A construction of critical GJMS operators using Wodzicki's residue
  For an even dimensional, compact, conformal manifold without boundary we construct a conformally invariant differential operator of order the dimension of the manifold. In the conformally flat case, this operator coincides with the critical {\sf GJMS} operator of Graham-Jenne-Mason-Sparling. We use the Wodzicki residue of a pseudo-differential operator of order $-2,$ originally defined by A. Connes, acting on middle dimension forms. 
William J. Ugalde