HR: 1340h
AN: B33B-0259 [Abstracts]
TI: Genes Necessary for Bacterial Magnetite Biomineralization Identified by Transposon
Mutagenesis
AU: * Nash, C Z
EM: cody@caltech.edu
AF: California Institute of Technology, Department of Geological and Planetary Sciences, MC 170-25,
Pasadena, CA 91125
United States
AU: Komeili, A
EM: komeili@gps.caltech.edu
AF: California Institute of Technology, Department of Geological and Planetary Sciences, MC 170-25,
Pasadena, CA 91125
United States
AU: Newman, D K
EM: dkn@gps.caltech.edu
AF: California Institute of Technology, Department of Geological and Planetary Sciences, MC 170-25,
Pasadena, CA 91125
United States
AU: Kirschvink, J L
EM: kirschvink@caltech.edu
AF: California Institute of Technology, Department of Geological and Planetary Sciences, MC 170-25,
Pasadena, CA 91125
United States
AB:
Magnetic bacteria synthesize nanoscale crystals of magnetite in intracellular, membrane-bounded organelles (magnetosomes).
These crystals are preserved in the fossil record at least as far back as the late Neoproterozoic and have been tentatively
identified in much older rocks {\it (1)}. This fossil record may provide deep time calibration points for molecular evolution
studies once the genes involved in biologically controlled magnetic mineralization (BCMM) are known. Further, a genetic and
biochemical understanding of BCMM will give insight into the depositional environment and biogeochemical cycles in which
magnetic bacteria play a role.
The BCMM process is not well understood, though proteins have been identified from the magnetosome membrane and genetic
manipulation and biochemical characterization of these proteins are underway. Most of the proteins currently thought to be
involved are encoded within the {\it mam} cluster, a large cluster of genes whose products localize to the magnetosome
membrane and are conserved among magnetic bacteria {\it (2)}.
In an effort to identify all of the genes necessary for bacterial BCMM, we undertook a transposon mutagenesis of {\it
Magnetospirillum magneticum} AMB-1. Non-magnetic mutants (MNMs) were identified by growth in liquid culture followed by a
magnetic assay. The insertion site of the transposon was identified two ways. First MNMs were screened with a PCR assay to
determine if the transposon had inserted into the {\it mam} cluster. Second, the transposon was rescued from the mutant DNA
and cloned for sequencing. The majority insertion sites are located within the {\it mam} cluster. Insertion sites also occur
in operons which have not previously been suspected to be involved in magnetite biomineralization. None of the insertion
sites have occurred within genes reported from previous transposon mutagenesis studies of AMB-1 {\it (3, 4)}. Two of the
non-{\it mam} cluster insertion sites occur in operons containing genes conserved particularly between MS-1 and MC-1. We are
undertaking a complementation strategy to demonstrate the necessity of these novel genes in BCMM as well as characterizing
the phenotypes of the mutants.
1. S. B. R. Chang, J. F. Stolz, J. L. Kirschvink, S. M. Awramik, Precambrian Res. 43, 305-315 (1989).
2. K. Grnberg, C. Wawer, B. M. Tebo, D. Schler, Appl. Environ. Microbiol. 67, 4573-4582 (2001).
3. A. T. Wahyudi, H. Takeyama, T. Matsunaga, Appl. Biochem. Biotechnol. 91-3, 147-154 (2001).
4. T. Matsunaga, C. Nakamura, J. G. Burgess, K. Sode, J. Bacteriol. 174, 2748-2753 (1992).
DE: 4840 Microbiology
DE: 4803 Bacteria
DE: 1505 Biomagnetism
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting