Magnetotactic bacteria synthesize pure morphologically precise nano-magnetite crystals called magnetosomes. Doping magnetosomes varies their magnetic properties, making them very promising nanomaterials. Here we present the highest doping of Co²⁺ (3.0%), Mn²⁺ (2.7%) and Cu²⁺ (15.6%) into magnetosomes in vivo. Most significantly, the first report of Cu-doping in magnetite magnetosomes and the highest metal doped into magnetosomes recorded. A 2-fold increase is recorded for Mn and Co doping over previous reports.