PROTEIN SECRETION IN PHOSPHATE-LIMITED CULTURES OF BACILLUS-SUBTILIS-168

The secretion of proteins from Bacillus subtilis was studied under phy siologically well-defined conditions in continuous cultures at a range of specific growth rates. The kinetics of secretion was analysed by u sing pulse-chase and immunoprecipitation techniques that allowed both processing and release to be monitored. Growth conditions were selecte d that were known to lead to significant changes in the anionic polyme r composition of the cell wall. Under magnesium limitation only low le vels of native proteins were released into the growth medium. In contr ast, much higher amounts of released protein were observed under phosp hate limitation. Although synthesis of native secretory proteins appea red to be highly regulated. only minor changes in the secretion of het erologous proteins were detected. Comparable kinetics of protein relea se of cells grown under different conditions indicated similar cell wa ll permeabilities. The large changes in the amounts of released protei ns were not reflected in the production of chaperones and components r equired for protein secretion. The data suggest that the capacity of t he secretion machinery is not a major limiting step in the export of n ative secretory proteins.