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In standard liquid medium containing 5g mannitol l−1and 1g glutamic acid l−1, Rahizobium meliloti SU-47 cells accumulated 350 mg cyclic 1,2-β-glucans (g protein)−1. The cyclic glucans were 36% glycerol-1-phosphatesubstituted and 64% were uncharged. In the same medium with 10 g mannitol l−1, repeating units of succinoglycan (1110 mg l−1) were found as extracellular carbohydrates, and only low amouns of the succinoglycan polymer (up to 300 mg l−1) were excreted. By raising the omotic pressure of the medium by the addition of NaCl or other ionic and non-ionic osmolytes, succinoglycan production could be stimulated: up to 2·4 g l−1at 0·2 m-NaCl was produced at the expense of the repeating units. Above 0·2 m-NaCl growth was slowed down, and succinoglycan excretion diminished. At 1 m-NaCl growth stopped completely. In standard medium containing 0·6 m-NaCl the amount of cellular cyclic 1,2-β-glucans was lowered to 150 mg (g protein)−1out of which the glycerol-1-phosphatesubstituted glucan fraction was reduced to 15%. Instead, high amounts of oliogosaccharides were synthesized as osmoprotectants, with trehalose as the major component [up to 200 mg (g protein)−1]. Glycogen synthesis was completely suppressed at this salt conenctration, while poly β-hydroxyutyric acid syntheis was unaffected.
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