Figure 4. TBDR7 modulated the HSAF production in L. enzymogenes.

(A) RT-PCR assay velidated the transcription of TBDR7 in the corresponding transformed strain. The size of expected DNA fragment was 388 bp. The gene, 16S rRNA (abbreviation for 16s) was used as an internal control, as described previously²². (B) Quantification of the HSAF level from the complemented strain of the TBDR7 deletion mutant. (C) Growth curves of the wild type and TBDR7 mutant in 1/10 TSB medium. (D) Mutation of TBDR7 almost entirely shut down the transcription of the key HSAF biosynthetic gene, hsaf pks/nrps. OH11, the wild-type strain of L. enzymogenes; ΔTBDR7, the TBDR7 mutant; ΔTBDR7 (pBBR), ΔTBDR7 containing an empty vector; ΔTBDR7 (TBDR7), the complemented strain of ΔTBDR7; ΔTBDR7 (TBDR7-V74A), ΔTBDR7 containing the plasmid-born TBDR7, where the amino acid Val74 within the TonB-box region was substituted by Ala74. Three replicates for each treatment were used, and the experiment was repeated three times. Vertical bars represent standard errors. The asterisk above the bars indicate a significant difference between the wild-type strain OH11 and the tested strains (*p < 0.05).