Hyaluronic acid is a glycosaminoglycan biopolymer widely present throughout connective and epithelial tissue, and has been of great interest for medical and cosmetic applications. In the microbial production of hyaluronic acid, it has not been established to utilize galactose enabling to be converted to UDP-glucuronic acid, which is a precursor for hyaluronic acid biosynthesis. In this study, we engineered Escherichia coli to produce hyaluronic acid from glucose and galactose. The galactose-utilizing Leloir pathway was activated by knocking out the galR and galS genes encoding the transcriptional repressors. Also, the hasA gene from Streptococcus zooepidemicus was introduced for the expression of hyaluronic acid synthase. The consumption rates of glucose and galactose were modulated by knockout of the pfkA and zwf genes, which encode 6-phosphofructokinase I and glucose-6-phosphate dehydrogenase, respectively. Furthermore, the precursor biosynthesis pathway for hyaluronic acid production was manipulated by separately overexpressing the gene clusters galU-ugd and glmS-glmM-glmU, which enable the production of UDP-glucuronic acid and UDP-N-acetyl-glucosamine, respectively. Batch culture of the final engineered strain produced 29.98 mg/L of hyaluronic acid from glucose and galactose. As a proof of concept, this study demonstrated the production of hyaluronic acid from glucose and galactose in the engineered E. coli.

Fluorine-containing compounds are widely used because they have properties required in textiles and coatings for electronic, automotive, and outdoor products. However, fluorinated compounds do not easily break down in nature, which has resulted in their accumulation in the environment as well as the human body. Recently, the enzymatic defluorination of fluorine-containing compounds has gained increasing attention. Here, we review the enzymatic defluorination reactions of fluorinated compounds. Furthermore, we review the enzyme engineering strategies for cleaving C-F bonds, which have the highest dissociation energy found in organic compounds.

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Marine biomasses capable of fixing carbon dioxide have attracted attention as an alternative to fossil resources for fuel and chemical production. Although a simple co-fermentation of fermentable sugars, such as glucose and galactose, has been reported from marine biomass, no previous report has discussed the fine-control of the galactose-to-glucose consumption ratio in this context. Here, we sought to finely control the galactose-to-glucose consumption ratio in the co-fermentation of these sugars using engineered Escherichia coli strains. Toward this end, we constructed E. coli strains GR2, GR2P, and GR2PZ by knocking out galRS, galRS-pfkA, and galRS-pfkA-zwf , respectively, in parent strain W3110. We found that strains W3110, GR2, GR2P, and GR2PZ achieved 0.03, 0.09, 0.12, and 0.17 galactose-to-glucose consumption ratio (specific galactose consumption rate per specific glucose consumption rate), respectively, during co-fermentation. The ratio was further extended to 0.67 by integration of a brief process optimization for initial sugar ratio using GR2P strain. The strategy reported in this study will be helpful to expand our knowledge on the galactose utilization under glucose conditions.

Since its invention, polyethylene (PE) has brought many conveniences to human production and life. In recent years, however, environmental pollution and threats to human health caused by insufficient PE recycling have attracted widespread attention. Biodegradation is a potential solution for preventing PE pollution. In this study, Bacillus subtilis and Bacillus licheniformis, which are widespread in the environment, were examined for their PE degradation abilities. Biodegradation of low-density polyethylene (LDPE) was assessed by weight loss, Fourier transform infrared spectroscopy (FTIR), and high performance liquid chromatography (HPLC) analyses. Weight losses of 3.49% and 2.83% were observed for samples exposed to strains B. subtilis ATCC6051 and B. licheniformis ATCC14580 for 30 days. Optical microscopy revealed obvious structural changes, such as cracks, pits, and roughness, on the surfaces of the microorganism-exposed LDPE sheets. Oxidation of the LDPE sheet surfaces was also demonstrated by the FTIR-based observation of carbon-unsaturated, –OH, –NO, –C=C, and –C–O bonds. These results support the notion that B. subtilis ATCC6051 and B. licheniformis ATCC14580 can degrade PE and could potentially be used as PE-biodegrading microorganisms. Further research is needed to examine potential relevant degradation mechanisms, such as those involving key enzymes.