ABSTRACT
The Fst toxin of the Enterococcus faecalis pAD1-encoded
par addiction module functions intracellularly to kill
plasmid-free segregants. Previous results had shown that Fst induction
results in membrane permeabilization and cessation of macromolecular
synthesis, but only after 45 min. Electron micrographs of toxin-induced
cells showed no obvious membrane abnormalities but did reveal defects
in nucleoid segregation and cell division, begging the question of
which is the primary effect of Fst. To distinguish the possibilities,
division septae and nucleoids were visualized simultaneously with
fluorescent vancomycin and a variety of DNA stains. Results showed that
division and segregation defects occurred in some cells within 15 min
after induction. At these early time points, affected cells remained
resistant to membrane-impermeant DNA stains, suggesting
that loss of membrane integrity is a secondary effect caused by ongoing
division and/or segregation defects. Fst-resistant mutants showed
greater variability in cell length and formed multiple septal rings
even in the absence of Fst. Fst induction was also toxic to
Bacillus subtilis. In this species, Fst induction caused only
minor division abnormalities, but all cells showed a condensation of
the nucleoid, suggesting that effects on the structure of the
chromosomal DNA might be
paramount.
Basic Amino Acid Inhibition of Cell Division and Macromolecular Synthesis in Saccharomyces cerevisiae
