (i.e.…”

Ionic Liquid–Ultrasound-Based Extraction of Biflavonoids from Selaginella helvetica and Investigation of Their Antioxidant Activity

“…Fe 2+ reacted with ferric trichloride and produced Prussian blue with a maximum absorbance at 700 nm. Based on the principle, if the absorbance measured of antioxygen was stronger, its reducing capacity was higher [39,40]. Figure 9C showed clearly that the reducing power of TBFE, quercetin (QUE), and ascorbic acid (Vc) increased markedly with the variation of sample concentration.…”

Viability and stress state of bacteria associated with primary production or zooplankton-derived suspended particulate matter in summer along a transect in Baffin Bay (Arctic Ocean)

“…It is well known that the uppermost section of the ice experiences the most drastic changes in brine salinity (Ewert and Deming, 2013). As a consequence, bacteria attached to sympagic algae in the bottommost ice are generally not highly affected by osmotic stress (Rontani et al, 2018;Amiraux et al, 2021a). The high trans/cis ratios of hexadec-11-enoic and vaccenic acids measured in the bottommost 3 cm of ice of St 409 and St 413 (Figs.…”