Research progress in synthesis of astaxanthin by microbial fermentation
Astaxanthin is a value-added terpene with strong antioxidant activity as well as other physiological functions,such as anti-cancer,enhancing immunity,eye protection,and cardio-cerebrovascular protection.Natural astaxanthin mainly comes from algae and aquatic crustaceans such as lobster shell.Astaxanthin presents with stereoisomerism and geometric isomerism,which have different biological activities and applications.Currently,astaxanthin in the market is obtained primarily through natural extraction from Haematococcus pluvialis or Xanthophyllomyces dendrorhous and chemical synthesis as well.While H.pluvialis has a long growth cycle and high light demand,leading to low biomass productivity and extraction rate for high production cost of astaxanthin,X.dendrorhous has a low astaxanthin yield and is easy to degenerate,making them challenging for the large-scale commercial production.The chemical synthesis of astaxanthin involves multiple reactions with complicated processes,producing mixed isomers and various byproducts,which consequently compromises its antioxidant capacity.Moreover,the assimilation and utilization of chemically synthesized astaxanthin in vivo is poor compared to its natural product,making it not suitable for being used by human being.With the continuous development of synthetic biology,microbial fermentation has been developed as an effective way for the commercial production of astaxanthin to better meet consumer demand.At present,astaxanthin-producing microorganisms include bacteria,fungi,and algae.This review introduces astaxanthin's structure,properties,production methods,and processes for its extraction and purification,with an emphasis on natural and engineered biosynthetic pathways.The latest progress in the production of astaxanthin by different microorganisms such as H.pluvialis,Yarrowia lipolytica and Escherichia coli is summarized,along with strategies for increasing astaxanthin production through genetic engineering and fermentation process optimization.Future metabolic engineering strategies are proposed,such as over-expression of astaxanthin synthesis genes,promoters with higher substitution intensity,subcellular localization,metabolic pathway optimization,etc,to increase astaxanthin yield for wide usage in food,medical,cosmetic and feed industries.
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