Phytase production by high cell density culture of recombinant Bacillus subtilis

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Bacillus subtilis BD170, harboring a plasmid pGT44[phyC] carrying the phytase gene (phyC) and a phosphate-depletion inducible pst-promoter, was grown in a 2 l bioreactor. Using a controlled feeding of glucose, high cell densities of 32 and 56 g dry cell weight l-1 were achieved with peptone and yeast extract, respectively, as the complex nitrogen sources in a semi-defined growth medium. The fed-batch protocol was applied to production of recombinant phytase and a high extracellular phytase activity (48 U ml-1) was reached with peptone. Although the yeast extract feeding resulted in a higher cell density, it was unsuitable as a medium component for phytase expression due to its relatively high phosphate content.

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