A novel screening system for secretion of heterologous proteins in Bacillus subtilis

High-level production of secretory proteins in Bacillus subtilis leads to a stress response involving the two-component system CssRS and its target genes htrA and htrB. Here, we used this sensing system in a reporter strain in which gfp is under control of P-htrA, the secretion stress responsive promoter of htrA. Overexpression of heterologous secretory proteins in this strain results in green fluorescent cells, which can be separated from non-secreting, low fluorescent cells using a fluorescence-activated cell sorter (FACS). Using this principle, genomic libraries of uncharacterized prokaryotic organisms, expressed in the reporter strain, can be screened for genes encoding secretory proteins.