Efficient conversion of mannitol derived from brown seaweed to fructose for fermentation with a thraustochytrid

Systematic review on marine carbon source-mannitol: Applications in synthetic biology

Mannitol, one of the most widespread sugar alcohols, has been integral to daily human life for two centuries. Global population growth and competition for freshwater, food, and land have prompted a shift in the fermentation industry from terrestrial to marine raw materials. Mannitol is a readily available carbohydrate in brown seaweed from the ocean and possess a higher reducing power than glucose, making it a promising substrate for biological manufacturing. This has spurred numerous explorations into converting mannitol into high-value chemicals. Researchers have engineered microorganisms to utilize mannitol in various synthetic biological applications, including: (1) employing mannitol as an inducer to control the activation and deactivation of genetic circuits; (2) using mannitol as a carbon source for synthesizing high-value chemicals through biomanufacturing. This review summarizes the latest advances in the application of mannitol in synthetic biology. AIM OF REVIEW: The aim is to present a thorough and in-depth knowledge of mannitol, a marine carbon source, and then use this carbon source in synthetic biology to improve the competitiveness of biosynthetic processes. We outlined the methods and difficulties of utilizing mannitol in synthetic biology with a variety of microbes serving as hosts. Furthermore, future research directions that could alleviate the carbon catabolite repression (CCR) relationship between glucose and mannitol are also covered. EXPECTED CONTRIBUTIONS OF REVIEW: Provide an overview of the current state, drawbacks, and directions for future study on mannitol as a carbon source or genetic circuit inducer in synthetic biology.

Proximate analysis and fatty acid, mineral and soluble carbohydrate profiles of some brown macroalgae collected from Türkiye coasts

In this study, the fatty acid, carbohydrate, and mineral profiles and proximate composition of Halopteris scoparia, Padina pavonica, Zanardinia typus, Cladostephus spongiosum, Sargassum vulgare, and Sargassum acinarium brown macroalgae collected from Türkiye seas were determined. According to the results, the ash and total carbohydrate contents of all macroalgae ranged from 20.79 to 53.49% in dry weight (dw) and from 15.32 to 55.13% dw, respectively. Their protein, lipid and crude fiber contents changed between 4.22 and 9.89% dw, 0.25 and 0.90% dw, and 12.28 and 16.01% dw, respectively. Palmitic acid (29.36-48.55% dw) and oleic acid (8.92-20.92% dw) were at the highest levels in all brown macroalgae. In addition, they included prominent levels of saturated fatty acids (51.87-69.56% dw of total fatty acid content). Magnesium (6.97-18.78 mg/kg dw), potassium (1.34-3.78 mg/kg dw), iron (1.27-8.24 mg/kg dw), and manganese (63.10-252.23 μg/kg dw) were found to be the major minerals. The main soluble carbohydrates of macroalgae were found to be mannitol (1149.99-8676.31 mg/kg dw), glucose (368.78-1305.59 mg/kg dw), myo-inositol (225.96-956.78 mg/kg dw), fructose (137.05-689.21 mg/kg dw), and sucrose (189.55-328.06 mg/kg dw). This study revealed that brown macroalgae are particularly rich in potassium, magnesium, iron, manganese, and zinc and they may have potential for use in the food industry.

Substrate degradation pathways, conserved functions and community composition of the hindgut microbiota in the herbivorous marine fish Kyphosus sydneyanus

Symbiotic gut microbiota in the herbivorous marine fish Kyphosus sydneyanus play an important role in digestion by converting refractory algal carbohydrate into short-chain fatty acids. Here we characterised community composition using both 16S rRNA gene amplicon sequencing and shotgun-metagenome sequencing. Sequencing was carried out on lumen and mucosa samples (radial sections) from three axial sections taken from the hindgut of wild-caught fish. Both lumen and mucosa communities displayed distinct distributions along the hindgut, likely an effect of the differing selection pressures within these hindgut locations, as well as considerable variation among individual fish. In contrast, metagenomic sequences displayed a high level of functional similarity between individual fish and gut sections in the relative abundance of genes (based on sequencing depth) that encoded enzymes involved in algal-derived substrate degradation. These results suggest that the host gut environment selects for functional capacity in symbionts rather than taxonomic identity. Functional annotation of the enzymes encoded by the gut microbiota was carried out to infer the metabolic pathways used by the gut microbiota for the degradation of important dietary substrates: mannitol, alginate, laminarin, fucoidan and galactan (e.g. agar and carrageenan). This work provides the first evidence of the genomic potential of K. sydneyanus hindgut microbiota to convert highly refractory algal carbohydrates into metabolically useful short-chain fatty acids.

Unexpectedly high thermostability of an NADP-dependent malic enzyme from a psychrophilic bacterium, Shewanella livingstonensis Ac10

Psychrophilic enzymes are generally active at low temperatures, and their functions have attracted much interest in food processing, biochemical research, and chemical industry. However, their activities are usually lost above their growth temperature because of their flexible and unstable structure. Here, we unexpectedly found that a homodimeric NADP-dependent malic enzyme from a psychrophilic bacterium, Shewanella livingstonensis Ac10 (SL-ME) showed sufficient activity with 60°C treatment, similar to its counterpart from mesophilic Escherichia coli (MaeB). Consistently, SL-ME and MaeB irreversibly denatured at 71.9°C and 64.5°C, respectively. Therefore, SL-ME shows robust catalytic activity, which appears to be advantageous for its application in the bioconversion of NADP to NADPH, an essential ingredient for membrane phospholipid synthesis.

