BIOTIN CHEMORESPONSE IN PARAMECIUM

Paramecium tetraurelia locate their foodsource by detecting bacterial metabolites and altering swimming behavior to congregate near bacteria l populations on which they feed. Several attractants, such as folate, glutamate, cAMP and acetate have been identified and various aspects of chemoreception, signal transduction and effector mechanisms have be en described. Here we characterize the Paramecium chemoresponse to bio tin. An essential enzymatic cofactor in all cells, biotin is secreted by a large number of bacterial species during growth phase. P. tetraur elia are strongly attracted to biotin with a half-maximal behavioral r esponse at 0.3 mmol.l(-1) in T-maze assays. Physiological recordings f rom whole cells show that cells hyperpolarize in a concentration-depen dent manner in biotin. Whole-cell binding assays utilizing H-3-biotin identify a saturable and specific binding site with an apparent dissoc iation constant of 0.4 mmol.l(-1). The biotin analogs desthiobiotin an d biotin methyl ester are also strong attractants. Diaminobiotin fails to attract P. tetraurelia at 1 mmol.l(-1), but does interfere with th e biotin chemoresponse and displaces H-3-biotin from whole cells. We h ypothesize that the keto group and/or fidelity of the ureido ring of b iotin are necessary for biotin chemoresponse.