Effects of Growth Medium Variation on the Nutri-Functional Properties of Microalgae Used for the Enrichment of Ricotta.

Research background: Microalgae represent an emergent sustainable source of bioactive compounds such as antioxidants, vitamins, minerals and polyunsaturated fatty acids that can ameliorate the nutritional characteristics of foods. The biochemical composition of microalgae could be modulated by varying the culture conditions to enhance the accumulation of biomolecules of interest. The aim of this work is to optimise the nutri-functional properties of two microalgae that can be used in food production. Experimental approach: Nannochloropsis gaditana L2 and Chlorella sp. SM1 were screened for growth, biochemical composition and radical scavenging activity employing four different growth media (algal, BG-11, f/2 and Conway) with different nutrient composition. The feasibility of using Chlorella sp. SM1 cultivated in BG-11 medium, in an under-investigated Mediterranean dairy product ricotta cheese and its effect on the sensory attributes was investigated. Additionally, Arthrospira platensis was used as reference in sensory analysis. Results and conclusions: Nitrate- and phosphate-rich media (BG-11 and algal) enhanced the biomass productivity. However, the highest lipid production (23.10 and 11.86 mg/(L·day) by strains SM1 and L2 respectively) and carbohydrate content (34.79 and 44.84% by SM1 and L2 respectively) were obtained with the nitrate-deficient f/2 medium. Regardless of the used medium, the lipid profile of Chlorella sp. SM1 and N. gaditana L2 remained adequate for different applications with >50% C16-18 as the main fatty acids. Significant increase in oleic acid (C18:1) content was recorded in response to nitrogen deficiency, being the highest in SM1 in f/2 medium (34%). Nitrogen deficiency was also found to enhance phenolic compound (expressed as gallic acid equivalents, 48.8 and 35.1 mg/g in SM1 and L2 respectively) and carotenoid contents (2.2 and 2.0 mg/g in SM1 and L2 respectively). Due to its interesting antioxidant potential, Chlorella sp. SM1 was used at different mass fractions (0.2, 1 and 1.5%) to enrich the ricotta cheese. The sample with 0.2% Chlorella sp. SM1 was found to give the most appreciated product. Novelty and scientific contribution: This study presents the production of an innovative ricotta cheese using Chlorella sp. as a functional ingredient, without altering the manufacturing procedure, while maintaining acceptable sensorial characteristics. The biochemical composition of the used strains varied depending on the culture medium composition, which enabled the accumulation of phytonutrients of interest.

Anaerobic oxidation of long-chain n-alkanes by the hyperthermophilic sulfate-reducing archaeon, Archaeoglobus fulgidus.

The thermophilic sulfate-reducing archaeon Archaeoglobus fulgidus strain VC-16 (DSM 4304), which is known to oxidize fatty acids and n-alkenes, was shown to oxidize saturated hydrocarbons (n-alkanes in the range C10-C21) with thiosulfate or sulfate as a terminal electron acceptor. The amount of n-hexadecane degradation observed was in stoichiometric agreement with the theoretically expected amount of thiosulfate reduction. One of the pathways used by anaerobic microorganisms to activate alkanes is addition to fumarate that involves alkylsuccinate synthase as a key enzyme. A search for genes encoding homologous enzymes in A. fulgidus identified the pflD gene (locus-tag AF1449) that was previously annotated as a pyruvate formate lyase. A phylogenetic analysis revealed that this gene is of bacterial origin and was likely acquired by A. fulgidus from a bacterial donor through a horizontal gene transfer. Based on three-dimensional modeling of the corresponding protein and molecular dynamic simulations, we hypothesize an alkylsuccinate synthase activity for this gene product. The pflD gene expression was upregulated during the growth of A. fulgidus on an n-alkane (C16) compared with growth on a fatty acid. Our results suggest that anaerobic alkane degradation in A. fulgidus may involve the gene pflD in alkane activation through addition to fumarate. These findings highlight the possible importance of hydrocarbon oxidation at high temperatures by A. fulgidus in hydrothermal vents and the deep biosphere.

Characterization of Microaerobacter geothermalis gen. nov., sp. nov., a novel microaerophilic, nitrate- and nitrite-reducing thermophilic bacterium isolated from a terrestrial hot spring in Tunisia.

A novel thermophilic anaerobic and microaerophilic bacterium (optimal growth in the presence of 5-10% O(2)), strain Nad S1(T) was isolated from the terrestrial hot spring of Hammam Sidi Jdidi, Nabeul, Tunisia. Cells were motile rods having a Gram-positive cell wall structure. Strain Nad S1(T) grew optimally at 55 degrees C (range 37-70 degrees C). Optimum pH for growth was 6.5-7.0. It was halotolerant growing with NaCl up to 7% (optimum concentration 1.5-3.0%). It grew chemoorganotrophically on various carbohydrates, organic-acids and amino-acids as energy sources, or chemolithotrophically on H(2) using nitrate, as terminal electron acceptor. Beside oxygen (under microaerobic conditions) and nitrate, nitrite was also used. Nitrate was completely reduced to N(2). No fermentation occurred. The genomic DNA G + C content was 41.8 mol%. Based on 16S rRNA gene sequence analysis, strain Nad S1(T) belongs to the Bacillaceae family within the class 'Bacilli'. Because of its phylogenetic and phenotypic characteristics, we propose this isolate to be assigned as a novel genus and a novel species within the domain Bacteria, Microaerobacter geothermalis gen. nov., sp. nov. The type strain is Nad S1(T) (=DSM 22679(T) =JCM 16213(T)).

Anaerobic oxidation of fatty acids and alkenes by the hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus.

Archaeoglobus fulgidus oxidizes fatty acids (C(4) to C(18)) and n-alk-1-enes (C(12:1) to C(21:1)) in the presence of thiosulfate as a terminal electron acceptor. End products of metabolism were CO(2) and sulfide. Growth on perdeuterated hexadecene yielded C(15)- to C(17)-labeled fatty acids as metabolites, thus confirming the ability of A. fulgidus to oxidize alkyl chains.