Before entering upon the duties of office, each of the commissioners shall take and subscribe to the oath of office prescribed in the Constitution of Nebraska and shall, in addition thereto, swear that he or she is not directly or indirectly interested in any common carrier or jurisdictional utility, subject to the provisions of Chapter 75, nor in the bonds, stock, mortgages, securities, contracts, or earnings of any such common carrier or jurisdictional utility, and that he or she will, to the best of his or her ability, faithfully and justly execute and enforce the duties devolving upon him or her as such commissioner, which oath shall be filed with the Secretary of State.