SMALLEST CELL: Mycoplasma. The pink circles are a type of bacterium only 0.1 μm in diameter (0.0001 mm, or about 0.0000039 inches).
• They have the fewest known genes of any free living organism. Mycobacterium laboratorium is synthetic bacterium patented by Craig Venter, who has whittled down the minimum number of genes to 382.
• Lacking a cell wall, they are immune to common antibiotics like penicillin that target cell wall synthesis. M. pneumoniae and M. genitalium cause human disease.
• In the lab, they are a common contaminant of cell culture and can seriously confound results. Difficult to detect unless one specifically looks for them, mycoplasma contamination is estimated at minimum of 10%.
Scanning Electron Micrograph: Kevin MacKenzie, University of Aberdeen, Wellcome Images. Mycoplasma on surface of bone-forming osteoblast cells.