biosensing with magnetotacticbacteria
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Biosensing with magnetotacticbacteria. Match with several ideas.

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match with several ideas
Match with several ideas

2) « Bacteria as a diagnostics tool for still uncurable diseases: sensor for a molecule/hormone/... specific of a disease, and would then release a substance which could create a visible phenotype: could allow early detection of diseases (ideally) (Gabriela) »

8)  ”Create a biosensor for CO (carbon monoxyde), that would turn red or green if the threshold of toxic CO is reached. Use of dried E. coli cells and a GFP cassette : an inducible promoter sensitive to CO and then the GFP gene so that the E. coli cells would turn green if there is too much CO. This could be then detect and associated with some sort of an alarm. (Caroline)”

10) « An application in personal medicine : some treatements are efficient in patient with a certain allele while it has no effect (or an adverse response) in the patients with the other allele. An alternative to sequencing every patient would be to engineer some cells so they bind to the receptor of the drug, and would fluoresce only if not bound. Use of an inducible promoter to make the control (all cells fluoresce at the beginning and when we add the ligand no more fluorescence if it is bound). (Caroline) »

which spiece strain
Which spiece?/strain?
  • Magnetospirillum magneticum
  • Strains : AMB-1or MGT-1
  • « They are capable of growing under both microaerobic and aerobic conditions in liquid or (DeLong et al. 1993; Meldrum et al. 1993b), which makes them ideal candidates for genetic manipulation ( Matsunaga et al. 1992). » Arakaki et al, 2008
general idea
General idea

Definition of the substrate will define which receptor to use!!!

Any idea??????

Specific receptor (ABC Transporter) for the ligand of interest OR protein (type MHC protein f.ex) that carry a given ligand => *

  • Turn on magnetosome formation:
  • Produce an inhibitor of the inhibitor for a crutial protein in the magnetosome formation pathway
  • Turn on a crutial gene in the magnetosome formation pathway

Signaling cascade

Magnetosome formation

Plasmid expressing constitutively LacZ => blue cells

and expressing constitutively the receptor (ABC transporter & other genes maybe)

* In presence of a given cell type with a given allele of a receptor if the drug bind to the receptor => gene activation => positive read out, if drug doesn’t bind => negative read out

cell receptors instead of a ligand
Cell receptors instead of a ligand

If cells coming from a patient have the receptor for a given drug, Magnetobacteria will respond.

=>so the patient have the good allele for this drug

If cells coming from a patient doesn’t have the receptor for a given drug,

bacteria doesn't respond.

=> The patient haven’t the correct allele to be treated with this given drug

Cell that have a given allele for the drug receptor


Drug presenting receptor (MHC like receptor)


Signaling cascade and turning on magnetosome formation

how turning on magnetosome formation two putative targets
How turning on magnetosome formation: two putative targets

Fig. Arakaki et al, 2008

  • Two options:
  • Inhibition of MagA or MamJ inhibitor (to be found)
  • Homologous recombination of MagA or MamJ
1 inhibition of inhibition
1) Inhibition of inhibition

MagA/MamJ inhibitor

Input: binding on the receptor (ABC transporter


Inhibitor of MagA/MamJ inhibitor


Inducible promoter

Magnetite/vesicles can be formed


To be found:

MagA or Mamj inhibitor => this will then determine which protein will be transfected in the bacteria

Gene that codes for a protein (that produces/which is) an inhibitor for MagA/MamJ inhibitor

2 homologous recombination based on the single strand invasion model
2) Homologous recombination (based on the “single-strand invasion model”)
  • Steps:
  • Put MagA/MamJ gene with inducible promoter in front (a resistance to kill bacteria that haven’t integrated DNA, and a toxin to kill bacteria that have randomly integrated DNA => no recomb. bact. Are killed) in a plasmid.
  • Put this plasmid in the bacteria
  • - Select the recombined strain

2 homologous recombination genetic circuit
2) Homologous recombination (Genetic circuit)

In this recombined strain, under normal conditions MagA/MamJ is not expressed.

