All refunding bonds shall be negotiable instruments and may have coupons evidencing interest, payable at annual or semiannual periods, and shall have all the rights of security, including liens on assessments of benefits and levy of taxes on the lands, together with all remedies for their collection that are provided for the original bonds issued by a municipal improvement district and may be further secured by a pledge and mortgage of the assessment of benefits and taxes in the district, to be executed by the commissioners.