Merging multiple databases on one blog

I have a multi-user blog (not MU but multiple authors) located at https://www.glasscityconnect.com and while doing some long overdue site maintenance I realized that I am somehow running this blog using 3 different databases. The site hasn’t slowed down much nor has it shown any serious quirks however is there any way to safely merge these databases into 1 to make the blog run more efficiently?