Fatty acid (FA) analysis is a well- established tool for studying trophic interactions in marine habitats. However, its application to benthic food webs poses 2 particular challenges. First, unlike pelagic zooplankton, benthic con- sumers have access to different sizes and func- tional groups of primary producers and may con- sume a highly mixed diet. Classes of benthic primary producers are distinct in their overall FA composition, but most do not possess unique marker FAs that can be used to identify their con- tribution to higher trophic levels. Second, unlike mammalian predators, benthic invertebrates have the capacity to significantly modify their dietary FAs and thereby obscure markers for food sources. Controlled feeding studies have been used to dis- tinguish dietary tracer FAs from those that are modified by the consumer in several benthic invertebrates, but more such studies are needed. Despite these challenges, FAs have been used to study trophic structure in a variety of benthic habitats including the deep sea, polar regions, estuaries, and the rocky subtidal zone. However, the complexity of benthic food webs and lack of unique markers impose uncertainties in the inter- pretation of FA data from field studies. Multivari- ate analyses are necessary for analyzing FA datasets, although univariate tests can be useful for comparing levels of informative FAs among food sources and consumers. Combining FA analysis with other lines of evidence, such as sta- ble isotope analysis, offers a more reliable approach to examining trophic interactions in benthic systems.

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Fatty acids as dietary tracers in benthic food webs

Because of their characteristic living environments, marine organisms produce a variety of lipids. Fatty acids constitute the essential part of triglycerides and wax esters, which are the major components of fats and oils. Nevertheless, phospholipids and glycolipids have considerable importance and will be taken into account, especially the latter compounds that excite increasing interest regarding their promising biological activities. Thus, in addition to the major polyunsaturated fatty acids (PUFA) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, a great number of various fatty acids occur in marine organisms, e.g. saturated, mono- and diunsaturated, branched, halogenated, hydroxylated, methoxylated, non-methylene-interrupted. Various unprecedented chemical structures of fatty acids, and lipid-containing fatty acids, have recently been discovered, especially from the most primitive animals such as sponges and gorgonians. This review of marine lipidology deals with recent advances in the field of fatty acids since the end of the 1990s. Different approaches will be followed, mainly developing biomarkers of trophic chains in marine ecosystems and of chemotaxonomic interest, reporting new structures, especially those with biological activities or biosynthetic interest. An important part of this review will be devoted to the major PUFA, their relevance to health and nutrition, their biosynthesis, their sources (usual and promising) and market.

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Fatty acids from lipids of marine organisms: molecular biodiversity, roles as biomarkers, biologically active compounds, and economical aspects.

Recent advances in the biochemistry and molecular biology of fatty acyl desaturases.

/pdf/polyunsaturated-fatty-acids-in-marine-bacteria-a-dogma-1nsm3h1dpe.pdf

Polyunsaturated fatty acids in marine bacteria--a dogma rewritten.

Virtually all polyunsaturated fatty acids (PUFA) originate from primary producers but can be modified by bioconversions as they pass up the food chain in a process termed trophic upgrading. Therefore, although the main primary producers of PUFA in the marine environment are microalgae, higher trophic levels have metabolic pathways that can produce novel and unique PUFA. However, little is known about the pathways of PUFA biosynthesis and metabolism in the levels between primary producers and fish that are largely filled by invertebrates. It has become increasingly apparent that, in addition to trophic upgrading, de novo synthesis of PUFA is possible in some lower animals. The unequivocal identification of PUFA biosynthetic pathways in many invertebrates is complicated by the presence of other organisms within them. These organisms include bacteria and algae with PUFA biosynthesis pathways, and range from intestinal flora to symbiotic relationships that can involve PUFA translocation to host organisms. This emphasizes the importance of studying biosynthetic pathways at a molecular level, and the continual expansion of genomic resources and advances in molecular analysis is facilitating this. The present paper highlights recent research into the molecular and biochemical mechanisms of PUFA biosynthesis in marine invertebrates, particularly focusing on cephalopod molluscs.

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Biosynthesis of Polyunsaturated Fatty Acids in Marine Invertebrates: Recent Advances in Molecular Mechanisms

Bacteria producing the two long-chained polyunsaturated fatty acids eicosapentaenoic (20:5 n–3) and docosahexaenoic (22:6 n–3) acid, which principally have been associated with deep-sea environments, were found in the culturable flora of all species of a selection of 10 arctic and sub-arctic invertebrates and in one of four fish species. In total, 103 out of 330 strains which were tested carried this trait. Highest prevalences, i.e., more than 50% of total isolates were detected in two species of bivalves (Chlamys islandica and Astarte sp.) and in the amphipod Gammarus wilkitzkii. Standard taxonomic tests, supplemented with fatty-acid profile analysis, affiliated all polyunsaturated-fatty-acid producing strains either to the pseudomonad or vibrio main groups of marine bacteria.

High prevalence of polyunsaturated-fatty-acid producing bacteria in arctic invertebrates

Molecular-phylogenetic, structural and biochemical features of a cold-adapted, marine ichthyosporean near the animal-fungal divergence, described from in vitro cultures

The influence on fatty acid composition of growth medium composition and phase of growth during batch culture and of dilution rate and growth temperature during continuous culture was studied in the eicosapentaenoic-acid (20:5 n-3)-producing Vibrio CCUG 35308. In glucose-mineral medium, even-numbered normal fatty acyl residues, primarily 16:0, 16:1, 18:1, and 20:5, strongly dominated (ca. 90%), and the fatty acid profile remained practically unchanged throughout a batch-growth cycle. In nutrient broth, the contribution by “uncommon” fatty acids, mainly i-13:0, 15:0, i-15:0, and 17:1 was generally higher, and increased from 15.4% of total fatty acids in early exponential growth phase to 33.2% in the stationary phase. Reduction of the dilution rate in a chemostat from 0.27 to 0.065 h–1 also led to an almost threefold increase in the proportion of odd-numbered residues at the expense of the even-numbered normal ones. Contrary to this plasticity in the overall fatty acid profile influenced by variations in nutrient composition and availability, the level of eicosapentaenoic acid seemed exclusively dictated by growth temperature. The synthesis of this polyunsaturated fatty acid may be a key regulatory process in maintaining membrane fluidity.

Jens-Petter Jøstensen

Papers

High prevalence of polyunsaturated-fatty-acid producing bacteria in arctic invertebrates

Molecular-phylogenetic, structural and biochemical features of a cold-adapted, marine ichthyosporean near the animal-fungal divergence, described from in vitro cultures

Influence of growth conditions on fatty acid composition of a polyunsaturated-fatty-acid-producing Vibrio species