Congo red and calcofluor white inhibition ofAcetobacter xylinum cell growth and of bacterial cellulose microfibril formation: Isolation and properties of a transient, extracellular glucan related to cellulose

Summary

Chemical analysis of pellicles ofAcetobacter xylinum grown in cultures containing increasing amounts of Calcofluor White or Congo Red shows that the inhibition of cellulose formation by both direct dyes has two aspects, internal and external. Internally, each dye seems to act as a general cell poison, although not a strong one. Externally, each dye interrupts cellulose microfibril assembly by forming a complex with previously synthesized polysaccharide(s). Both effects contribute to diminution of cellulose production.

The polysaccharide(s) which forms a soluble complex with Congo Red external to the cell may be isolated by dilution. It is a homoglucan that yields cellobiose, cellotriose and possibly cellotetrose after partial acid hydrolysis. The glucan is hydrolyzed at the same rate as bacterial cellulose by glusulase to yield glucose. It contains little or no ninhydrin-positive material. Observations by electron microscopy show that the glucan is fibrillar. Heating the precipitate in 1 M NaOH for 10 minutes at 100 °C dissolves more than three quarters of the substance but does not alter its ultrastructure or composition. No discrete reflections are observed by powder X-ray diffraction. The foregoing results are consistent with the conclusion that Congo Red (and presumably Calcofluor White) interrupts the normal, extracellular association of previously synthesized 1 → 4-β-glucans by forming a soluble complex with a fraction of these glucans. The interruption of the association prevents the formation of the microfibril.