Prevent a profile type from starting a stream

Hi,

I have a news blog (aggregator) based on EasySocial. I basically use it to have multiple authors submits (grab) news from all sorts of places and group them into thems (EasySocial groups in this case)

I create an Author profile type for the content aggregators. I would like registered profile type to be able to comment but not post streams ?

Thanks
Danny