Sorbitol promotes growth of Zymomonas mobilis in environments with high concentrations of sugar: evidence for a physiological function of glucose-fructose oxidoreductase in osmoprotection.
The gram-negative ethanologenic bacterium Zymomonas mobilis is able to grow in media containing high concentrations of glucose or other sugars. A novel compatible solute for bacteria, sorbitol, which enhances growth of Z. mobilis at glucose concentrations exceeding 0.83 M (15%), is described. Added sorbitol was accumulated intracellularly up to 1 M to counteract high external glucose concentrations (up to 1.66 M or 30%). Accumulation of sorbitol was triggered by a glucose upshift (e.g., from 0.33 to 1.27 M or 6 to 23%) and was prevented by the uncoupler CCCP (carbonyl cyanide m-chlorophenylhydrazone; 100 microM). The sorbitol transport system followed Michaelis-Menten kinetics, with an apparent Km of 34 mM and a Vmax of 11.2 nmol.min-1.mg-1 (dry mass). Sorbitol was produced by the cells themselves and was accumulated when growing on sucrose (1 M or 36%) by the action of the periplasmic enzyme glucose-fructose oxidoreductase, which converts glucose and fructose to gluconolactone and sorbitol. Thus, Z. mobilis can form and accumulate the compatible solute sorbitol from a natural carbon source, sucrose, in order to overcome osmotic stress in high-sugar media. No other major compatible solute (betaine, proline, glutamate, or trehalose) was detected.
Loos
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H
Institut für Biotechnologie 1, Forschungszentrum Jülich GmbH, Germany.
Krämer
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R
Sahm
H
H
Sprenger
G A
GA
D000222:Adaptation, Physiological; D001692:Biological Transport; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D008954:Models, Biological; D009997:Osmotic Pressure; D010088:Oxidoreductases / Q000378:metabolism*; D013012:Sorbitol / Q000378:metabolism* / Q000494:pharmacology; D013395:Sucrose / Q000378:metabolism; D017355:Zymomonas / Q000254:growth & development*
D005632:Fructose; D013012:Sorbitol; D013395:Sucrose; D010088:Oxidoreductases; C074291:glucose-fructose oxidoreductase; D005947:Glucose