  \textit{Magnetospirillum gryphiswaldense} biosynthesize high quality
magnetite nanoparticles, called magnetosomes, and arrange them into a chain
that behaves like a magnetic compass. Here we perform magnetometry and
polarized small-angle neutron scattering (SANS) experiments on a powder of
freeze-dried and immobilized \textit{M. gryphiswaldense}. We confirm that the
individual nanoparticles are single-domain particles and that an alignment of
the particle moments in field direction occurs exclusively by a N\'eel-like
rotation. Our magnetometry results of the bacteria powder indicate an absence
of dipolar interactions between the particle chains and a dominant uniaxial
magnetic anisotropy. Finally, we can verify by SANS that the chain structure
within the immobilized, freeze-dried bacteria is preserved also after
application of large magnetic fields of up to 1\,T.
