Silver-stained polyacrylamide gel (A) and Western immunblot of LPS reacted with S. marcescens O4-specific antiserum (B). LPS samples were prepared by the method of Darveau and Hancock (3). Lane 1, K. pneumoniae KT776 (wild type); lane 2, K. pneumoniae mutant KT776-1 (wzm-wzt); lane 3, KT776-1 harboring the pST-Blue vector; lane 4, KT776-1 harboring pST6 (wzm-wzt of wbSmO4); lane 5, KT776-1 harboring pST7 (wzm-wzt-wbbA of wbSmO4); lane 6, KT776-1 harboring pSUB6 (complete S. marcescens wbO4 cluster); lane 7, S. marcescens N28b (serotype O4, wild type); lane 8, K. pneumoniae mutant KT776-2 (wbbB); lane 9, KT776-2 harboring the pST-Blue vector; lane 10, KT776-1 harboring pST5 (wbbA of wbSmO4); lane 11, KT776-1 harboring pST7 (wzm-wzt-wbbA of wbSmO4); lane 12, KT776-2 harboring pSUB6 (complete S. marcescens wbO4 cluster).