Lipoxygenase activity in the oomyceteSaprolegnia is dependent on environmental cues and reproductive competence

Hydroxy fatty acids in the surface Earth system

Lipids are ubiquitous and highly abundant in a wide range of organisms and have been found in various types of environmental media. These molecules play a crucial role as organic tracers by providing a chemical perspective on viewing the material world, as well as offering a wealth of information on metabolic activities. Among the diverse lipid compounds, hydroxy fatty acids (HFAs) with one to multiple hydroxyl groups attached to the carbon chain stand out as important biomarkers for different sources of organic matter. HFAs are widespread in nature and are involved in biotransformation and oxidation processes in living organisms. The unique chemical and physical properties attributed to the hydroxyl group make HFAs ideal biomarkers in biomedicine and environmental toxicology, as well as organic geochemistry. The molecular distribution patterns of HFAs can be unique and diagnostic for a given class of organisms, including animals, plants, and microorganisms. Thus, HFAs can act as a valuable proxy for understanding the ecological relationships between different organisms and their environment. Furthermore, HFAs have numerous industrial applications due to their higher reactivity, viscosity, and solvent miscibility. This review paper integrates the latest research on the sources and chemical analyses of HFAs, as well as their applications in industrial/medicinal production and as biomarkers in environmental studies. This review article also provides insights into the biogeochemical cycles of HFAs in the surface Earth system, highlighting the importance of these compounds in understanding the complex interactions between living organisms and the environment.

Development and reproduction of Saprolegnia species in biofilms

Saprolegnia spp. can cause mortality and economic losses in freshwater fish and eggs. Biofilm formation is generally regarded as a virulence factor, and biofilms can be an important cause of infection recurrence. Evidence of persistent sources of Saprolegnia infections on fish and eggs in fish farms support the assumption that Saprolegnia spp. might be able to form biofilms. In this study, we aimed to test the ability of Saprolegnia to form biofilms where it can survive, reproduce and resist different chemicals used for its control. Naturally formed biofilms were obtained from laboratory aquaria. Saprolegnia growth within these biofilms was demonstrated with light microscopy and confirmed by isolation. Isolates were identified morphologically and molecularly on the basis of ITS-sequences. Two isolates were identified as Saprolegnia parasitica, a species known to be highly pathogenic for fish, while the other belonged to S. australis. Selected Saprolegnia strains obtained from natural biofilms were then used to establish simple methods for in vitro induction of Saprolegnia biofilm. The ability of Saprolegnia isolates to form biofilms with subsequent production of infective motile zoospores within the biofilm was documented by light and confocal laser scanning microscopy. We demonstrate for the first time that isolates of S. parasitica and S. australis can form biofilm communities together with multiple microorganisms, wherein they grow and reproduce. It is therefore likely that natural biofilms constitute incessant Saprolegnia reservoirs in nature and aquaculture.

The biosynthesis of oxylipins of linoleic and arachidonic acids by the sewage fungus Leptomitus lacteus, including the identification of 8R-Hydroxy-9Z,12Z-octadecadienoic acid

When the sewage fungus Leptomitus lacteus was grown in liquid culture aerobically and then transferred to medium containing long-chain fatty acids, it produced a number of oxygenated fatty acids. From linoleic acid (18:2n-6), the major metabolite produced was R-8-hydroxy-9Z,12Z-octadecadienoic acid (8R-HODE), with additional quantities of 8,11-di-HODE, 11,16-di-HODE, and 11,17-di-HODE. Other fatty acid derivatives identified included 7-HODE, 10-HODE, and 13-hydroxy-octadecamonoenoic acid. Arachidonic acid (20:4n-6) was metabolized primarily to 18- and 19-hydroxy-eicosatetraenoic acids (18- and 19-HETE) also as R enantiomers, along with smaller quantities of 17-HETE, 9-HETE, 14,15-dihydroxy-eicosatrienoic acid and 11,12,19-trihydroxy-eicosatrienoic acid. The oxygenated products of long-chain fatty acids, in particular the biosynthesis of 8R-HODE, a compound classified as a precocious sporulation inducer, were similar to those produced by an unrelated fungal species in the Ascomycota, the take-all fungus Gaeumannomyces graminis. As in G. graminis, the biotransformation of linoleate to 8R-HODE was not significantly inhibited by exposure of the organism to CO. This indicated that the enzyme responsible for 8R-HODE biosynthesis in Leptomitus could be similar to that of G. graminis; yet we did not detect 7,8-di-HODE as a product of 18:2n-6 metabolism as in G. graminis. CO did inhibit the biosynthesis of 14,15-di-HETE, 18-HETE, and 19-HETE in L. lacteus, which suggested the involvement of a cytochrome P450-type monooxygenase. The biosynthesis of 8R-HODE from 18:2n-6 was found to occur in certain cell lysates, specifically in low speed (15,000 x g) supernatant, following cell disruption.

