Section 29. All contracts made by any department, board or commission where the amount involved is five thousand dollars or more shall be in writing, and no such contract shall be deemed to have been made or executed until the approval of the mayor under Plan A, B, C or F, or of the city manager under Plan D or E, and also of the officer or the head of the department or of the chairman of the board, as the case may be, making the contract is affixed thereto. Any contract made as aforesaid may be required to be accompanied by a bond with sureties satisfactory to the board or official having the matter in charge, or by a deposit of money, certified check or other security for the faithful performance thereof, and such bonds or other securities shall be deposited with the city treasurer until the contract has been carried out in all respects; and no such contract shall be altered except by a written agreement of the contractor, the sureties on his bond, if any, and the officer, department or board, as the case may be, making the contract, with the approval of the mayor under Plan A, B, C, D or F, or of the city manager under Plan E, affixed thereto. Any cash deposit or check payable to a city received as security for performance under this section may be deposited by said treasurer in any bank or trust company under a separate account to be known as a performance deposit account.

The provisions of this section shall be deemed to have been complied with on all purchases made under the provisions of sections twenty-two A and twenty-two B of chapter seven when one municipality acting on behalf of other municipalities complies with the provisions of this section, or when purchases are made from a vendor holding a contract with the commonwealth for the item or items being purchased.