  Under prolonged starvation, the nucleoid of E. coli bacteria forms
nanocrystalline complexes with the protein Dps. By one hypothesis, this effect
is considered to be a manifestation of a general strategy of self-preservation
of living organisms under adverse conditions by forming stable ordered
structures which do not require consumption of energy for maintaining the
order. The effect of nucleoid biocrystallization in starved bacteria has been
investigated in a number of studies using electron microscopy. However, this
method did not answer all questions regarding the structure of the
nanocrystals, and, primarily, the question of the true conformation of DNA in
these complexes. This issue is particularly important because it is related to
a more general, actively researched topic of organization of the genetic
material, which affects gene expression and is thus critical for the
functioning of organisms. The intracellular DNA-Dps nanocrystals have the size
in the range of hundreds of nanometers and are thus particularly suitable for
study at X-ray free electron lasers (XFELs). In this paper, we discuss the
possible configurations of XFEL experiments aimed at determining the
conformation of DNA in the DNA-Dps nanocrystals grown in vivo and in vitro, as
well as the specific features and challenges associated with this type of
sample. We conclude that the XFEL technique has a high potential for uncovering
the structural details of bacterial nucleoid restructuring under stress.
