Metabolite profiling of the benthic diatom Cocconeis scutellum by GC-MS

Abstract

Cocconeis scutellum is a benthic diatom producing one or more compounds responsible for the early programmed cell death (apoptosis) of the male gonad and the androgenic gland of the protandric shrimp Hippolyte inermis Leach. The metabolite composition of both the ether and butanol extracts was studied by gas chromatography-mass spectrometry (GC-MS) in both electron impact (EI) and chemical ionization (CI) mode. The compounds were identified as trimethylsilyl (TMSi) derivatives. The structure of the fatty acids (FA) was confirmed after conversion to their methyl esters. The ether fraction of C. scutellum contained FA (76%), of which 30% were saturated (SFA), 24% monounsaturated (MUFA) and 22% polyunsaturated (PUFA). Mono-(8%) and diglycerides (3%) as well as sterols (5%) and isoprenoid compounds (4%) were also found in this fraction. The butanol extract consisted of FA (45%), carbohydrates (25%), amino acids and N-containing metabolites (10%), fatty alcohols (9%), glycerides (4%) and organic acids (3%). In the literature, many reports deal with the chemistry and the chemical ecology of planktonic diatoms; contrastingly, benthic species are still less studied, especially with respect to their chemical composition, due to their difficult cultivation. Hence, our investigation represents a preliminary approach to clarify on chemical bases the ecological role of Cocconeis on decapods in the marine benthos, as well as a description of the metabolic pattern of this benthic diatom.

Apoptotic activity of the marine diatomCocconeis scutellumand eicosapentaenoic acid in BT20 cells

“…As previously reported (Nappo et al, 2009), the chemical composition of C. scutellum diatoms consisted mainly of FAs, sterols and glycerides, and low amounts of N-containing metabolites, disaccharides and isoprenoid compounds. The separation of the microalgal metabolites into a diethyl ether extract, composed by less polar compounds, and a butanol extract, consisting in more polar compounds, allowed us to obtain a preliminary assignment of the apoptotic activity among the most apolar compounds.…”

“…Among the FAs found in fraction 3 (Table 1), only EPA (C20:5) has been reported to possess bioactivity (Chajès et al, 1995). Thus, we tested the apoptotic activity of EPA along with that of arachidonic acid (AA, C20:4), another PUFA detected in the diethyl ether extract (Nappo et al, 2009). The viable and apoptotic BT20 cells were 34.1% and 45.3%, respectively, at 7 μg/well of EPA.…”

“…In fact, affecting the sex reversal of this shrimp by fasting the disruption of the androgenic gland, these diatoms guarantee an adequate number of females for the autumn mating period. It has been demonstrated that aldehydes are not involved in the diatom-induced apoptosis (Zupo et al, 2007;Nappo et al, 2009), but it cannot be excluded that other kinds of oxylipins could be responsible for the programmed cell death. Further investigations are required in order to clarify this point.…”

“…Aliquots of fractions 1-3 (ca. 2-3 mg) were silylated, transmethylated and analyzed by gas chromatography-mass spectrometry (GC-MS) as previously described (Nappo et al, 2009). …”

Odour compounds of the diatom Cocconeis scutellum: effects on benthic herbivores living on Posidonia oceanica

“…Mar Ecol Prog Ser 400: [63][64][65][66][67][68][69][70][71][72][73] 2010 compound (whose structure has not yet been identified; Nappo et al 2009) present in these diatoms acts as a spring signal for the production of young females, probably due to a long co-evolutionary process .…”