Specificity of Lipoxygenase Pathways Supports Species Delineation in the Marine Diatom Genus Pseudo-nitzschia

Abstract

Oxylipins are low-molecular weight secondary metabolites derived from the incorporation of oxygen into the carbon chains of polyunsaturated fatty acids (PUFAs). Oxylipins are produced in many prokaryotic and eukaryotic lineages where they are involved in a broad spectrum of actions spanning from stress and defense responses, regulation of growth and development, signaling, and innate immunity. We explored the diversity in oxylipin patterns in the marine planktonic diatom Pseudo-nitzschia. This genus includes several species only distinguishable with the aid of molecular markers. Oxylipin profiles of cultured strains were obtained by reverse phase column on a liquid chromatograph equipped with UV photodiode detector and q-ToF mass spectrometer. Lipoxygenase compounds were mapped on phylogenies of the genus Pseudo-nitzschia inferred from the nuclear encoded hyper-variable region of the LSU rDNA and the plastid encoded rbcL. Results showed that the genus Pseudo-nitzschia exhibits a rich and varied lipoxygenase metabolism of eicosapentaenoic acid (EPA), with a high level of specificity for oxylipin markers that generally corroborated the genotypic delineation, even among genetically closely related cryptic species. These results suggest that oxylipin profiles constitute additional identification tools for Pseudo-nitzschia species providing a functional support to species delineation obtained with molecular markers and morphological traits. The exploration of the diversity, patterns and plasticity of oxylipin production across diatom species and genera will also provide insights on the ecological functions of these secondary metabolites and on the selective pressures driving their diversification.

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

“…In fact, major products of C. closterium and C. scutellum derive from EPA by 15-LOX. This metabolism is common to many diatoms [23,26,34,36] and the resulting oxylipins were linked to the toxic activity on egg production and hatching success of the copepod Temora stylifera [42]. The enzyme prefers EPA as a primary substrate but it is possible that it can recognize also DHA with addition of molecular oxygen at C17 [38].…”

“…In analogy with planktonic species [23,25,[36][37][38][39], results on C. closterium, N. shiloi and C. scutellum revealed characteristic presence of hydroxy fatty acids (m/z 355, λ max = 234 nm, 11-HEPE and 15-HEPE) and epoxyalcohol fatty acids (m/z 371, 14,13-EHETE) of eicosa-5Z,8Z,11Z,14Z,17Z-pentaenoic acid (EPA, C20:5 ω3) even if the three species displayed different composition and levels of these compounds (Figure 1).…”

Time series and beyond: multifaceted plankton research at a marine Mediterranean LTER site

“…5d) would have hardly been attributed to a genus that is mainly identified by its conspicuous colonial stages (Zingone et al 1999a). Successfully, taxonomic research at LTER-MC has retained a traditional morphological approach at the same time as embracing different aspects of the species identity, such as phylogeny (Kooistra et al 2010, Gaonkar et al 2018, life cycles (Levialdi Ghiron et al 2008, Amato et al 2005, D'Alelio et al 2009b, mating compatibility with closely related species (Amato et al 2007, D'Alelio et al 2009a, biochemistry (Lamari et al 2013, Nanjappa et al 2014b, physiology and metabolomics (Degerlund et al 2012, feeding strategies (Modigh andFranzè 2009, Mahadik 2014), behavior (Bianco et al 2013, Mahadik et al 2017 as well as ecological aspects like species diversity during blooms (Orsini et al 2004) and phenology (Cerino et al 2005, D'Alelio et al 2010. It was precisely the latter trait, which can only be inferred from long-term observations, that draw attention to certain taxa, e.g., 'Skeletonema costatum (Greville) Cleve' showing different seasonality between the Tyrrhenian and Adriatic seas, or 'Leptocylindrus danicus Cleve' occurring all year round in the GoN.…”

Determination of Lipid Hydroperoxides in Marine Diatoms by the FOX2 Assay

“…Recent studies have highlighted differences in the oxylipin metabolism at the species and even clone level in diatoms [ 12 , 13 ], resulting in the production of several distinct end-metabolites. In certain diatom species, the chemical profiles of oxylipins corroborate the genotypic delineation, even among genetically closely-related cryptic species [ 14 ]. This suggests that oxylipin profiles may constitute an additional taxonomic identification tool, providing a functional support to species delineation obtained by molecular markers and morphological traits [ 14 ].…”