WASHINGTON AP – Federal regulators have undertaken an informal investigation in the anonymous online postings of John Mackey, the chief executive of Whole Foods Market Inc., some of which denigrated a smaller rival grocery chain and that raise novel questions for securities watchdogs.

Mackey’s postings over seven years on Internet financial forums, cloaked under the name “rahodeb,” at times attacked Wild Oats Markets Inc., calling its stock overpriced and predicting it would fall into bankruptcy and then be sold after its shares dipped below $5. Whole Foods announced in February that it would buy Wild Oats for around $565 million, or $18.50 a share.