multiple organisms in the context of over-expressed protein for pull down

Hi, I am annotating a dataset where the authors express mouse proteins in human cells for pull down. I am not sure how to handle the field "characteristics[organism]".
Also, is there a way to add the tag of the bait?
Thank you for your help.

No files or tests are named in the issue. Start by reviewing the SDRF guidance and existing examples for characteristics[organism] and bait annotations; document the expected handling of mixed organisms and whether a bait tag is supported, then add or update the relevant guidance once the project maintainers confirm the intended convention.

Written by the indexing model from the issue text.