Fucoxanthin from marine microalgae: A promising bioactive compound for industrial production and food application.

Fucoxanthin attracts increasing attentions due to its potential health benefits, which has been exploited in several food commodities. However, fucoxanthin available for industrial application is mainly derived from macroalgae, and is not yet sufficiently cost-effective compared with microalgae. This review focuses on the strategies to improve fucoxanthin productivity and approaches to reduce downstream costs in microalgal production. Here we comprehensively and critically discuss ways and methods to increase the cell growth rate and fucoxanthin content of marine microalgae, including strain screening, condition optimization, design of culture mode, metabolic and genetic engineering, and scale-up production of fucoxanthin. The approaches in downstream processes provide promising alternatives for fucoxanthin production from marine microalgae. Besides, this review summarizes fucoxanthin improvements in solubility and bioavailability by delivery system of emulsion, nanoparticle, and hydrogel, and discusses fucoxanthin metabolism with gut microbes. Fucoxanthin production from marine microalgae possesses numerous advantages in environmental sustainability and final profits to meet incremental global market demands of fucoxanthin. Strategies of adaptive evolution, multi-stage cultivation, and bioreactor improvements have tremendous potentials to improve economic viability of the production. Moreover, fucoxanthin is promising as the microbiota-targeted ingredient, and nanoparticles can protect fucoxanthin from external environmental factors for improving the solubility and bioavailability.

Regulation of Virulence Factors Expression During the Intestinal Colonization of Vibrio parahaemolyticus.

Colonization and adhesion are the key steps for Vibrio parahaemolyticus to infect human body and cause seafood poisoning. However, at present, there is a lack of systematic review on the regulation of virulence factors expression during the intestinal colonization of V. parahaemolyticus. This review aims to describe the virulence factors associated with the colonization and adhesion of V. parahaemolyticus (multivalent adhesion molecule 7, enolase secretion, use of flagella, biofilm formation, and the action of secretion systems) and focuses on the aspects that affect these processes in V. parahaemolyticus, including secretion systems, quorum sensing (QS), and the human gastrointestinal tract. V. parahaemolyticus regulates the expression of virulence factors by forming a virulence regulation network through QS and the core regulator, ToxR, which contributes to the early colonization of the pathogen. In the virulence regulation network, the secretion systems, type III and type VI secretion systems, help V. parahaemolyticus adhere to the distal end of the small intestine by secreting effectors that induce the lysis of epithelial cells and change the shape of the intestinal lining, which provides nutrients and a suitable environment for its growth. This review summarizes the research progress in recent years on the virulence factors associated with the colonization and adhesion of V. parahaemolyticus, which provides valuable information for the safety control of marine food.

Improvement of the Catalytic Ability of a Thermostable and Acidophilic ß-Mannanase Using a Consensus Sequence Design Strategy.

In order to improve the catalytic efficiency of a thermostable and acidophilic ß-mannanase (ManAK; derived from marine Aspergillus kawachii IFO 4308), three mutants were designed by amino acid sequence consensus analysis with a second ß-mannanase (ManCbs), which also belongs to the glycoside hydrolase family 5 (GH5) and has excellent catalytic efficiency. Three mutants were constructed and their biochemical characteristics were measured after heterologous expression in Pichia pastoris. The results revealed that the kcat/Km values of the three recombinant mannanases ManAKC292V, ManAKL293V, and ManAKL294H were enhanced by 303.0, 280.4, and 210.1%, respectively. Furthermore, ManAKL293V showed greater thermostability than ManAK, retaining 36.5% of the initial enzyme activity after incubation at 80°C for 5min. This study therefore provides a rational design strategy based on consensus sequence analysis to develop industrially valuable ß-mannanase for future applications in marine aquafeed.

Enzymatic Preparation of Low-Molecular-Weight Laminaria japonica Polysaccharides and Evaluation of Its Effect on Modulating Intestinal Microbiota in High-Fat-Diet-Fed Mice.

Recent studies have shown that seaweed polysaccharides can ameliorate high-fat-diet (HFD)-induced metabolic syndromes associated with the regulatory function of gut microbiota. However, kelp, a natural source of seaweed polysaccharides, is highly viscous, making it difficult to prepare dietary fiber by simple degradation. Therefore, we developed a novel method of preparing low-molecular-weight polysaccharides from Laminaria japonica by combining high-pressure pretreatment and composite enzymatic degradation and evaluated the obesity prevention activity of these polysaccharides. Seaweed L. japonica polysaccharides (SJP) were rapidly utilized by the human fecal microbiota in vitro, resulting in the generation of short-chain fatty acids (SCFAs), specifically acetate and propionate. The in vivo effects of SJP on the intestinal microbiota were also investigated using HFD-fed C57BL/6J mice. SJP reduced weight gain and fat deposition in HFD-fed mice and increased the concentration of total SCFAs, including acetate, propionate, and butyrate in the feces. SJP ameliorated HFD-induced gut microbiota dysbiosis, resulting in increased abundance of Faecalibaculum, Romboutsia, and Clostridium sensu stricto 1 and decreased abundance of Blautia and Lactobacillus. Further, SJP enhanced the abundance of Akkermansia muciniphila in mice provided with HFD and normal chow. Single-strain culture experiments also revealed that SJP promoted the growth of A. muciniphila. This study highlights the potential use of SJP, prepared using composite enzymatic degradation (cellulase and recombinant alginate lyase), in preventing obesity and restoring intestinal homeostasis in obese individuals.