Effect of rocG expression on AmyK38 production, secretion stress responses, and external pH. Strain R-1926 (MGB874 Pspac-rocG and PhtrB-lacZ) harboring pHYK38 was cultured in 2xL-Mal medium with shaking at 30°C in the absence (white symbols and gray bars) or presence (black symbols and black bars) of 1 mM IPTG. (A) Culture OD600 (circles) and α-amylase activities in the growth medium (bars). (B) Secretion stress levels were determined by measuring β-galactosidase activities of cells expressing a transcriptional htrB-lacZ fusion. (C) Ammonia concentrations (squares) and pH of culture broth (diamonds). (D) Concentrations of sugar in the growth media. All results presented are the averages of three individual experiments. Error bars represent standard deviations (n = 3).