Once a fermentation process is optimized for maximum production, the selected clone is preserved by generating Master and Working Cell Banks following GMP-compliant Master Production Records. The Master Cell Bank (MCB) typically consists of 150-200 vials. Proper characterization of the MCB includes genotypic and phenotypic analyses (purity, identity, viability, plasmid retention and restriction enzyme mapping if extrachromosomal, phage testing if bacterial, gene sequencing, and gene copy number). Once the MCB is released, a Working Cell Bank (WCB) of approximately 200 vials is generated. The WCB undergoes abbreviated testing consisting of purity, identity, viability and restriction enzyme mapping. MCB and WCB seed vials are stored in vapor phase liquid nitrogen (LN2) in continuously monitored LN2 Dewars.