Production of arachidonic and eicosapentaenoic acids by the marine oomycete Halophytophthora

Unravelling the Lipids Content and the Fatty Acid Profiles of Eight Recently Described Halophytophthora Species and H. avicennae from the South Coast of Portugal

In this study, mycelia of eight recently described species of Halophytophthora and H. avicennae collected in Southern Portugal were analysed for lipids and fatty acids (FA) content to evaluate their possible use as alternative sources of FAs and understand how each species FAs profile relates to their phylogenetic position. All species had a low lipid percentage (0.06% in H. avicennae to 0.28% in H. frigida). Subclade 6b species contained more lipids. All species produced monounsaturated (MUFA), polyunsaturated (PUFA) and saturated (SFA) FAs, the latter being most abundant in all species. H. avicennae had the highest FA variety and was the only producer of γ-linolenic acid, while H. brevisporangia produced the lowest number of FAs. The best producer of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) was H. thermoambigua with 3.89% and 9.09% of total FAs, respectively. In all species, palmitic acid (SFA) was most abundant and among the MUFAs produced oleic acid had the highest relative percentage. Principal component analysis (PCA) showed partial segregation of species by phylogenetic clade and subclade based on their FA profile. H. avicennae (Clade 4) differed from all other Clade 6 species due to the production of γ-linolenic and lauric acids. Our results disclosed interesting FA profiles in the tested species, adequate for energy (biodiesel), pharmaceutical and food industries (bioactive FAs). Despite the low amounts of lipids produced, this can be boosted by manipulating culture growth conditions. The observed interspecific variations in FA production provide preliminary insights into an evolutionary background of its production.

Speaking the language of lipids: the cross-talk between plants and pathogens in defence and disease

Lipids and fatty acids play crucial roles in plant immunity, which have been highlighted over the past few decades. An increasing number of studies have shown that these molecules are pivotal in the interactions between plants and their diverse pathogens. The roles played by plant lipids fit in a wide spectrum ranging from the first physical barrier encountered by the pathogens, the cuticle, to the signalling pathways that trigger different immune responses and expression of defence-related genes, mediated by several lipid molecules. Moreover, lipids have been arising as candidate biomarkers of resistance or susceptibility to different pathogens. Studies on the apoplast and extracellular vesicles have been highlighting the possible role of lipids in the intercellular communication and the establishment of systemic acquired resistance during plant-pathogen interactions. From the pathogen perspective, lipid metabolism and specific lipid molecules play pivotal roles in the pathogen's life cycle completion, being crucial during recognition by the plant and evasion from the host immune system, therefore potentiating infection. Studies conducted in the last years have contributed to a better understanding of the language of lipids during the cross-talk between plants and pathogens. However, it is essential to continue exploring the knowledge brought up to light by transcriptomics and proteomics studies towards the elucidation of lipid signalling processes during defence and disease. In this review, we present an updated overview on lipids associated to plant-pathogen interactions, exploiting their roles from the two sides of this battle.

Salinity, pH and temperature growth ranges of Halophytophthora isolates suggest their physiological adaptations to mangrove environments

Species of Halophytophthora are early colonisers of fallen mangrove leaves in the tropics but recently found commonly in temperate areas. In mangrove habitats, temperature and salinity change rapidly daily (high/low tide) and seasonally (summer/winter, rainy/dry seasons). Mangrove organisms have to develop adaptive strategies to thrive in such a physiologically challenging environment. In this study, growth of three isolates of Halophytophthora avicenniae and two isolates of H. batemanensis was tested under combined effects of 3 temperatures (15°C, 25°C, 37°C), 3 pHs (6, 7, 8) and 4 salinities (4 ‰, 8 ‰, 16 ‰, 32 ‰). No/little growth was observed at 37°C and growth saturation occurred earlier at 25°C than at 15°C. The log phase of growth was steeper at pH 6 than pH 7 and 8. Temperature and pH were found to exert a greater effect on growth than salinity. Generally, a reduction of growth rate was observed at pH 8 and 15°C. Increase in salinity caused a slight decrease in growth, most noticeable at 32 ‰. The wide growth ranges of temperature, salinity and pH of Halophytophthora isolates suggest that they are well adapted to the physical and chemical conditions of mangrove habitats.

Marine Oomycetes (Halophytophthora and Salispina): A Potential Source of Fatty Acids with Cytotoxic Activity Against Breast Adenocarcinoma Cells (MCF7)

Marine oomycetes are ubiquitous, fungus-like eukaryotes known to produce fatty acids with potential anticancer activity. The long chain omega-3 and omega-6 fatty acids are currently popular and considered as safe when used as nutraceuticals in cancer treatment. In this study, crude fatty acids from three marine oomycetes, Halophytophthora spp. (T12GP1 and T12YBP2) and Salispina hoi (USTCMS 1611), were explored for their cytotoxic and apoptotic potentials against human breast adenocarcinoma cells (MCF7) and normal human dermal fibroblasts (HDFn). Extracts from mycelia mats consisted of diverse saturated, monounsaturated, and polyunsaturated fatty acids such as linoleic, α-linolenic, γ-linolenic, eicosatrienoic and eicosapentaenoic acids. The crude fatty acids from all three oomycetes in in vitro assays for cytotoxicity showed no toxicity (30% toxicity values) on HDFn cells. On MCF7 cells, however, IC₅₀ values of 23.44, 15.63, and 26.15 µg/mL were obtained with extracts from Halophytophthora T12GP1 and T12YBP2 and S. hoi, respectively. Treated MCF7 cells exhibited deformed cell membrane in MTT assay and also aggregation of DNA and disruption of nuclear membrane aggregation in nuclear staining; further, green signals indicative of apoptosis was recorded in caspase 3/7 assay.

