Objective   Biological functions of the regulatory protein ompR in the two component EnvZ/OmpR system, including prodigiosin-producing ability and other biological characteristics, of Serratia marcescens FZSF02 were studied.

  Methods   Homologous recombination was used to construct ompR-knockout S. marcescens FZSF02. Effect of OmpR on the prodigiosin-producing ability was examined by LB agar plate incubation and qPCR. Methods of crystal violet staining, agar plate incubation, and others were applied to determine the biofilm-forming, mobility, and stress adaptation abilities of the transcription factor protein under various environmental stresses.

  Results   OmpR was a protein with high conserved amino acid sequences. An ompR- deleted strain, FZSF02 ∆ompR, was successfully obtained by homologous recombination and confirmed by PCR. As a result, FZSF02 ∆ompR lost prodigiosin-producing ability that possessed by the wild strain. The transcriptional levels of pigA, pigF, and pigN of the prodigiosin biosynthesis gene cluster in FZSF02 ∆ompR were respectively 3.8%, 2.0% and 2.1% of the wild type strain. The biofilm formation of FZSF02 ∆ompR declined 37.5% (at 37 ℃) and 15.1% (at 27 ℃) from its wild counterpart. On the other hand, OmpR exhibited no significant effect on the growth, mobility, or response to the environmental stress.

  Conclusion   OmpR was a newly reported gene that specifically regulated the prodigiosin biosynthesis in S. marcescens. It also significantly affected the biofilm formation but not on the growth, mobility, or stress response.