An unusual galactofuranose lipopolysaccharide that ensures the intracellular survival of toxin-producing bacteria in their fungal host.

Burkholderia rhizoxinica is an intracellular symbiont of the filamentous fungus Rhizopus microsporus. Producing the antimitotic macrolide rhizoxin, it serves its host as ‘intracellular toxin factory’. While macrolide biosynthesis by bacterial endosymbionts has been studied intensively, little is known about how endobacteria can survive within fungal host cells and how they interact with their host by ways of chemical recognition and communication. Given the above premises we wanted to understand if the LPS from Burkholderia rhizoxinica is one of the molecular determinants in the interaction of the organism with the fungus. Therefore, in this work we have determined the structure of the LPS from B. rhizoxinica wild-type (wt) and its O-antigen ligase mutant. In addition, we present a gene cluster involved in LPS biosynthesis and deliver first evidence that LPS plays a role in the symbiosis.