Interaction of proteins associated with the magnetosome assembly in magnetotactic bacteria as revealed by two-hybrid two-photon excitation fluorescence lifetime imaging microscopy förster resonance energy transfer

Bacteria have recently revealed an unexpectedly complex level of intracellular organization. Magnetotactic bacteria represent a unique class of such organization through the presence of their magnetosome organelles, which are organized along the magnetosome filament. Although the role of individual magnetosomes-associated proteins has started to be unraveled, their interaction has not been addressed with current state-of-the-art optical microscopy techniques, effectively leaving models of the magnetotactic bacteria protein assembly arguable. Here we report on the use of FLIM-FRET to assess the interaction of MamK (actin-like protein) and MamJ, two magnetosome membrane associated proteins essential to the assembly of magnetosomes in a chain. We used a host organism (E. coli) to express eGFP-MamJ and MamK-mCherry, the latest expectedly forming a filament. We found that in the presence of MamK the fluorescence of eGFP-MamJ is distributed along the MamK filament. FRET analysis using the fluorescence lifetime of the donor, eGFP, revealed a spatial proximity of MamK-mCherry and eGFP-MamJ typical of a stable physical interaction between two proteins. Our study effectively led to the reconstruction of part of the magnetotactic apparatus in vivo.