The effect of sugars on the morphology of the bacterial flagellum

Using dark-field microscopy, we have found that certain sugars cause the normal-to-curly helical transition of bacterial flagella. Titration of flagella isolated from Salmonella typhimwium with 16 different carbohydrates showed that: (i) only certain sugars cause the transition. There is no obvious relationship between the simple physico-chemical properties of the sugar and whether the sugar causes the transition or not; (ii) the efficacies of sugars that do cause the transition differ markedly. For these sugars there is a relationship between efficacy and molecular size. These results suggest that the specific, though weak, binding of sugars to sites on flagella cause the morphological transition.