## 3 Results and Discussion
### EMR Results  
To minimize dielectric losses from the cultivation medium, the samples in a flat cylindrical cuvette 0.15 mm high with a diameter of 20 mm, filled and sealed under nitrogen, were placed at the bottom of a balanced cylindrical resonator with the TE\({}_{111}\) microwave oscillation type used in the spectrometer [38]. EMR spectra were obtained from the suspensions of BB-1, MSR-1, and AMB-1 strains of the genus _Magnetospirillum_; the spin induction signals were recorded at room temperature. The phase of the reference voltage of the microwave detector was determined from the shape of the signal from the witness sample (nitroxyl radical). The latter was placed on the wall of the microwave cavity opposite the bottom of the resonator with the sample cuvette to avoid the contribution of the sample magnetization to the field at the place of the witness. The EMR signal proportional to the mixture of the dispersion \(\chi^{\prime\prime}yx\) - and absorption \(\chi^{\prime}yx\) parts of the magnetic susceptibility was registered as a function of the magnetic field ranging from 70 to 520 kA/m. The adjustable mixing angle was preset in the measurement and further specified in the fit procedure. The suspension of bacteria with magnetosomes, due to their random orientation, is magnetically similar to a polycrystalline ferromagnet. The optical density of the suspensions was measured to be 0.06-0.09, indicating a rather low concentration of the bacteria. Therefore, one may neglect the magnetic interactions between them and consider the bacteria ensemble within the model of independent \"grains\". In the case of conventional uniaxial magnetic anisotropy, the signal from nanoparticles of the same type is split into two peaks [47]. In our case, the original EMR signal was registered, rather than its derivative. The initial processing of the spectra consisted in subtracting the background signal from the resonator without a sample. The latter includes the Hall effect from conduction electrons of the resonator material, which are involved in the microwave currents flowing through the bottom of the resonator. Like the resonant magnetic transition in the sample, the Hall effect leads to rotation of the polarization plane of microwave oscillations in the resonator [38]. The Hall effect can also be observed in the sample if it contains charged carriers. It is known that the line shape of the signal from a polycrystalline ferromagnetic sample is not Lorentzian [47]. Therefore, for the semi-quantitative analysis of the recorded EMR spectra, the line shape of any signal was assumed to be Gaussian. Depending on the number of extrema, two, three, or four Gaussians were used at the fitting, together with the linear Hall signal. Then, for clarity, the Hall signal was subtracted from the fitted spectra. The signals for BB-1, MSR-1, and AMB-1 and their fits are presented in Figure 7. The fit parameters are shown in Table 2.  
Figure 7: Electron magnetic resonance spectra and their fits for suspensions of BB-1, MSR-1, and AMB-1 strains of the genus _Magnetospirillum_. The experimental signals and the fitting curves are presented by open circles and red lines, respectively. The Gaussians obtained at fitting include both absorption and dispersion (solid and dashed lines, respectively); their contribution to fitting curves with appropriate weights is shown below the experimental points. Referring to Table 1, magenta, blue, green and orange lines represent Gaussians 1, 2, 3, and 4, respectively. The arrows on panels (**a**,**d**) indicate the position of the residual signal from the witness (nitrosyl radical, _g_-factor = 2.0055), after subtracting the background signal from the resonator without the sample. Our previous experiments with colloidal aqueous solutions of magnetite nanoparticles in a dextran shell with the average magnetic core size 10 nm and the average magnetic moment 2.6 \(\times\) 10\({}^{4}\) u\({}_{\text{B}}\) showed the formation of MNP aggregates with the average number of MNPs 55.