Lipopolysaccharide (LPS) is the major surface molecule of Gram-negative bacteria consisting of O-antigen polysaccharides, the core and the hydrophobic lipid A anchored in the outer membrane. Ca. Liberibacter spp. are uncultured, phloem-limited bacterial plant pathogens associated with plant diseases such as citrus greening (Huanglongbing) and potato zebra chip. L. crescens (Lcr) is a nonpathogenic, but cultured surrogate for functional genomic studies of pathogenic Ca. Liberibacters. The lipid A from Lcr has a traditional penta-acylated chitobiose backbone with two ester-linked C16:0 (3-OH) and two amide-linked C14:0 (3-OH) fatty acid residues. Lcr lipid A also contains a very long chain fatty acid (VLCFA) C28:0 (26-OH), a unique feature of bacteria such as Sinorhizobium meliloti and Brucella abortus that form chronic intracellular infections within eukaryotic hosts. Absence of VLCFA-LPS in S. meliloti increases sensitivity to salt, detergents and pH etc. S. meliloti genes lpxXL (SMc04268) and acpXL (SMc04278) encode a lipid A C28 acyltransferase and an acyl carrier protein involved in the biosynthesis of VLCFA-modi?ed lipid A. Homologs for both these genes are present in Lcr (B488_RS04675 and B488_RS04700, respectively) but absent in all pathogenic Liberibacters. Knockout mutations of several Lcr genes were readily obtained, but not mutations of lpxXL or acpXL, suggesting that VLCFA-modified lipid A may be essential for axenic growth of pathogenic Liberibacters.