Pathway engineering of Bacillus subtilis for microbial production of N-acetylglucosamine

Glucosamine (GlcN) and its acetylated derivative, N-acetylglucosamine (GlcNAc), are widely used in nutraceutical and pharmaceutical industries. Currently, GlcN and GlcNAc are mainly produced by hydrolysis from crab and shrimp shells, which can cause severe environmental pollution and carries the potential risk of allergic reactions. In this study, we attempted to achieve microbial production of GlcNAc by pathway engineering of Bacillus subtilis 168. Specifically, glmS (encoding GlcN-6-phosphate synthase) from B. subtilis 168 and GNA1 (encoding GlcNAc-6-phosphate N-acetyltransferase) from Saccharomyces cerevisiae S288C were firstly co-overexpressed in B. subtilis; the level of GlcNAc reached 240 mg/L in shake flask culture. Next, nagP, encoding the GlcNAc-specific enzyme of phosphotransferase system, was deleted to block the importation of extracellular GlcNAC, thus improving GlcNAc production to 615 mg/L in shake flask culture. Then, nagA (encoding GlcNAc-6-phosphate deacetylase), gamA (encoding GlcN-6-phosphate deaminase), and nagB (encoding GlcN-6-phosphate deaminase) were deleted to block the catabolism of intracellular GlcNAc, thereby further increasing the GlcNAc titer to 1.85 g/L in shake flask culture. Finally, microbial production of GlcNAc by the engineered B. subtilis 168 was conducted in a 3-L fed-batch bioreactor, and the GlcNAc titer reached 5.19 g/L, which was 2.8-fold of that in shake flask culture. This is the first report regarding the pathway engineering of B. subtilis for microbial production of GlcNAc, and provides a good starting point for further metabolic engineering to achieve the industrial production of GlcNAc by a generally regarded as safe strain.