AUTHOR=Liu Yilei , Bellich Barbara , Hug Sebastian , Eberl Leo , Cescutti Paola , Pessi Gabriella 

TITLE=The Exopolysaccharide Cepacian Plays a Role in the Establishment of the Paraburkholderia phymatum – Phaseolus vulgaris Symbiosis

JOURNAL=Frontiers in Microbiology

VOLUME=Volume 11 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01600

DOI=10.3389/fmicb.2020.01600

ISSN=1664-302X

ABSTRACT=Paraburkholderia phymatum is a rhizobial strain that belongs to the beta-proteobacteria, a group known to form efficient nitrogen-fixing symbioses within root nodules of several legumes, including the agriculturally important common bean. The establishment of the symbiosis requires the exchange of rhizobial and plant signals such as lipochitooligosaccharides (Nod factors), polysaccharides and flavonoids. Inspection of the genome of the competitive rhizobium P. phymatum revealed the presence of several polysaccharide biosynthetic gene clusters. In this study, we demonstrate that a cluster of 22 genes (bce) involved in the production of the polysaccharide cepacian, an important component of biofilms produced by closely related opportunistic pathogens of the Burkholderia cepacia complex (Bcc), is required for efficient plant colonization. Wild-type P. phymatum was shown to produce cepacian while a bceN (GDP-D-mannose 4,6-dehydrase) mutant did not. Additionally, the bceN mutant produced a significantly lower amount of biofilm and formed less root nodules compared to the wild-type strain with Phaseolus vulgaris as host plant. Finally, expression of the cepacian cluster was induced by the presence of germinated P. vulgaris seeds under nitrogen limiting conditions suggesting a role of this polysaccharide in root attachment, the first step in the establishment of this ecologically important symbiosis.