Exo-β-(1→3)-glucan (curdlan) biosynthesis by Agrobacterium sp. ATCC 31749

The present study describes physiological conditions which promote curdlan synthesis, the effect of metabolic inhibitors on production and the nature of the product of Agrobacterium sp. ATCC 31749, a laboratory derivative of a strain originally isolated from soil. Nitrogen depletion in the medium was essential for production, and depletion of sulphur or phosphorus in batch culture did not promote curdlan synthesis. Similarly, initiation of curdlan production was observed when bacteria were transferred to nitrogen free medium but not media free of sulphur or phosphorus. A model of the mechanism of nitrogen dependent control is presented. Agrobacterium sp. ATCC 31749 grew well on a number of monosaccharides and lactose, moderately well on succinate and poorly on glycerol. Good curdlan production was observed from mannose, glucose and galactose with a reasonable curdlan yield obtained from sucrose. Curdlan yields when lactose, maltose or glycerol were supplied were poor and no curdlan was obtained from culture on succinate. The effects of other physiological conditions were examined. Arsenate inhibited neither initiation nor continuation of curdlan biosynthesis when added to the medium in concentrations up to 10mM. 5mM sodium azide inhibited curdlan production but not glucose uptake. A similar effect was observed when the ionophore tetracaine (1mgml^-1) was added to the medium. EDTA inhibited curdlan production and glucose uptake whilst EGTA inhibited neither. Chloramphenicol inhibited curdlan production as did rifampicin. Analysis of the kinetics and degradation products of enzyme hydrolysis revealed a similarity between neutralised gels and gels formed by low temperature heating. Results obtained with native curdlan or curdlan preparations obtained by boiling aqueous suspensions were similar. The implications or these results on curdlan biosynthesis are discussed.