Meetings shall be held at the call of the chairman or whenever two commissioners so request. Four commissioners of the authority shall constitute a quorum, and any action taken by the authority under the provisions of sections 348.005 to 348.180 may be authorized by resolution approved by a majority, but not less than four, of the commissioners present at any regular or special meeting. No vacancy in the membership of the authority shall impair the right of a quorum to exercise all the rights and perform all the duties of the authority.