They seem to me dead cells but your information is really imperfect.

If you want to be sure, just culture it on microbiological medium.

Regards.

These large oval shape cells can be some sort of fungal contamination. Normally, they very difficult to get rid of.

Thank you.

Thank you both Alireza and Amal. They don't look to have specific particles inside the round line.. it looks like lipid structures at the bottom of the flask. I will check as you suggest. Thank you!

Dear Stella,

Check whether they are yeast cells.

Thank you.

Dear Stella

Check the plates before using, or try to wipe the outer parts with ethanol, it can be residues from the manufacturing