There are various studies on the toxicological potentials of conventionally synthesized zinc oxide (ZnO) nanoparticles, which are useful tools for many industrial applications. However, knowledge about the biologically synthesized ones is still limited. The current study was designed to biologically synthesize ZnO nanoparticles from zinc acetate, zinc chloride, zinc nitrate hexahydrate and zinc sulfate heptahydrate precursors by Rhodococcus erythropolis K85 and assess their toxicological potentials on Triticum aestivum. ZnO nanoparticles were successfully synthesized from each precursor and characterized by scanning electron microscopy (SEM) observations and energy-dispersive X-ray spectroscopy (EDAX) analysis. The size of produced nanoparticles ranged from 50 to 150 nm and none of the test groups affected seed germination at 0.1 mg/ml concentration. However, seedling growth was significantly affected by ZnO nanoparticle exposure. Besides, random amplified polymorphic DNA (RAPD) analysis results showed a conformity to the seedling growth results and all of the test groups caused significant changes in the RAPD profiles for OPA-2, OPA-13, OPH-19, OPW-6, OPW-11, OPW-17, OPW-18 and OPY-8 primers. This resulted in a significant decrease in genomic template stability percentage (GTS%) and an increase in polymorphism percentage values. In conclusion, this study confirms that ZnO nanoparticles may show significant toxicological features – even if they are biologically synthesized and it is necessary to determine their hazardous potential before use.