Section 44. A city or town having a sinking fund as provided in section forty-seven of chapter forty-four shall elect each year for terms of three years the number of sinking fund commissioners equal to the number whose term then expires. In towns they shall be elected by ballot at town meeting, and in cities by concurrent vote of both branches of the city council. In case of a vacancy the remaining member or members shall exercise the powers of the board until the vacancy is filled. The city or town treasurer shall not be eligible as a commissioner, and the acceptance by a commissioner of the office of treasurer shall render his former office vacant. The foregoing provisions as to the mode of electing commissioners shall not apply to boards of sinking fund commissioners which were established before the thirteenth day of June in the year eighteen hundred and seventy-five. The commissioners shall choose a treasurer, who may be the city or town treasurer; and if the city or town treasurer is chosen his bond shall apply to and include duties performed as treasurer of the sinking fund. If any other person is chosen treasurer he shall give a bond, with sureties, to the satisfaction of the commissioners, for the proper performance of his official duties. The commissioners may also choose a secretary.