The suffix -ista is permanent. Therefore, if we want to change the word to masculine we will not change the ‘A’ to ‘O’, but rather change the article, e.g. un taxista (a taxi driver - masculine), el taxista (the taxi driver – masculine), una taxista (a taxi driver – feminine), la taxista (the taxi driver – feminine).
The Suffix –(C)ITO/A/OS/AS
This suffix is used to indicate diminutiveness and affection.