One-to-one correspondences are established between the set of all nondegenerate graded Jacobi operators of degree $-1$ defined on the graded algebra $\Omega(M)$ of differential forms on a smooth, oriented, Riemannian manifold $M$, the space of bundle isomorphisms $L{\A}TM{\to} TM$, and the space of nondegenerate derivations of degree $1$ having null square. Derivations with this property, and Jacobi structures of odd $\Bbb Z_2$-degree are also studied through the action of the automorphism group of $\Omega(M)$.