Growth and fatty acid profiles of Halophytophthora vesicula and Salispina spinosa from Philippine mangrove leaves

Studies on marine-sourced fatty acids have gathered significant interest recently as an important component of aquaculture feeds and of biofuel production. Of the organisms capable of producing fatty acids, marine oomycetes are promising model organisms. One group of marine oomycetes are the Halophytophthora spp. which is known to have an important role in leaf decomposition, thereby changing the plant debris into exudates which are usable to consumers in the mangrove ecosystems. This study reports the three mangrove oomycetes isolated from Philippine mangrove forests, identified herein as Halophytophthora vesicula AK1YB2 (Aklan), H. vesicula PQ1YB3 (Quezon) and Salispina spinosa ST1YB3 (Davao del Norte). These isolates were subjected to growth analyses using varying incubation parameters (salinity level and pH), and for fatty acid production. Results revealed the presence of different fatty acids such as Arachidonic acid, Linoleic acid and Vaccenic acid when grown on V8S and PYGS media. This study is the first observation of fatty acids from S. spinosa and H. vesicula from the Philippines. SIGNIFICANCE AND IMPACT OF THE STUDY: Tropical Philippines straddling west of the Pacific Ocean and East of South China Sea is rich in marine and estuarine oomycetes. These micro-organisms, hitherto poorly known and unstudied in the country, play an important role in the nutritive cycle of the mangrove ecosystem. Due to the increasing demand for an alternative source of fatty acids, species of Oomycetes isolated from select mangrove forests in Luzon, Visayas and Mindanao were analysed for their fatty acid contents. Prospects for industrially-important fatty acids make these Oomycetes all-important to study in applied microbiology in the Philippine setting where these structurally simple micro-organisms abound.

TLC Screening Profile of Secondary Metabolites and Biological Activities of Salisapilia tartarea S1YP1 Isolated from Philippine Mangroves

The Salisapilia species are estuarine oomycetes of the mangrove and saltmarsh ecosystem. To date, reports on the secondary metabolites and biological activities of these microorganisms are wanting. In this study, secondary metabolites in broth ethyl acetate extracts (BEAE) and mycelial ethyl acetate extracts (MEAE) of Salisapilia tartarea S1YP1 isolated from yellow senescent mangrove leaves were screened by Thin Layer Chromatography (TLC). Extracts were assayed for antioxidant, antibacterial, α- glucosidase inhibition, and cytotoxic activity. The TLC detected anthraquinones, anthrones, flavonoids, phenols, and triterpenes in both BEAE and MEAE. Coumarins were detected in BEAE but not in MEAE. Quantifying the total phenolics and total flavonoids content of the extracts in terms of gallic acid and quercetin equivalents, respectively shows that BEAE has higher total phenolic and flavonoid contents than MEAE. BEAE exhibited significant antioxidant activities through measurements of free radical scavenging activity against DPPH, hydroxyl, nitric oxide, and superoxide anion radicals as well as the ability to chelate Fe²⁺ metal ion. BEAE significantly inhibited in a dose-dependent manner α-glucosidase activity and selectively inhibited HepG2 cell proliferation. Antioxidant, α- glucosidase inhibitory, and cytotoxic activities have not been observed for MEAE. Both BEAE and MEAE do not have antibacterial activity.

Identification of Lipid Markers of Plasmopara viticola Infection in Grapevine Using a Non-targeted Metabolomic Approach

The Oomycete Plasmopara viticola is responsible for downy mildew, which is one of the most damaging grapevine diseases. Due to the strictly biotrophic way of life of P. viticola, its metabolome is relatively poorly characterized. In this work, we have used a mass spectrometry-based non-targeted metabolomic approach to identify potential Plasmopara-specific metabolites. This has led to the characterization and structural elucidation of compounds belonging to three families of atypical lipids, which are not detected in healthy grapevine tissues. These lipids include ceramides and derivatives of arachidonic and eicosapentaenoic acid, most of which had not been previously described in Oomycetes. Furthermore, we show that these lipids can be detected in Plasmopara-infected tissues at very early stages of the infection process, long before the appearance the first visible symptoms of the disease. Therefore, the potential use of these specific lipids as markers to monitor the development of P. viticola is discussed.

Integrated omics study of lipid droplets from Plasmodiophora brassicae

Plasmodiophora brassicae causes clubroot disease in cruciferous. In this report, lipid droplets were observed in the resting spores of P. brassicae. 295 lipid droplet-associated proteins were identified and categorized into nine groups. Transcriptome analysis of these proteins during three different zoosporic stages revealed differences in gene expression pattern. GO enrichment analysis revealed that these proteins associated with lipid droplets were mainly linked to biosynthesis and metabolism. GC-MS analysis revealed that lipid droplets contain seven types of free fatty acids: saturated fatty acids C16:0 and C18:0, and unsaturated fatty acids C18:1Δ9, C18:1Δ11, C18:2, C20:4 and C20:5. P. brassicae accumulated a large amount of triacylglycerols (TAGs). We systematically analyzed the putative proteins involved in TAG biosynthesis and its metabolic pathway. KEGG pathway analysis defined 3390 genes, including 167 genes involved in lipid metabolism. Transcriptome analysis revealed that 162 candidate enzymes involved in lipid metabolism were differential expressed. Our omics studies are the first to investigate the lipid droplet organelles in P. brassicae, providing a reference resource to study protist lipid droplets.