Osmotically induced oligo- and polysaccharide synthesis by Rhizobium meliloti SU-47

Abstract

In standard liquid medium containing 5 g mamitoll-' and 1 g glutamic acid 1-l, Rhizobium mefifoti SU-47 cells accumulated 350 mg cyclic 1,2-Q-glucans (g protein)-'. The cyclic glucans were 36 % glycerol-1-phosphatesubstituted and 64% were uncharged. In the same medium with 10 g mamitoll-' , repeating units of succinoglycan (1110 mg 1-l) were found as extracellular carbohydrates, and only low amounts of the succinoglycan polymer (up to 300 mg 1-l) were excreted. By raising the osmotic 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 1-1 at 0.2 M-NaCI 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 l,2-Q-glucans was lowered to 150 mg (g protein)-l out of which the glycerol-1-phosphatesubstituted glucan fraction was reduced to 15%. Instead, high amounts of oligosaccharides were synthesized as osmoprotectants, with trehalose as the major component [up to 200 mg (g protein)-']. Glycogen synthesis was completely suppressed at this salt concentration, while p l y Q-hydroxybutyric acid synthesis was unaffected.

The Molecular Weight Distribution of Succinoglycan Produced by Sinorhizobium meliloti Is Influenced by Specific Tyrosine Phosphorylation and ATPase Activity of the Cytoplasmic Domain of the ExoP Protein

“…When cultured in GMS medium, S. meliloti Rm2011 produced both HMW succinoglycan and LMW succinoglycan, which has been reported to consist of monomers, dimers, and trimers of the octasaccharide subunit (53). Since the mutants with mutations in the ATP-binding motif produced very small amounts of succinoglycan, we increased the osmolarity of the medium to 0.24 M NaCl in order to obtain larger amounts of HMW succinoglycan (10). Fractionation of the supernatants of S. meliloti wild-type and mutant strains on a gel filtration column resulted in three major carbohydrate peaks.…”

“…The production of succinoglycan is influenced by the osmolarity of the growth medium. An increase in osmotic pressure results in enhanced production of HMW succinoglycan at the expense of LMW succinoglycan (10).…”

Characterization of Exopolysaccharides Produced by Rhizobia Species

“…Cold 96 % ethanol was added to the supernatant obtained from centrifugation at a 3:1 (v/v) ethanol:supernatant ratio to precipitate the EPS (Breedveld et al, 1990). The mixture was refrigerated at 4 ºC for 24 h. After the refrigeration period, the samples were centrifuged once more (10,000 g, 4 ºC, 30 min) to separate the precipitate from the solvent.…”

Desiccation-Tolerant Rhizobacteria from Cholistan Desert, Pakistan, and Their Impact on Zea mays L.

“…Exopolysaccharide production has a great interest with respect to desiccation because rhizobacteria undergo adaptations. S. meliloti has shown adaption in the presence of exopolysaccharide under osmotic stress and also affects the survival rate during dry conditions [36,37]. Mary et al [38] observed a decrease in survival rate of rhizobia upon the addition of polysaccharides when dried at an RH of >3%, but survival rate increased to 3% RH.…”