Sterol and steryl ester regulation of phospholipase A2 from the mosquito parasite Lagenidium giganteum

Lagenidium giganteum, a facultative parasite of mosquito larvae, cannot synthesize sterols, and requires an exogenous source of these lipids in order to enter its reproductive cycle. This parasite grows vegetatively in the absence of sterols, but requires cholesterol or structurally related compounds to produce motile zoospores, which are the only stage capable of infecting mosquitoes. Sterols structurally related to cholesterol and some steryl esters inhibited the activity of L. giganteum phospholipase A2 (PLA2), an enzyme that hydrolyzes fatty acids from the sn-2 position of glycerophospholipids. Sterols that induce reproduction inhibited L. giganteum PLA2 activity, while sterols and steroids that do not support sporulation had minimal effect. Most steryl esters had no effect on enzyme activity, but cholesteryl arachidonate (CA) was a potent inhibitor of parasite PLA2. Not all enzymes partly purified using a DEAE-Sephacel column were affected by these lipids, demonstrating selective inhibition of specific enzymes. Potency was enhanced by up to several orders of magnitude if epoxy fatty acids were esterified to the cholesterol nucleus. The steryl ester pool was dynamic during morphogenesis, and the fatty acid composition of the steryl esters did not mimic total cell or membrane (glycerophospholipid) fatty acid composition as L. giganteum proceeded through its growth cycle. Synthesis of CA and monoepoxy CA by the parasite was confirmed using electrospray mass spectrometry and collision-induced dissociation. Steryl derivatives selectively inhibited PLA2 enzymes from bovine pancreas, snake venom, and human cytoplasmic 85-kDa PLA2.

The distribution and taxonomic value of fatty acids and eicosanoids in the Lipomycetaceae and Dipodascaceae

Using radioimmunoassay, blood platelet aggregation studies and GC-MS the existence of prostaglandins in the endomycetalean yeast Dipodascopsis uninucleata was confirmed by our group. These findings triggered the search for similar eicosanoids in the rest of the Endomycetales. We commenced by scanning for the easily detectable precursors of eicosanoids, linoleic- and linolenic acid. We selected two families (i.e. Lipomycetaceae and Dipodascaceae), both producing these precursors, for further investigation. Representative strains of the two families were tested for their ability to grow in the presence of 1 mM aspirin, a specific inhibitor of prostaglandin biosynthesis. In contrast to the lipomycetaceous species the dipodascaceous species were insensitive to this drug. These results were verified when representative strains of both families were investigated for their ability to produce eicosanoids from externally fed radio-labeled arachidonic acid along an aspirin sensitive pathway. Thin layer chromatography of culture extracts, followed by autoradiography, showed that while none of the Dipodascaceae produced aspirin sensitive arachidonic acid metabolites, the members of the Lipomycetaceae tested positive for these metabolites. These findings supported the separation of the lipomycetaceous yeast Dipodascopsis from the Dipodascaceae. The findings also correlate with the delimitation of these yeasts in two families (i.e. Dipodascaceae and Lipomycetaceae). Further investigation indicated that prostaglandin production by the genus Dipodascopsis is mainly associated with ascosporogenesis. Thin layer chromatography of cell extracts from Dipodascopsis tóthii, followed by scintillation counting, indicated the presence of PGF2 alpha and PGE2 during ascosporogenesis.