Structure of Lipopolysaccharide from Is Low Molecular Weight and Offers Insight into Liberibacter Biology.

Huanglongbing (HLB) disease, also known as citrus greening disease, was first reported in the US in 2005. Since then, the disease has decimated the citrus industry in Florida, resulting in billions of dollars in crop losses and the destruction of thousands of acres of citrus groves. The causative agent of citrus greening disease is the phloem limited pathogen Liberibacter asiaticus. As it has not been cultured, very little is known about the structural biology of the organism. are part of the family, which includes nitrogen-fixing symbionts of legumes as well as the plant pathogens. To better understand the genus, a closely related culturable bacterium ( or Lcr) has attracted attention as a model organism for structural and functional genomics of Liberibacters. Given that the structure of lipopolysaccharides (LPS) from Gram-negative bacteria plays a crucial role in mediating host-pathogen interactions, we sought to characterize the LPS from Lcr. We found that the major lipid A component of the LPS consisted of a pentaacylated molecule with a β-6-GlcN disaccharide backbone lacking phosphate. The polysaccharide portion of the LPS was unusual compared to previously described members of the family in that it contained ribofuranosyl residues. The LPS structure presented here allows us to extrapolate known LPS structure/function relationships to members of the genus which cannot yet be cultured. It also offers insights into the biology of the organism and how they manage to effectively attack citrus trees.