Journal of Bacteriology, March 2001, p. 1881-1890, Vol. 183, No. 6
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.6.1881-1890.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
-Amylase in
Bacillus subtilis


Vaccine Development Laboratory, National Public Health Institute, FIN-00300 Helsinki, Finland
Received 18 September 2000/Accepted 6 December 2000
Regulated expression of AmyQ
-amylase of Bacillus
amyloliquefaciens was used to examine the capacity of the protein
secretion apparatus of B. subtilis. One B. subtilis cell was found to secrete maximally 10 fg of AmyQ per h.
The signal peptidase SipT limits the rate of processing of the signal
peptide. Another limit is set by PrsA lipoprotein. The wild-type level
of PrsA was found to be 2 × 104 molecules per cell.
Decreasing the cellular level of PrsA did not decrease the capacity of
the protein translocation or signal peptide processing steps but
dramatically affected secretion in a posttranslocational step. There
was a linear correlation between the number of cellular PrsA
molecules and the number of secreted AmyQ molecules over a wide range
of prsA and amyQ expression levels. Significantly, even when amyQ was expressed at low levels,
overproduction of PrsA enhanced its secretion. The finding is
consistent with a reversible interaction between PrsA and AmyQ. The
high cellular level of PrsA suggests a chaperone-like function. PrsA
was also found to be essential for the viability of B. subtilis. Drastic depletion of PrsA resulted in altered
cellular morphology and ultimately in cell death.
Present address: Laboratory of Bioprocess Engineering, Helsinki
University of Technology, FIN-02015 Espoo, Finland.
Present address: Medicity Research Laboratory, University of Turku
and National Public Health Institute, FIN-20520 Turku, Finland.
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