Affiliation:
1. Ludwig-Maximilians-Universität München, Departement Biologie I, Mikrobiologie, LMU Biozentrum, Planegg Martinsried, Germany
2. University of Pannonia, Department of Earth and Environmental Sciences, Veszprém, Hungary
3. Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Potsdam, Germany
Abstract
ABSTRACT
Biosynthesis of bacterial magnetosomes, which are intracellular membrane-enclosed, nanosized magnetic crystals, is controlled by a set of >30 specific genes. In
Magnetospirillum gryphiswaldense
, these are clustered mostly within a large conserved genomic magnetosome island (MAI) comprising the
mms6
,
mamGFDC
,
mamAB
, and
mamXY
operons. Here, we demonstrate that the five previously uncharacterized genes of the
mms6
operon have crucial functions in the regulation of magnetosome biomineralization that partially overlap MamF and other proteins encoded by the adjacent
mamGFDC
operon. While all other deletions resulted in size reduction, elimination of either
mms36
or
mms48
caused the synthesis of magnetite crystals larger than those in the wild type (WT). Whereas the
mms6
operon encodes accessory factors for crystal maturation, the large
mamAB
operon contains several essential and nonessential genes involved in various other steps of magnetosome biosynthesis, as shown by single deletions of all
mamAB
genes. While single deletions of
mamL
, -
P
, -
Q
, -
R
, -
B
, -
S
, -
T
, and -
U
showed phenotypes similar to those of their orthologs in a previous study in the related
M. magneticum
, we found
mamI
and
mamN
to be not required for at least rudimentary iron biomineralization in
M. gryphiswaldense
. Thus, only
mamE
, -
L
, -
M
, -
O
, -
Q
, and -
B
were essential for formation of magnetite, whereas a
mamI
mutant still biomineralized tiny particles which, however, consisted of the nonmagnetic iron oxide hematite, as shown by high-resolution transmission electron microscopy (HRTEM) and the X-ray absorption near-edge structure (XANES). Based on this and previous studies, we propose an extended model for magnetosome biosynthesis in
M. gryphiswaldense
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology