## 3 Results and Discussion
### NLR-M2 Results
The large error bars in the obtained parameters, especially in the saturation magnetization and the number of magnetic centers, are due, on the one hand, to a poor signal-to-noise ratio at a given scan frequency and, on the other hand, to a strong correlation of the model parameters. Note that we studied unsynchronized cell cultures in the aqueous suspension form, so the samples contained the cells at different stages of growth, including cells in the stage of division and dying cells. Thus, the ensemble of magnetosomes in the sample included the chains of magnetosomes of different sizes [17]. A contribution to the magnetic response was also made by the proteins containing iron nanoparticles, for the genetically controlled growth of the magnetosomes [44]. Unlike conventional magnetic measurements using dehydrated fixed samples, in our case of an aqueous solution, cells and magnetosomes can move and rotate. In particular, the scanning magnetic field \(H\) forces the cells with the magnetosome chain attached to the membrane to orient themselves along the field and to overturn when the field direction changes. The scan period \(1/F_{\mathrm{sc}}\) = 125 ms is too short for the complete reversal. Therefore, the extremum of the ReM\({}_{2}\)(\(H\)) signal recorded, for example, at the reverse \(H\) scan is located in the quadrant \(H\) > 0, rather than in the quadrant \(H\) < 0 as expected for symmetrical reasons (Figures 3a,d, 4a,d, 5a,d and 6d). Increasing the sweep period to 4 s allows the cells to make such an overturn, although a certain time lag from the field, manifesting itself in the \(H\) hysteresis, still remains (Figures 3b,e, 4b,e, 5b and 6b,e). A short delay is observed even for the minimal \(F_{\mathrm{sc}}\) = 0.02 Hz, which indicates that it takes time, even more than 50 s, to flip the cells. From Table 1, the magnetic moment of the \"heavy\" mode with the extremum in the weak field is, at least, several times greater than the moment of the \"light\" mode and should be attributed to the magnetosome chains fixed on the bacterial cytoskeleton. The \"heavy\" fraction also exhibits two orders of magnitude of lower saturation magnetization and the number of magnetic centers for the entire ensemble of the bacteria in the sample, compared to the \"light\" fraction. This suggests that it is energetically unfavorable for the cells to synthesize a pool of the \"heavy\" fraction of magnetosomes, due to losses in magnetostatic energy. Only one chain is synthesized in every cell [1; 2; 3; 4; 5], as illustrated by the TEM image of Figure 2. This chain is bound to the cytoskeleton to avoid its rolling up. In contrast, the \"light\" fragments are free to roll up or to couple antiferromagnetically with each other by dipolar forces to minimize their magnetostatic energy. This explains the mean magnetic moments of the \"light\" fractions being only of the order \(10^{4}\)\(\mu_{\mathrm{B}}\), corresponding to the effective NP size of less than 10 nm, which is much smaller than expected for magnetosomes [1; 2; 3; 45]. The high concentration of magnetosomes in the \"light\" fraction can be seen in the AFM image of Figure S1. This fraction with the wide distribution of magnetic moments can probably include, at least partially, nascent (immature) magnetosomes formed after the cell division, the iron-carrying proteins for synthesis, and fragments of the chains formed in dead cells after the destruction of their membranes. These structures can be expected to have significantly smaller moments than that of the magnetosome chain of mature cells. The fragments of the magnetosome chain that are not bound to the cell membrane are probably structurally compacted due to dipolar correlations of the antiferromagnetic type to decrease the magnetostatic energy, resulting in the decrease of their total magnetic moment. The \"old\" and \"new\" specimens exhibit more or less close parameters, except only \(\widetilde{M}\) for MSR-1. The parameters for SO-1 \"new\" could not be resolved.