[support] Restrict posting of comments

I am running a college newspaper site and have several user roles established including ones for Section Editors and Copy Editors.

I would like to restrict the Section Editors and Copy Editors roles from posting comments on that site. I can find no way to do this, since these users are also a member of Authenticated Users which includes a broader base of users who should have the ability of posting comments...other than creating a new role for regular users (which I am unsure how to make this the default role for new users), is there a way to restrict the Section Editors and Copy Editors from posting comments?

Thanks!