Sm. Ruzal et al., OSMOTIC STRENGTH BLOCKS SPORULATION AT STAGE-II BY IMPEDING ACTIVATION OF EARLY SIGMA-FACTORS IN BACILLUS-SUBTILIS, Current microbiology, 36(2), 1998, pp. 75-79
In Bacillus subtilis, osmotolerance is a stationary phase-dependent, a
daptive response inhibiting sporulation and sharing common regulators
with this process. The extent of this inhibition was determined by mea
suring transcription activity of promoter lacZ fusions to early sigma
genes (spoIIG and spoIIA coding for precursors of sigma(E) and sigma(F
)) and to reporters of them (spoIID, spoIIQ and spoIIIG), in the absen
ce and presence of 0.6 M or 1 M NaCl. The transcription activity of th
ese sigma precursors, normally occurring at the onset of the stationar
y phase, was reduced to 30-50% of their maximal expression in hyperosm
otic conditions; expression of genes under their control was, however,
more inhibited (< 10%). Therefore, sporulation was blocked at the sig
ma sigma(E) and sigma(F) activation steps. This assumption was confirm
ed by electron microscopic examinations of hyperosmotic cultures, whic
h presented asymmetric septa characteristic of stage II mutants. Discu
ssion was focused on the particular composition and/or structure of me
mbranes during hyperosmotic growth and their involvement in the arrest
of sporulation.