Psychrophile-based simple biocatalysts for effective coproduction of 3-hydroxypropionic acid and 1,3-propanediol

3-Hydroxypropionic acid (3-HP) and 1,3-propanediol (1,3-PDO) have tremendous potential markets in many industries. This study evaluated the simultaneous biosynthesis of the 2 compounds using the new psychrophile-based simple biocatalyst (PSCat) reaction system. The PSCat method is based on the expression of glycerol dehydratase, 1,3-propanediol dehydrogenase, and aldehyde dehydrogenase from Klebsiella pneumoniae in Shewanella livingstonensis Ac10 and Shewanella frigidimarina DSM 12253, individually. Heat treatment at 45 °C for 15 min deactivated the intracellular metabolic flux, and the production process was started after adding substrate, cofactor, and coenzyme. In the solo production process after 1 h, the maximum production of 3-HP was 62.0 m m. For 1,3-PDO, the maximum production was 25.0 m m. In the simultaneous production process, productivity was boosted, and the production of 3-HP and 1,3-PDO increased by 13.5 and 4.9 m m, respectively. Hence, the feasibility of the individual production and the simultaneous biosynthesis system were verified in the new PSCat approach.

Two-level factorial analysis of the effect of fructose on DHA biosynthetic capacity of Aurantiochytrium sp. SW1

Thraustochytrids are getting increasingly popular due to their high potential role as alternative producers of the high-valued ω-3 polyunsaturated fatty acids (PUFA), docosahexaenoic acid (DHA). While most thraustochytrids prefer glucose as the major carbon source, few strains have been reported to prefer fructose. One such strain is Aurantiochytrium sp. SW1. In this study, the effect of fructose on DHA accumulation by SW1 was investigated using a two-level full factorial design. Besides, biomass, lipid and DHA accumulation profiles of SW1 cultivated in fructose and glucose media were compared. Results revealed that fructose has a very significant positive effect on the volumetric DHA content. Meanwhile, its involvement in affecting DHA biosynthetic capacity, though significant, is not very profound. It was also found that when cultivated in fructose medium, SW1 had a less steep log phase compared to that of glucose medium. However, after 48h of cultivation, biomass and lipid accumulation in fructose medium outweighed the other. Volumetric DHA content in fructose medium at 96h was 11% higher than that of glucose medium. Overall, fructose was found to be a more suitable substrate for biomass, lipid and DHA accumulation in SW1 compared to the conventional source, glucose.

Improvement of fatty acid productivity of thraustochytrid, Aurantiochytrium sp. by genome editing

Thraustochytrid strains belonging to the genus Aurantiochytrium accumulate significant amounts of lipids including polyunsaturated fatty acids and carotenoids and, therefore, are expected to be used for industrial production of various valuable materials. Although various efforts such as chemical mutagenesis and homologous gene recombination have been made to improve lipid productivity of Aurantiochytrium species, low specificity and efficiency in the conventional methods hinder the research progress. Here, we attempted to apply a genome editing technology, the CRISPR-Cas9 system as an alternative molecular breeding technique for Aurantiochytrium species to accelerate the metabolic engineering. The efficiency of specific gene knock-in by the homologous recombination increased more than 10-folds by combining the CRISPR-Cas9 system. As a result of disrupting the genes associated with β-oxidation of fatty acids by the improved method, the genome edited strains with higher fatty acid productivity were isolated, demonstrating for the first time that the CRISPR-Cas9 system was effective for molecular breeding of the strains in the genus Aurantiochytrium to improve lipid productivity.

Seaweed Bioethanol Production: A Process Selection Review on Hydrolysis and Fermentation

The rapid depletion and environmental concerns associated with the use of fossil fuels has led to extensive development of biofuels such as bioethanol from seaweeds. The long-term prospect of seaweed bioethanol production however, depends on the selection of processes in the hydrolysis and fermentation stages due to their limiting effect on ethanol yield. This review explored the factors influencing the hydrolysis and fermentation stages of seaweed bioethanol production with emphasis on process efficiency and sustainable application. Seaweed carbohydrate contents which are most critical for ethanol production substrate selection were 52 ± 6%, 55 ± 12% and 57 ± 13% for green, brown and red seaweeds, respectively. Inhibitor formation and polysaccharide selectivity were found to be the major bottlenecks influencing the efficiency of dilute acid and enzymatic hydrolysis, respectively. Current enzyme preparations used, were developed for starch-based and lignocellulosic biomass but not seaweeds, which differs in polysaccharide composition and structure. Also, the identification of fermenting organisms capable of converting the heterogeneous monomeric sugars in seaweeds is the major factor limiting ethanol yield during the fermentation stage and not the SHF or SSF pathway selection. This has resulted in variations in bioethanol yields, ranging from 0.04 g/g DM to 0.43 g/g DM.