Hyaluronic acid (HA) is a natural and linear polymer composed of repeating disaccharide units of β-1, 3-N-acetyl glucosamine and β-1, 4-glucuronic acid with a molecular weight up to 6 million Daltons. With excellent viscoelasticity, high moisture retention capacity, and high biocompatibility, HA finds a wide-range of applications in medicine, cosmetics, and nutraceuticals.Traditionally HA was extracted from rooster combs, and now it is mainly produced via streptococcal fermentation. Recently the production of HA via recombinant systems has received increasing interest due to the avoidance of potential toxins. This work summarizes the research history and current commercial market of HA, and then deeply analyzes the current state of microbial production of HA byStreptococcus zooepidemicusand recombinant systems, and finally discusses the challenges facing microbial HA production and proposes several research outlines to meet the challenges.

Chondroitin sulfate (CS) is widely applied in the medical, clinical, and nutraceutical fields. However, all commercialized CS is extracted from animal tissues, which is associated with many problems, such as heavy reliance on antibiotics, animal excrement waste and long breeding time. Here, we developed a promising new green route for the de novo biosynthesis of non-animal CS from methanol, a one-carbon compound, using the engineered Pichia pastoris cell factory. Firstly, three exogenous genes, namely kfoC and kfoA from Escherichia coli K4 and tuaD from Bacillus subtilis, were introduced into P. pastoris to construct the chondroitin synthesis pathway, which yielded 5.5 mg L⁻¹ chondroitin. After optimizing the expression of committed enzymes by codon optimization, the production of chondroitin improved by approximately 35-fold to 189.8 mg L⁻¹. Thereafter, 6 kinds of Kozak sequences and 10 different endogenous promoters were compared and applied to achieve the expression of active chondroitin-4-O-sulfotransferase (41.3 U L⁻¹). After integrating the chondroitin biosynthesis and sulfonation modules, the engineered strain, Pp006, successfully produced 182.0 mg L⁻¹ CSA [GlcA-GalNAc (4S)] with a sulfation degree of 1.1%. We further improved the sulfation degree to 2.8% by strengthening the 3′-phosphoadenosine-5′-phosphosulfate (PAPS) supply with the overexpression of adenosine-5′-triphosphate sulfurylase and adenosine 5′-phosphosulfate kinase. In the fed-batch cultivation, the final titer of CSA reached 2.1 g L⁻¹ and the sulfation degree increased to 4.0%. Moreover, the results suggest that the P. pastoris cell factory could be used as a green route to produce other sulfated glycosaminoglycans.