Zikula Community

I recently set PostNuke up for a main website and 2 subdomains. I installed PostNuke into the main website then the subs and set each one to use a seprate database (made sense to me for each to be seprate) I noticed afterwards that the sub doamins (subdomain.maindomain.net if it matters) dont have the user data that the main one does. I'm assuming that since they are one seprate databases that explains why the user data isn't being shared.
Question is can it be shared or do i have to set each sub domain to use the main database.