  Recent studies have shown that bacterial nucleoid-associated proteins (NAPs)
can bind to DNA and result in altered structural organization and bridging
interactions. Under spontaneous self-assembly, NAPs may form anisotropic
amyloid fibers, whose effects are still more significant on DNA dynamics. To
test this hypothesis, microrheology experiments on dispersions of DNA
associated with the amyloid terminal domain (CTR) of the bacterial protein Hfq
were performed using the technique of magnetic rotational spectroscopy (MRS).
In this chapter, we survey this microrheology technique which is based on the
remote actuation of magnetic wires embedded in a sample. MRS is interesting as
it is easy to implement, and does not require complex procedures regarding data
treatment. Pertaining to the interaction between DNA and amyloid fibers, it is
found that DNA and Hfq-CTR protein dispersion behave like a gel, an outcome
that suggests the formation of a network of amyloid fibers cross-linked with
the DNA strands. In contrast, the pristine DNA and Hfq-CTR dispersions behave
as purely viscous liquids. To broaden the scope of the MRS technique, we
include theoretical predictions for the rotation of magnetic wires regarding
the generic behaviors of basic rheological models from continuum mechanics, and
we list the complex fluids studied by this technique over the past 10 years.
