DNA preparation
For the single clone analysis, colonies were grown in 96 deep well plates. For the mixed clone analysis, 9216 single colonies were inoculated in 24 384- microtiterplates in 50 μl of TYGPN-medium [31] and grown for 48 hours at 37°C. The cultured medium of 96 colonies each was collected by means of a BIOMEK pipetting robot (Beckman) and pooled in one well of a 96 deep well plate. DNA was prepared according to the REAL DNA preparation kit (Qiagen) and dissolved at a concentration of about 100 ng/μl in H2O.