Winklhofer, Michael; Abracado, Leida G.; Davila, Alfonso F.; Keim, Carolina N.; Barros, Henrique G. P. Lins de
Magnetic optimization in a multicellular magnetotactic organism.
In: Biophysical Journal, Vol. 92, No. 2: pp. 661-670
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Unicellular magnetotactic prokaryotes, which typically carry a naturalremanent magnetic moment equal to the saturation magnetic moment, arethe prime example of magnetically optimized organisms. We here reportmagnetic measurements on a multicellular magnetotactic prokaryote (MMP)consisting of 17 undifferentiated cells (mean from 148 MMPs) with chainsof ferrimagnetic particles in each cell. To test if the chain polaritiesof each cell contribute coherently to the total magnetic moment of theMMP, we used a highly sensitive magnetization measurement technique (1fAm(2)) that enabled us to determine the degree of magnetic optimization(DMO) of individual MMPs in vivo. We obtained DMO values consistentlyabove 80\%. Numerical modeling shows that the probability of reaching aDMO > 80\% would be as low as 0.017 for 17 randomly oriented magneticdipoles. We simulated different scenarios to test whether high DMOs areattainable by aggregation or self-organization of individual magneticcells. None of the scenarios investigated is likely to yieldconsistently high DMOs in each generation of MMPs. The observed high DMOvalues require strong Darwinian selection and a sophisticatedreproduction mechanism. We suggest a multicellular life cycle as themost plausible scenario for transmitting the high DMO from onegeneration to the next.