Lipoxygenase Pathways in Diatoms: Occurrence and Correlation with Grazer Toxicity in Four Benthic Species

Abstract

Oxygenated derivatives of fatty acids, collectively called oxylipins, are a highly diverse family of lipoxygenase (LOX) products well described in planktonic diatoms. Here we report the first investigation of these molecules in four benthic diatoms, Cylindrotheca closterium, Nanofrustulum shiloi, Cocconeis scutellum, and Diploneis sp. isolated from the leaves of the seagrass Posidonia oceanica from the Gulf of Naples. Analysis by hyphenated MS techniques revealed that C. closterium, N. shiloi, and C. scutellum produce several polyunsaturated aldehydes (PUAs) and linear oxygenated fatty acids (LOFAs) related to the products of LOX pathways in planktonic species. Diploneis sp. also produced other unidentified fatty acid derivatives that are not related to LOX metabolism. The levels and composition of oxylipins in the benthic species match their negative effects on the reproductive success in the sea urchin Paracentrotus lividus. In agreement with this correlation, the most toxic species N. shiloi revealed the same LOX pathways of Skeletonema marinoi and Thalassiosira rotula, two bloom-forming planktonic diatoms that affect copepod reproduction. Overall, our data highlight for the first time a major role of oxylipins, namely LOFAs, as info-chemicals for benthic diatoms, and open new perspectives in the study of the structuring of benthic communities.

Multiple Roles of Diatom-Derived Oxylipins within Marine Environments and Their Potential Biotechnological Applications

“…De novo transcriptome approaches also revealed that benthic species affected several molecular pathways with very few common targets [ 75 , 77 ]. The highest activity detected in N. shiloi species may be explained by chemical analyses [ 22 ]. In fact, N. shiloi revealed a high content of both oxygenated fatty acids and PUAs, while C. closterium was less rich in oxylipins and produced mainly non-volatile oxygenated fatty acids.…”

“…In fact, N. shiloi revealed a high content of both oxygenated fatty acids and PUAs, while C. closterium was less rich in oxylipins and produced mainly non-volatile oxygenated fatty acids. Interestingly, Diploneis sp., inducing about 40% of malformed plutei, exhibited several unknown compounds, probably related to a LOX-independent fatty acids metabolism [ 22 ]. According to feeding experiments, in which no negative effects were detected [ 77 ], a total absence of oxylipins was found in C. scutellum [ 22 ].…”

“…Interestingly, Diploneis sp., inducing about 40% of malformed plutei, exhibited several unknown compounds, probably related to a LOX-independent fatty acids metabolism [ 22 ]. According to feeding experiments, in which no negative effects were detected [ 77 ], a total absence of oxylipins was found in C. scutellum [ 22 ]. This result supports those by Zupo et al [ 81 ] that post-larval feeding with C. scutellum induces only positive effects such as post-larvae settlement (about 63%) and survival.…”

“…The enzymatic cascade leading to oxylipin production involves lipoxygenase (LOX)/hydroperoxide lyase (HPL) enzymes, which convert polyunsaturated fatty acids (PUFAs) into fatty acid hydroperoxides that are, in turn, converted into a plethora of compounds through mechanisms that are still largely unknown [ 15 , 16 , 17 , 18 , 19 , 20 ]. Oxylipins are a large family of compounds comprising polyunsaturated aldehydes (PUAs), firstly identified from Thalassiosira rotula [ 7 ], and other fatty acid derivatives with hydroxy-, keto-, oxo- and hydroxy-epoxy units, generically named non-volatile oxylipins [ 21 ] and recently reported as linear oxygenated fatty acids [ 22 ]. Several studies have suggested that, in addition to PUAs and oxygenated fatty acids, fatty acid hydroperoxides can trigger impacts on marine biota because these primary LOX products are reactive oxygen species (ROS), inducing DNA and protein damage that contribute to cell ageing [ 19 ].…”

“…Chemical analyses of mono-algal cultures has revealed strictly LOX species-specificity [ 30 ], where the most common pathway shared by different genera of diatoms rely on a 15 S -LOX activity, and a minor group of oxylipins are the products of 5-LOX, 8-LOX, 9 S -LOX, 11-LOX, 12-LOX and 14-LOX [ 19 , 20 , 22 , 30 , 31 , 32 , 33 , 34 ] activity, depending on the specific regiochemistry of carbon oxidation. Oxylipin quantification and variation in time and space has been evaluated in field studies [ 35 , 36 , 37 , 38 , 39 , 40 , 41 ].…”