Multiple ori sequences pertaining to different hosts are usually present in a plasmid. But how many different ones can I have, without causing problems?
If problems do get created, what kind of problems are they?
As long as you have one functional ori in E.coli then you theoretically can have as many other oris as you want since they are not active in E.coli (some exception do apply where you can have two active e.coli oris, for example BACs that have inducible copy number). In practice the problem when you have two active oris is plasmid instability, 2nd the sequence of other oris, for example yeast specific one could contain repeats and/or have AT rich sequence that can also destabilize the plasmid.
It depends on what organism these oris are active in. If they're optimized for different species, then theoretically you can add as many as you want (I like to add one high-copy number ori for E. coli DH5alpha for plasmid production and one a little "tamer" ori for the destination organism). However if you want to use different origins that work in E. coli, then you have to look up if they might interfere with each other.
If the origins are exceptionally large however, they could destabilize the plasmid by adding too many AT-rich sequences or repetitive or complementary regions, so I would go for smaller oris, if you want to add more than two.
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