This study investigated the fatty acids (FA) profile of 54 actinomycete strains isolated from marine sediments collected off the Portugal continental coast, specifically from the Estremadura Spur pockmarks field, by GC/MS. Fatty acid methyl esters (FAMEs) were prepared from the ethyl acetate lipidic extracts of these strains and analyzed by gas chromatography–mass spectrometry (GC/MS), with FA identification performed using the NIST library. The identified FAs varied from C12:0 to C20:0, where 32 distinct FAs were identified, including 7 branched-chain fatty acids (BCFAs), 9 odd-chain fatty acids (OCFAs), 8 monounsaturated fatty acids (MUFAs), 6 saturated fatty acids (SFAs), 1 polyunsaturated fatty acid (PUFA), and 1 cyclic chain fatty acid (CCFA). The average expressed content was BCFA (47.54%), MUFA (28.49%), OCFA (26.93%), and SFA (22.16%), of which i-C16:0, C18:1ω9, and C16:0 were predominant, while PUFA (3.58%) and CCFA (0.41%) were identified as minor components. The identified BCFA were i-C16:0, a-C15:0, i-C15:0, i-C15:1ω6, a-C16:0, a-C14:0, and i-C17:0, which include combined branching and unsaturation and branching and odd. SFAs were present in all species, with C16:0 and C18:0 being the most representative. Rare OCFAs C19:1ω9, C17:1ω7, C15:0, and C17:0 were expressed. PUFA C18:1ω9 was detected; within this class, omega families ω9, ω7, ω6, and ω5 were identified, and no ω3 was detected. The only CCFA was benzene-butanoic acid (benzene-C4:0). These findings highlight the metabolic versatility of actinomycetes, providing valuable insights into microbial chemotaxonomy and offering promising biochemical leads for the development of biofuel, nutraceutical, and antifungal agents. Furthermore, these results underline the diversity and biotechnological potential of FAs in actinomycetes, uncovering their potential to be used as microbial cell factories, and paving the way for innovations in biofuels, pharmaceuticals, and eco-friendly industrial products.

Monitoring trace metals in commercially important fish species provides an early warning of anthropogenic contamination and potential risk to consumers. This study semi-quantified and quantified essential, non-essential, and toxic elements in the muscle of wild meagre (Argyrosomus regius) captured in the Tagus estuary (Portugal), which is used as a nursery and spawning aggregation area. Dry muscle was microwave-digested and analyzed using inductively coupled plasma–optical emission spectroscopy. Semi-quantified screening detected Al, B, Ca, Fe, K, Mg, Na, P, S, Si, Sr, and Ti, and eight elements were determined using multielement calibration (As, Cr, Cu, Hg, Mn, Ni, Se, and Zn); Cd, Pb (toxic elements), Co, and Mo were not detected in this study. Arsenic was detected in all individuals, with a minimum value of 0.348 mg/kg wet weight. A mercury level above the European Commission regulatory limit (0.5 mg/kg wet weight) was only detected in one individual, corresponding to 2% of the samples. Although other metals remain well below regulatory limits, continued biomonitoring is recommended to track temporal trends and safeguard seafood safety in transitional coastal systems, which is important for commercially relevant fish species.

The fatty acid signature and temperature marker FAs of total polar lipids (PLs) and of the two main phospholipid classes, i.e., phosphatidylcholine (PC) and phosphatidylethanolamine (PE), present in the cardiac muscle of wild meagre (Argyrosomus regius) caught in the Tagus estuary (Portugal) were tested as habitat biomarkers to assess whether there were differences associated with the life cycle stage (i.e., juveniles vs. adults). Dried cardiac muscle was extracted using accelerated solvent extraction (ASE), fractionated by solid-phase extraction (SPE) and high-performance thin-layer chromatography (HPTLC), and analyzed by gas chromatography with flame ionization detection (GC-FID). A clear distinction was found between juveniles and adults in terms of cardiac PL fatty acid profile, temperature marker fatty acids, and in the PC/PE ratio. All differences were statistically significant, reflecting differences in thermal adaptation and thus indicating spatial segregation between juveniles and adults within the estuarine environment. Our findings demonstrated a cardiac fatty acid signature indicative of adaptation to distinct habitats and thermal regimes, manifested through alterations in either the PL profile or the restructuring of the PC and PE classes. According to our results, adult individuals stay in a cooler/deep zone and with high influence of the sea within the estuarine systems (mouth of the estuary), and the juveniles in warmer/shallower and less sea-influenced zones.