RPA1 and infection: For example, insertional inactivation of btuB, that encodes a vitamin B12 (cobalamin) transporter, was identified as a susceptibility gene for infection by phage SPLA5b (Fig. 3D), while genes such as those in the rfa and rfb loci involved in the biosynthesis of LPS were identified for SPLA1a, SPLA1b, and SPLA5c (Fig. 3A, B, and E).