Mo. Rev. Stat. § 54.080

The county commission, at any semiannual settlement with such treasurer, or at any other time, may, if his bond be deemed insufficient, order him to give a new bond or additional security; and if such new bond or additional security be not given within twenty days after a copy of such order has been served on the treasurer, his office shall thereby become vacant, and suit may be forthwith begun on the official bond of such officer for any breach thereof.