Abstract
Previously, we constructed a lactose-utilizing strain of Xanthomonas campestris, Xc17 (pKMϕLT), by cloning lacZY genes with the RK2-derived vector pLAFR1. In this study, the narrow-host-range, β-galactosidase expression plasmid pKMϕ was fused with an integration vector pS19 to form pSFϕ14. Following insertion into Xc17, pSFϕ14 was integrated into the host chromosome. The integration function was provided by the 0.85-kb EcoRI-PstI fragment from the filamentous phage ϕLf. The integration caused no adverse effect to the cells and was stable for at least 66 generations without selection. The engineered strain, Xc17::pSFϕ14, was able to grow as well and produce as much xanthan gum in lactose medium as the wild-type cells did in glucose medium, and the Xc17(pKMϕLT) in lactose medium. Therefore, Xc17::pSϕF14 is potentially useful for xanthan production by direct use of whey lactose as the fermentation substrate. This study has advanced one more step our efforts to contruct lactose-utilizing X. campestris and confirmed the feasibility of using pS19 as an integration vector.
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