Isolation of an Escherichia coli K4 kfoC mutant over-producing capsular chondroitin

BACKGROUND Chondroitin sulphate is a complex polysaccharide having important structural and protective functions in animal tissues. Extracted from animals, this compound is used as a human anti-inflammatory drug. Among bacteria, Escherichia coli K4 produces a capsule containing a non-sulphate chondroitin and its development may provide an efficient and cheap fermentative production of the polysaccharide. RESULTS A random N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis was performed on E. coli K4 to isolate mutants showing an increased production of chondroitin. Several mutants were isolated, one of which, here named VZ15, produced about 80% more chondroitin than the wild type E. coli. We found that the mutant has a missense mutation in the codon 313 of kfoC, the gene encoding chondroitin polymerase (K4CP), with a change from arginine to glutamine. A docking analysis to explain the increased productivity of the K4CP enzyme is presented. CONCLUSION The enhanced chondroitin production by the E. coli K4 mutant reported here shows the validity of the strain improvement strategy for more cost-friendly fermentative processes in the production of this pharmaceutically important but so-far expensive polysaccharide.