Section 6. Upon the expiration of the term of office of a commissioner, his successor shall be appointed by the governor for a term coterminous with that of the governor, and shall serve at the pleasure of the governor. The position of commissioner shall be classified in accordance with section forty-five of chapter thirty and the salary shall be determined in accordance with section forty-six C of said chapter thirty and shall devote full time during business hours to the duties of his office. He shall give bond with sureties in the sum of ten thousand dollars, to be approved by the state treasurer, for the faithful performance of his duties.