Let (E, H, μ) be an abstract Wiener space and let D V := V D, where D denotes the Malliavin derivative and V is a closed and densely defined operator from H into another Hilbert space H . Given a bounded operator B on H , coercive on the range R(V ), we consider the operators A := V * BV in H and A := V V * B in H , as well as the realisations of the operators L := D * V BD V and L := D V D * V B in L p (E, μ) and L p (E, μ; H ) respectively, where 1 < p < ∞. Our main result asserts that the following four assertions are equivalent:) A admits a bounded H ∞ -functional calculus on R(V ). Moreover, if these conditions are satisfied, then D(L) = D(D 2 V ) ∩ D(D A ). The equivalence (1)-(4) is a nonsymmetric generalisation of the classical Meyer inequalities of Malliavin calculus (where H = H , V = I , B = 1 2 I ). A one-sided version of (1)-(4), giving L p -boundedness of the Riesz transform D V / √ L in terms of a square function estimate, is also obtained. As an application let −A generate an analytic C 0 -contraction ✩ 2411semigroup on a Hilbert space H and let −L be the L p -realisation of the generator of its second quantisation. Our results imply that two-sided bounds for the Riesz transform of L are equivalent with the Kato square root property for A. The boundedness of the Riesz transform is used to obtain an L p -domain characterisation for the operator L.