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Green algae belonging to the genus Ulvales are known to produce ulvan which is one of the main polysaccharide components of their cell wall. Ulvan is composed of 3O-sulfate-rhamnose (Rha3S), glucuronic acid (GlcA), iduronic acid (IduA) and xylose (Xyl) distributed in three disaccharide repetition moieties: [→ 4)- β -D-GlcA-(1 → 4)- α -L-Rha3S-(1 →], [→ 4)- α -L-IdoA-(1 → 4)- α -L-Rha3S(1 →] and [→ 4)- β -D-Xyl-(1 → 4)- α -L-Rha3S(1 →]. The ability of bacteria to degrade complex algal polysaccharides such as ulvan is usually encoded in clusters of genes referred to as polysaccharide utilization loci (PUL). Full saccharification of ulvan is expected to require an ulvan lyase, which cleaves the β -(1 → 4)-glycosidic bond between Rha3S and GluA or IduA through a β -elimination mechanism. In addition, enzymes with β -glucuronyl hydrolase, rhamnosidase, xylosidase and sulfatase activity are also expected. Recently, the genomes of several ulvan degrading bacteria were sequenced, which led to the identification of a new family of polysaccharide lyases family 24 (PL24). In this work, we have continued to mine the genomic data of one of the sequenced strains, Alteromonas sp. LOR. Here we report the identification of an ulvan associated PUL residing between open reading frames ( lor_19 – lor_34 ). This PUL contains a TonB dependent receptor, along with an experimentally verified rhamnosidase, a β -glucuronyl hydrolase and predicted sulfatases. Interestingly, we also identified in the PUL a new ulvan lyase (LOR_29) which showed no homology to previously reported ulvan lyases making it a founding member of yet another new family of polysaccharide lyases (PL25). Finally, this enzyme prompted us to mine other genomes where we identified additional potential ulvan PULs harboring this gene in other bacterial species. Taken together our report provides further insight into ulvan degradation mechanisms in bacteria and reveals a new family of polysaccharide lyases.

Bioethanol is one of the most promising transportation fuels with economic, environmental, and energy benefits. However, currently, the production methodologies and purification technologies of the biofuel industry are not economical. This review demonstrates an economically viable, energy efficient, and sustainable alternative to the state-of-the-art process for bioethanol production from biomass. We have developed a solar-thermal-energy-driven simultaneous saccharification and fermentation (SSF) process for single-step conversion of biomass to bioethanol. In the early stages, aqueous solutions of glucose, starch, or cellulose were fed into a specially designed solar reactor containing instant baker's yeast (Saccharomyces cerevisiae) and the necessary enzymes. The yeast (biocatalyst) was not supplemented by any other nutrient, and it was demonstrated that the same yeast and enzymes could be used for at least two months without any decrease in enzymatic activity. After obtaining very high yields (up to 91% of the theoretical yield) and excellent separation of ethanol from the fermentation broth, the methodology was successfully extended to a continuous-flow single-step conversion of marine algae Ulva rigida to bioethanol (84% of the theoretical yield). Harnessing solar thermal energy for driving the SSF reaction as well as the special design of the solar reactor that facilitates in situ separation of ethanol from the fermentation broth by an evaporation–condensation process make the current method industrially appealing and adoptable for large-scale production. This review explores new avenues for a decentralized power supply based on solar thermal energy. The bioethanol produced in this study was demonstrated as a potential fuel for direct ethanol fuel cells with high current and power density values, and 65% thermodynamic efficiency. In addition, the secondary metabolite glycerol was fully reduced to the value-added product 1,3-propanediol by S. cerevisiae, which is the first example of a fungal strain converting glycerol in situ to 1,3-propanediol. In this review, we aim to discuss the current methodologies and recent developments for bioethanol production from biomass and demonstrate the future aspects of bioethanol production in solar reactors, and strategies to improve process yields as well as the prospects of using a solar reactor to produce other valuable chemicals.

The demand for 1,3-propanediol-based polymers is constantly increasing, necessitating an increase in 1,3-propanediol production. While the processes for the chemical and bacterial synthesis of 1,3-propanediol are well-known, we report for the first time the possibility of glycerol conversion to 1,3-propanediol by a fungal strain. The synthesis of 1,3-propanediol by biological means is extremely lucrative, and to the best of our knowledge, this is the first study focusing on the development of an optimized process for the production of the value-added chemical 1,3-propanediol from what can be considered as industrial waste, glycerol, via fermentation using instant baker's yeast (Saccharomyces cerevisiae). Various glycerol fermentation conditions (aerobic, semi-aerobic, and anaerobic) were tested at different reaction temperatures (25, 30, and 37 °C). Under optimal reaction conditions (anaerobic fermentation at 25 °C), 42.3 wt% 1,3-propanediol yield was achieved with 93.6 wt% glycerol conversion.

Ulvan is a complex sulfated polysaccharide biosynthesized by green seaweed and contains predominantly rhamnose, xylose, and uronic acid sugars. Ulvan-degrading enzymes have only recently been identified and added to the CAZy ( www.cazy.org ) database as family PL24, but neither their structure nor catalytic mechanism(s) are yet known. Several homologous, new ulvan lyases, have been discovered in Pseudoalteromonas sp. strain PLSV, Alteromonas LOR, and Nonlabens ulvanivorans, defining a new family PL25, with the lyase encoded by the gene PLSV_3936 being one of them. This enzyme cleaves the glycosidic bond between 3-sulfated rhamnose (R3S) and glucuronic acid (GlcA) or iduronic acid (IdoA) via a β-elimination mechanism. We report the crystal structure of PLSV_3936 and its complex with a tetrasaccharide substrate. PLSV_3936 folds into a seven-bladed β-propeller, with each blade consisting of four antiparallel β-strands. Sequence conservation analysis identified a highly conserved region lining at one end of a deep crevice on the protein surface. The putative active site was identified by mutagenesis and activity measurements. Crystal structure of the enzyme with a bound tetrasaccharide substrate confirmed the identity of base and acid residues and allowed determination of the catalytic mechanism and also the identification of residues neutralizing the uronic acid carboxylic group. The PLSV_3936 structure provides an example of a convergent evolution among polysaccharide lyases toward a common active site architecture embedded in distinct folds.

The main source of calcium carbonate (CaCO₃) in the ocean comes from the shells of calcifying planktonic organisms, but substantial amounts of CaCO₃ are also produced in fish intestines. The precipitation of CaCO₃ assists fish in intestinal water absorption and aids in whole body Ca²⁺ homeostasis. Here we report that the product formed in the intestinal lumen of the gilt-head seabream, Sparus aurata, is an amorphous calcium carbonate (ACC) phase. With FTIR spectroscopy and SEM imaging, our study shows that the fish-derived carbonates from S. aurata are maintained as a stable amorphous phase throughout the intestinal tract. Moreover, intestinal deposits contained up to 54 mol% Mg²⁺, the highest concentration yet reported in biogenic ACC. Mg is most likely responsible for stabilizing this inherently unstable mineral. The fish carbonates also displayed initial rapid dissolution when exposed to seawater, exhibiting a significant increase in carbonate concentration.