  Pauli Exclusion Principle (PEP) violations induced by space-time
non-commutativity, a class of universality for several models of Quantum
Gravity, are investigated by the VIP-2 Lead experiment at the Gran Sasso
underground National Laboratory of INFN. The VIP-2 Lead experimental bound on
the non-commutative space-time scale $\Lambda$ excludes $\theta$-Poincar\'e far
above the Planck scale for non vanishing ``electric-like" components of
$\theta_{\mu \nu}$, and up to $6.9 \cdot 10^{-2}$ Planck scales if they are
null. Therefore, this new bound represents the tightest one so far provided by
atomic transitions tests. This result strongly motivates high sensitivity
underground X-ray measurements as critical tests of Quantum Gravity and of the
very microscopic space-time structure.
