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J. Bacteriol., Jun 1996, 3517-3530, Vol 178, No. 12
LG van Waasbergen, M Hildebrand and BM Tebo
The marine Bacillus sp. strain SG-1 forms spores that oxidize manganese(II)
as a result of the activities of uncharacterized components of its spore
coat. Nucleotide sequence analysis of chromosomal loci previously
identified through insertion mutagenesis as being involved in manganese
oxidation identified seven possible genes (designated mnxA to mnxG) in what
appears to be an operon. A potential recognition site for the sporulation,
mother-cell-specific, RNA polymerase sigma factor, sigmaK, was located just
upstream of the cluster, and correspondingly, measurement of
beta-galactosidase activity from a Tn917-lacZ insertion in mnxD showed
expression at mid- sporulation to late sporulation (approximately stage IV
to V of sporulation). Spores of nonoxidizing mutants appeared unaffected
with respect to their temperature and chemical resistance properties and
germination characteristics. However, transmission electron microscopy
revealed alterations in the outermost spore coat. This suggests that
products of these genes may be involved in the deposition of the spore coat
structure and/or are spore coat proteins themselves. Regions of the deduced
protein product of mnxG showed amino acid sequence similarity to the family
of multicopper oxidases, a diverse group of proteins that use multiple
copper ions to oxidize a variety of substrates. Similar regions included
those that are involved in binding of copper, and the addition of copper at
a low concentration was found to enhance manganese oxidation by the spores.
This suggests that the product of this gene may function like a copper
oxidase and that it may be directly responsible for the oxidation of
manganese by the spores.
Copyright © 1996, American Society for Microbiology
Identification and characterization of a gene cluster involved in manganese oxidation by spores of the marine Bacillus sp. strain SG-1
Marine Biology Research Division and Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla 92093-0202, USA.
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