I am culturing LentiX HEK293 cells and noticed round particles in cell culture. They are about 1-3 microns in diameter, so unlikely to be mycoplasma (which are
1. Those are apoptotic bodies which contains DNA too.
Read:
At later stages of apoptosis, cells can disassemble and generate subcellular (generally 1–5 μm in diameter) membrane-bound extracellular vesicles termed apoptotic bodies Like exosomes and microvesicles, ApoBDs are classified as a type of extracellular vesicle (EV), which can be generated from many (but not all) cell types, including T cells, monocytes, fibroblasts, endothelial cells and epithelial cells. It has also been shown that they can carry DNA, microRNAs, proteins and lipids to mediate communication between cells.
2. bacteria that can't grow well in the medium with antibiotics.
I agree that, most likely, these round particles are apoptotic bodies.
I have worked with Phoenix_Ampho cells (which are also a HEK293 cell line) and I have noticed these bodies when the cells were not so happy. Therefore, I highly recommend to chech the splitting & /or culturing conditions of your LentiX HEK293.
Finally, I have attached a picture my Phoenix_Ampho cells taken when they were happy.