Alteration of gene regulation
Bacillus subtilis strain ATCC 6633 produces the lipopeptide mycosubtilin. Replacing the native promotor of the mycosubtilin operon in ATCC 6633 with a constitutive promotor yielded the recombinant strain BBG100. This recombinant produced up to 15fold more mycosubtilin and suppressed Pythium aphanidermatum on tomato significantly better than the wild type did (Leclere et al., 2005).
The two-component regulatory system consisting of GacS (sensor kinase) and GacA (response regulator) is involved in the regulation of secondary metabolism. In a second example of altered gene regulation, Ligon et al. (2000) enhanced expression of the biosynthesis genes (prnABCD) for the antibiotic pyrrolnitrin in P. fluorescens BL915 by adding additional plasmid-borne copies of gacA, by changing the first base in the coding sequence of the gacA gene to a more efficient codon, or by replacing the native promoter of gacA with the stronger Ptac promoter. Each of these alterations resulted in a marked increase in both the amount of pyrrolnitrin produced by the various genetically modified strains and their level of control of Rhizoctonia solani on cucumber and impatiens. The level of antibiotic production was directly related to the level of control of Rhizoctonia solani.