Figure 1.

Isolation of the evolved PB12 strain. The isolation of PB12 has previously been reported and is included to provide orientation to the reader and for discussion purposes [10]. The evolutionary process that generated the PB12 strain initiated with the parental PB11 strain that lacks the PTS system. Deletion of this system generates a carbon stress response when PB11 is grown in glucose as the sole carbon source [9,13]. This strain that grows very slowly in glucose and generates white colonies (WC) in glucose-McConkey agar plates, was grown in a batch culture fermentor containing minimal medium with 2 g/l of glucose as the sole carbon source and 30 μg/ml of kanamycin. Under these conditions, a selection pressure is generated, favoring faster growing mutants. The culture was maintained until the stationary phase and then a continuous culture was initiated by feeding a glucose solution at progressively higher dilution rates in the same medium. Dotted line indicates the end of the batch culture and the start of the continuous culture. This procedure allowed the isolation of mutants according to their growth rates. Samples were monitored on glucose-McConkey agar plates to identify red colonies as an indicative of glucose utilization [Glc+ phenotype. Red colonies (RC) were detected after a period of 70 hr. The arrows indicate the isolation time for several Glc+ variants including PB12. Numbers indicate different dilution rates (D = h-1). All the isolated colonies from this culture carry the same large deletion present in strain PB12 (data not shown). This figure was derived and modified from figure 1 from Flores et al. 2007 [10]

Aguilar et al. BMC Genomics 2012 13:385   doi:10.1186/1471-2164-13-385
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