Quantitative PCR for Determination of Copy Number
Immediately prior to induction at OD600 0.2, 1 mL of cell culture was collected and
centrifuged at 16,000g for 1 min. The cell pellet was resuspended in 100 μL of deionized
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water. One microliter of resuspended cell pellet was used directly as the template in a
quantitative PCR (qPCR) reaction with Maxima™ SYBR green/fluorescein qPCR master
mix (Fermentas, Glen Burnie, MD). Primers 24 and 25 were used for BTE amplification,
and primers 26 and 27 for chromosomal ompA amplification. SYBR Green fluorescence
was monitored with a Bio-Rad CFX96 optical reaction module (Bio-Rad, Hercules, CA).
Threshold cycle (Ct
) values were calculated by Bio-Rad CFX Manager software.