FIG. 1.
Saturation of the secretion apparatus of B. subtilis by overexpressing AmyQ. (A) IH7441 (Pxyn-amyQ) was grown in modified 2× L broth up to a cell density of Klett 100, at which point amyQ gene expression was induced by adding xylose (concentrations were as indicated). After 1 h of induction, cell and medium fractions were separated and AmyQ in the fractions was analyzed by ECL immunoblotting. Cell samples corresponding to the indicated volumes of culture and medium samples corresponding to 10 μl of culture were immunoblotted. Precursor (p) and mature (m) forms of AmyQ are indicated by arrows. (B) The protein bands in panel A were quantified by optical scanning. For quantitation of the cell-associated mature AmyQ in cultures containing 0.16 or 0.2% xylose, another immunoblot with higher sample volumes was used. Columns show the content of secreted (white), cell-associated mature (light grey), and precursor (dark grey) forms of AmyQ in the cultures. (C) Accumulation of AmyQ in the culture medium of IH7441 (bars) induced with 0.04% xylose and specific secretion rate (line). The horizontal axis shows time after Klett 100.