A ‘Porgy’ with spirit and heart

The genius in question, of course, was George Gershwin. Fast-forward to a few weeks ago, when another composer of genius - Stephen Sondheim - created a considerable stir by firing off a scathing letter to the Times about the American Repertory Theater’s musical theater adaptation of Gershwin’s masterpiece, accusing director Diane Paulus and her collaborators of “arrogance’’ and “disdain’’ in their attitude toward “Porgy.’’

As it turns out, Sondheim needn’t have worried. The ART’s vibrant and stirring production of “The Gershwins’ Porgy and Bess’’ makes some revisions, but Paulus and adapters Suzan-Lori Parks and Dierdre L. Murray are largely faithful to the spirit and the structure of the original. And in Audra McDonald, this production boasts a Bess for the ages.

With a scar across her left cheek and a wary, wounded demeanor to match, McDonald’s Bess emerges very slowly from her shell, drawn out into the world by the unconditional love of Porgy (Norm Lewis), a disabled beggar. Their duet on “Bess, You Is My Woman Now’’ near the end of act one is a thing of beauty to watch and to hear: Lewis eases into it gently and tentatively, as if not entirely sure Bess will reciprocate, while the subtle play of expressions on McDonald’s face suggests that, mid-song, the realization has dawned on Bess that she does indeed love Porgy.

Later, when Bess pleads with Porgy not to let her former lover, Crown, take her away again in “I Loves You, Porgy,’’ McDonald brings a shattering, life-or-death urgency to the scene.

For much of the show, the gray-bearded Lewis is somewhat understated, as if he is still exploring the different dimensions of his character. But he finds Porgy’s voice fully in song, with a robust rendition of “I Got Plenty of Nothing’’ that captures Porgy’s wit, wisdom, and newfound sexual confidence.