Cyclosophoran

Cyclosophorans Agrobacterium sp., Rhizobium sp., Xanthomonas sp. Cyclic (1 — 2)- 8-D-glucans... 

Preparation of cyclosophorans is restricted because the bacteria secrete a highly viscous extracellular polysaccharide (EPS). This extracellular slime restricts aeration of the broth, hinders removal of bacterial cells, and hence the separation of the glucan. Transposon mutagenesis has been used to produce E S-Rhizobium leguminosarum which produce cyclosophorans but no longer produce EPS. The bacterial broths can... 

Figure 4. Distribution of molecular sizes (degree of polymerization - dp) for cyclosophorans produced by an Z S-Rhizobium leguminosarum species. Separation on Zorbax ODS, 3000 nm, 9.4 x 250 mm column (a) Eluant 3% CHaOH, 1.5 mL/min increased to 2.5 mL/min, 10 mg loading, (b) Eluant 2% CHaOH, 2.5 - 2.7 mL/min, 0-8 mg loading.

Present studies at IFR are concerned with the development of methods for examining potential complex formation with purified cyclosophorans. Preliminary studies have been carried out on the macrolide antibiotic Amphotericin B (AmB). This material is a potent systemic fungicide but its considerable toxicity and poor solubility have restricted its therapeutic applications. Attempts to improve water solubility, and thus lessen the aggregation of AmB, by derivatization have resulted in decreasing activity. Recently it has been reported that AmB can be solubilized by complexation with 7"cyclodextran and that the complex retains the full anti-fungal activity. 4 ... 

Figure 5. Circular dichroism spectrum for a micellar suspension of AmB in water. Data collected on a JASCO J-600. Curve 1 shows the original spectrum and curve 2 the effect of adding cyclosophorans to the AmB dispersion.

The cyclosophorans are secreted into the culture medium but are also found associated with the cell [31]. Cellular concentrations range between 5 and 20% of the total dry cell weight. They are located primarily in the periplasmic space. Their secretion from the cell varies greatly for the different species and is influenced by the stage of growth and conditions of growth such as the composition of the medium and the temperature [39,40]. Large amounts of extracellular cyclosophorans are found after the stationary phase of the culture has been reached [39-41]. 

The cyclosophorans are sometimes substituted with anionic substituents such as 1-phosphoglycerol, succinic acid, and methyl malonic acid [42-46] 1-phos-... 

D-glucan apparently has similar roles for the bacteria, as do the cyclosophorans. 

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