Positively regulates the biosynthesis of andrimid, a broad-spectrum antibiotic, by activating the expression of the adm biosynthetic gene cluster (PubMed:26914969, PubMed:30500953). It specifically binds to a region within the adm promoter (PubMed:30500953). AdmX-mediated transcription is inhibited by indole-3-acetic and indole-3-pyruvic acids (PubMed:30500953). AdmX recognizes and binds the auxin indole-3-acetic acid (IAA), which causes conformational changes in AdmX that result in the inhibition of the expression of the andrimid gene cluster and the suppression of antibiotic production (PubMed:30500953). It also recognizes indole-3-pyruvic acid (IPA), an intermediate of the main IAA biosynthetic pathway in plants and plant beneficial bacteria, which also prevents andrimid synthesis, but to a much lesser extent (PubMed:30500953). Expressed in late logarithmic phase of growth. Deletion mutant does not inhibit growth of B.subtilis and shows decreased adm transcript levels. Belongs to the LysR transcriptional regulatory family.