Plant host and sugar alcohol induced exopolysaccharide biosynthesis in the Burkholderia cepacia complex.
The species that presently constitute the Burkholderia cepacia complex (Bcc) have multiple roles; they include soil and water saprophytes, bioremediators, and plant, animal and human pathogens. Since the first description of pathogenicity in the Bcc was based on sour skin rot of onion bulbs, this study returned to this plant host to investigate the onion-associated phenotype of the Bcc. Many Bcc isolates, which were previously considered to be non-mucoid, produced copious amounts of exopolysaccharide (EPS) when onion tissue was provided as the sole nutrient. EPS production was not species-specific, was observed in isolates from both clinical and environmental sources, and did not correlate with the ability to cause maceration of onion tissue. Chemical analysis suggested that the onion components responsible for EPS induction were primarily the carbohydrates sucrose, fructose and fructans. Additional sugars were investigated, and all alcohol sugars tested were able to induce EPS production, in particular mannitol and glucitol. To investigate the molecular basis for EPS biosynthesis, we focused on the highly conserved bce gene cluster thought to be involved in cepacian biosynthesis. We demonstrated induction of the bce gene cluster by mannitol, and found a clear correlation between the inability of representatives of the Burkholderia cenocepacia ET12 lineage to produce EPS and the presence of an 11 bp deletion within the bceB gene, which encodes a glycosyltransferase. Insertional inactivation of bceB in Burkholderia ambifaria AMMD results in loss of EPS production on sugar alcohol media. These novel and surprising insights into EPS biosynthesis highlight the metabolic potential of the Bcc and show that a potential virulence factor may not be detected by routine laboratory culture. Our results also highlight a potential hazard in the use of inhaled mannitol as an osmolyte to improve mucociliary clearance in individuals with cystic fibrosis.
Bartholdson
S Josefin
SJ
Centre for Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK.|School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK.
Brown
Alan R
AR
Centre for Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK.
Mewburn
Ben R
BR
Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH9 3JH, UK.
Clarke
David J
DJ
School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK.
Fry
Stephen C
SC
Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH9 3JH, UK.
Campopiano
Dominic J
DJ
School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK.
Govan
John R W
JRW
Centre for Infectious Diseases, University of Edinburgh, Edinburgh EH16 4SB, UK.
D042602:Burkholderia cepacia complex / Q000235:genetics / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D019697:Onions / Q000737:chemistry / Q000378:metabolism*; D010936:Plant Extracts / Q000737:chemistry / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis* / Q000235:genetics; D013402:Sugar Alcohols / Q000378:metabolism*
D010936:Plant Extracts; D011135:Polysaccharides, Bacterial; D013402:Sugar Alcohols