Background: A promoter that drives high-level, long-term expression of the target gene under substrate limited\ngrowth conditions in the absence of an artificial inducer would facilitate the efficient production of heterologous\nproteins at low cost. A novel phosphate-regulated expression system was constructed using the promoter of the\nphytase encoding gene phyL from Bacillus licheniformis for the overexpression of proteins in this industrially relevant\nhost.\nResults: It is shown that the phyL promoter enables a strong overexpression of the heterologous genes amyE and\nxynA in B. licheniformis when cells were subjected to phosphate limitation. Whether B. licheniformis can use phytate\nas an alternative phosphate source and how this substrate influences the PphyL controlled gene expression under\ngrowth conditions with limited inorganic phosphate concentrations were also investigated. It is shown that B.\nlicheniformis cells are able to use sodium phytate as alternative phosphate source. The addition of small amounts of\nsodium phytate (....) to the growth medium resulted in a strong induction and overexpression of both model\ngenes in B. licheniformis cells under phosphate limited growth conditions.\nConclusions: The PphyL controlled expression of the investigated heterologous genes in B. licheniformis is strongly\nauto-induced under phosphate limited conditions. The proposed PphyL expression system enables an\noverexpression of target genes in B. licheniformis under growth conditions, which can be easily performed in a\nfed-batch fermentation process.
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