Identification of chromosomal genes located downstream of dctD that affect the requirement for calcium and the lipopolysaccharide layer of Rhizobium leguminosarum

A Tn5 mutant (RU301) of R. leguminosarum that lacks the O-antigen, and which has rough colony morphology and is unable to swarm in TY agar, produces only lipopolysaccharide layer (LPS II). RU301 fails to grow on organic acids but high concentration of calcium or magnesium restores the growth. Southern blotting shows the location at transposon insertion in RU301 in a 3 kb EcoRI fragment. There is a separation of 10 kb between dctD and the region mutated in strain RU301. Additional calcium is not necessary for all LPS rough mutants, and gene mutation in RU301 is essential for nitrogen fixation.