Fig. 3

Proposed diagram of Opp regulation of surfactin synthesis. Opp mediates the uptake of peptides, such as PhrA, PhrC and unknown peptides as a nutrient source. The acquisition of peptides indirectly influences comA, ccpA and degU gene expression through an unknown mechanism, which may activate surfactin synthesis gene expression. GRP, global regulator protein, Black arrows, putative regulatory effects, Black arrows with question mark, unclear or indirect effects