Once the ligand bind, MagA/MamJ is expressed -> turn on magnetite/vesicles formation -> bacterial response.

Input: binding on the receptor (ABC transporter


Magnetite/vesicles can be formed

Inducible promoter

MagA/MamJ gene

Recombined genomic bacterial DNA

MagA/MamJ protein

abc transporter
ABC transporter


Signaling cascade to turn on genes

Oldham, M.L., Davidson, A.L., Vhen, J. (2008) Structural insights into ABC transporter mechanisms. Curr. Opin. Struct. Biol. 18(6): 726-733 PMID:18948194.

Two options:

- the substrate induces promoter

- The signaling cascade induces promoter (this cascade may be changed a little bit)

link between the receptor abc transporter and gene turning on
Link between the receptor (ABC transporter) and gene turning on

Signaling cascade:

The ligand that will be used will define the ABC transporter (or another kind of transporter) and the signaling cascade we can use/modify to transmit signal.

!!! If the bacteria already have the receptor (ABC transporter), we just have to make the inducible promoter respond to a specific component of this given receptor signaling cascade. !!!

magnetisation of a magnet
Magnetisation of a magnet

Initial magnet



magnetite in bacteria
Magnetite in Bacteria

Fe3O4 or Fe3S4 cristal

Single domain, like a magnet

But the particle are so small that in the bacteria the magnetite are not coherent (the bacteria can’t be considered like a magnet). The thermal agitation move the direction of the magnetisation.

10-150 nm

The sum of magnetite can be considered like soft magnetic material (small hysteresis)

Characteristic : χr

read out 1
Read out(1)

Grouping of the bacteria in a given homogeneous magnetic field

Optimized boxes containing bacteria

Uniformly spread bacteria


Bacteria form a spot in the center once they have turned on “magnetosomal” genes

“By default” read out, bacteria are spread

No ligand sensed

Ligand sensed

read out 11
Read out(1’)

Bacteria will move to where the magnetic flux is the most important.

A coil or a magnet

The goal is to have a gradient of the magnetic field in the sample

read out 2
Read out(2)

Ferromagnetic material

whith a section S

Measurement of the coil inductance

(with N spires)



read out 21
Read out(2)

Initial inductance (without magnetite) :

L0 = N² ΛΛ = μ0 S / δ

If we have a Volume Vb of magnetite in samples’ volume

Χequ = Vb / Vsample · Χmagnetite

L = L0 · (1 + Χequ)

r equired components for the read out
Required components for the read out
  • Read out 1 :
  • Self inductance or a magnet
  • But the system should be large enough
  • The number of bacteria define the sensitivity of the system
  • Read out 2 :
  • Self inductance, magnetic circuit and a small volume for the sample
  • Electrical circuit to mesure the inductance
  • To have a good sensitivity, we need to work in small scale
  • The system is dependent of the number of bacteria
rapid and low cost
Rapid and low cost
  • Fluorescence -----> detection material=too expensive, BUT

here LacZ -----> blue color => Nothing to measure

=> Cheap (the only thing that will cost is maintaining bacteria)

=> Electronic material ---> cheap

  • Formation of vesicles --> 15min first immature vesicles (Staniland et al, 2007) => rapid

(further goal: optimize vesicles formation to observe the shape in 5 min?)


further applications
Further applications
  • Different strains with different ABC transporters can be engineered => large scale screening

(?) Maybe set of XXX-well plate with XXX different molecules that can be sensed.

=> Large scale diagnosis with rapid and easy read out.

----> In case of “allele tracking” : can screen for many alleles (=> receptor-drug binding) in on XXX-well plate

  • Can be used in medical context as well as in screening for detox context
  • ABC transporters (but with a library of mutated transporters ---> can be unlimited)
  • Ligands maybe not possible for an infinite ligand set.
  • Magnetobacterial genome not extremely well known
uniprot kegg
Uniprot - Kegg
  • MagA:
  • MagA:
  • MagA:
  • MamJ :