Biotin bioassay-based cross-feeding experiments were performed to elucidate the effect on biotin production by bioRbme expression in Agrobacterium tumefaciens (A. tumefaciens) (Feng et al., 2013). The indicator strain used here is the biotin auxotrophic strain of Escherichia coli (E. coli), ER90 (ΔbioF bioC bioD), which was cross-fed by A. tumefaciens species (Feng et al., 2013a). The biotin-free M9 minimal medium plates were formulated as described by other and our research groups (Feng et al., 2013b; Lin et al., 2010; del et al., 1979). Of note, 0.01% (w/v) the redox indicator 2, 3, 5-triphenyl tetrazolium chloride (TTC) was supplemented into the above media. Consequently, biotin generation/production was observed via the reduction of TTC to the insoluble red formazan which is due to the ER90 growth fed by A. tumefaciens strains (Feng et al., 2014). Detailed procedures are described as follows.
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