In any municipality having a population of less than ten thousand (10,000) according to the latest available federal census, it shall be discretionary with the governing authorities of the municipality as to whether or not a municipal judge or a prosecuting attorney, or both, shall be appointed. If the authorities of any municipality having a population of less than twenty thousand (20,000) according to the latest available federal census appoint a municipal judge, he shall be an attorney licensed in the State of Mississippi or a justice court judge of the county in which the municipality is located. The mayor or mayor pro tempore shall not serve as a municipal judge.