Avermectin production, growth, and morphological differentiation of S. avermitilis WT and sufR-related mutant strains. (A) Avermectin production of the WT, DsufR, and CsufR cultured in FM-I for 10 days. ***, P < 0.001; NS, not significant (Student’s t test). (B) Growth curves of the WT, DsufR, and CsufR in soluble FM-II. (C) SEM images showing morphological development of the WT, DsufR, and CsufR grown for 2 or 6 days on SFM media. Error bars, standard deviation of three biological replicates.