Eric Shaff, chief operating and financial officer of Seres Therapeutics (NASDAQ: MCRB), has been promoted to president and CEO. Shaff is also joining the board of directors of the Cambridge, MA, microbiome drugs developer. Shaff joined Seres as chief financial officer in 2014 and last year took on the additional role of chief operating officer. He succeeds Roger Pomerantz, who will continue in his role as chairman of the Seres board. Pomerantz joined the board in 2013 and was named CEO seven months later. Lead Seres drug candidate SER-109 is in late-stage clinical studies testing it as a treatment for recurrent Clostridium difficile infection.