Transcript MAGNETOTACTIC BACTERIA - Home page of SAS Kosice

The main building of the institute
name: A. Džarová
subject of research:
Magnetic properties of fine magnetic nanoparticles (magnetosomes)
supervisor: Dr M. Timko
Our research interests in the section of the
magnetism:
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preparation magnetic particles :
precipitations (synthetic mag. particles)
the chemically synthesized magnetite nanoparticles (Fe3O4) for biomedical
using are covered by thin layer of biocompatible materials or are encapsulated into
biodegradable polymers
-
biomineralizations (natural mag. particles)
- a new biological magnetic particles (magnetosomes) was found as a product
of biomineralization process from magnetotactic bacteria. The encapsulation of
magnetosomes within the organic membrane provides a natural coating, which
ensures superior dispersibility of the Fe3O4 particles and provides excellent target for
immobilization biologically active substances
In my experiments magnetosomes were prepared from
MTB strain Magnetotacticum Magnetospirillum :
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MTB are microorganisms that belong to a heterogeneous
group of Gram-negative bacteria with diverse morphologies
and habitats
they are a diverse group of aquatic prokaryotes

strain AMB-1 is Gram-negative
α-proteobacterium that more
oxygen-tolerant and easier to
grow on a large scale
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MTB orient and migrate along geomagnetic field lines –
this ability is based on intracellular magnetic
structures known as –
MAGNETOSOMES
[an intracellular single-magnetic-domain crystal of a magnetic iron mineral
(the magnetite) to be enclosed by a membrane (a lipid bilayer admixed
with proteins) the membrane is intracellular and may be connected to the
cytoplasmic membrane]
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AMB-1 have single chain of magnetosomes longitudinally
traverses the cell
Process of magnetosome
formation :
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invagination of the
cytoplasmic membrane
and vesicle formation
for the magnetosome
membrane precursor
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accumulation of
ferrous/ferric ions in the
cell and the vesicles
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strictly controlled iron
oxidation–reduction
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have linear dimensions of 40 to 50 nm and are separated from adjacent
particles in the chain by approximately 4 to 10 nm
(the mean size of our magnetosomes estimated from TEM was 34 nm)
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the particles are well crystallized with truncated octahedral morphology and
are oriented so that [111] faces are perpendicular to the magnetosomes
chain axis
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the number of magnetosomes per cell is variable within a population, but
the average number is typically 10 to 20 magnetosomes per cell
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the average number of magnetosomes also varies with culture conditions,
especially chelated iron concentration and disolved oxygen tension
Biotechnological applications:
Magnetosomes can be used:
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for the nondestructive domain analysis of soft mag. material
locate magnetic poles on meteoric magnetic grains
the removal of heavy metals and radionuclides from water
the used of „Microbial magnetometer”
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a great deal of biological applications
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for example:
- a potential biomarker for geobiologists
- an ideal system for studying biomineralization
- magnetosomes have been also used for the generation of magnetic antibodies
- as components of medically important biosensors
- incorporated bacterial magnetite particles into eukaryotic cells
- have been used in DNA and RNA isolation procedures
- were also used as carriers for the introduction of DNA into cell
- as contrast agents for magnetic resonance imaging and tumor-specific drug carriers
based on intratumoral enrichment
… and in some other
In our experiment for cultivation Magnetotacticum Magnetospirillum sp.
AMB-1 we used medium consisted of (per 1 L medium):
10 mL Wolfe’s vitamin solution
5 mL Wolfe’s mineral solution
0.68 g KH2PO4
0.848 g sodium succinate hexahydrate
0.575 g sodium tartrate dihydrate
0.083 g sodium acetate trihydrate
0.225 mL 0.2% (w/v) resazurin (aqueous)
0.17 g NaNO3
0.04 g ascorbic acid
2 mL 0.01 M ferric quinate
• resazurin was added to media as colorimetric indicator of redox potential
• the pH was adjusted to 6.75 with NaOH
• this medium was prereduced under nitrogen for a period of 1 hour, using copper as a
reducing agent, and was subsequently dispensed into culture tubes in an anaerobic hood
• inoculated tubes were incubated at 25°C for a period of 4 days
Techniques for the isolation and purification of magnetosome
particles from Magnetotacticum Magnetospirillum species:
•
are based on magnetic separation or a combination of a sucrose-gradient
centrifugation and a magnetic separation technique
• these procedures leave the surrounding membrane intact and magnetosome
preparations are apparently free of contaminating material
• owing to the presence of the enveloping membrane, isolated magnetosome
particles form stable, well-dispersed suspensions
• after solubilization of the membrane by a detergent, the remaining inorganic
crystals tend to agglomerate as a result of magnetic attractive forces
• typically, 2.6 mg bacterial magnetite can be
derived from a 1000-mL culture of
Magnetospirillum sp. AMB-1. for the
isolation of the magnetosome particles,
we have used the method described by Gorby
MAGNETOSOMES:
The prepared magnetosomes in our laboratory were examined by
TEM and magnetic measurement
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comprise nanometer –sized, membrane-bound crystals
(bacterial magnetic particles) of the magnetic iron minerals magnetite
(Fe3O4)
electron micrograph of the magnetosomes reveals that magnetosomes
dispersed very well are arranged in bent chains which tend to form closed
loops in suspension so as to minimize their magnetic stray field energy
the mean diameter is estimated to be 34 nm
Magnetic properties were examined by SQUID
magnetometer Quantum Design:
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the saturation magnetization of the magnetosomes was estimated to
be 62 emu/g what is smaller than for chemically synthetized
magnetite 75 emu/g at room temperature due to presence of
nonmagnetic organic layer
80
60
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the curve of field dependence
of magnetization at 293 K
exhibited the remanence
of 21 emu/g
MAgnetization [emu/g]
40
20
0
-20
-40
-60
-80
-15000
-10000
-5000
0
5000
10000
15000
MAgnetic field [Oe]
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coercivity of 185 Oe what is connected with fact that the mean
diameter (34 nm) is larger than critical size for transition from
superparamagnetic to ferrimagnetic behaviour
20000
PRESENTATION
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Budapest, Hungary: 4th Central European
Training School on Neutron Scattering
FORMATION AND MAGNETIC PROPERTIES OF MAGNETOSOMES
A. Džarová, M. Timko, A. Šprincová, P. Kopčanský, J. Kováč, M. Koneracká, I. Vávra
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Leiden, Netherland: Magnetic
Nanoparticles: Challenges and Future
Prospects
Thank you for your attention