Affiliation:
1. Department of Microbiology and Immunology, School of Medicine, Emory University, Atlanta, Georgia 30322
Abstract
ABSTRACT
Endospores of
Bacillus subtilis
are enclosed in a proteinaceous coat which can be differentiated into a thick, striated outer layer and a thinner, lamellar inner layer. We found that the N-terminal sequence of a 25-kDa protein present in a preparation of spore coat proteins matched that of the Mn-dependent superoxide dismutase (SOD) encoded by the
sodA
locus.
sodA
is transcribed throughout the growth and sporulation of a wild-type strain and is responsible for the SOD activity detected in total cell extracts prepared from
B. subtilis
. Disruption of the
sodA
locus produced a mutant that lacked any detectable SOD activity during vegetative growth and sporulation. The
sodA
mutant was not impaired in the ability to form heat- or lysozyme-resistant spores. However, examination of the coat layers of
sodA
mutant spores revealed increased extractability of the tyrosine-rich outer coat protein CotG. We showed that this condition was not accompanied by augmented transcription of the
cotG
gene in sporulating cells of the
sodA
mutant. We conclude that SodA is required for the assembly of CotG into the insoluble matrix of the spore and suggest that CotG is covalently cross-linked into the insoluble matrix by an oxidative reaction dependent on SodA. Ultrastructural analysis revealed that the inner coat formed by a
sodA
mutant was incomplete. Moreover, the outer coat lacked the characteristic striated appearance of wild-type spores, a pattern that was accentuated in a
cotG
mutant. These observations suggest that the SodA-dependent formation of the insoluble matrix containing CotG is largely responsible for the striated appearance of this coat layer.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
86 articles.
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