THE COLONIAL GREEN ALGA ASTREPHOMENE GUBERNACULIFERA DISPLAYS A CHEMORESPONSE TO ACETATE

Astrephomene gubernaculifera is a colonial green alga capable of growth on sodium acetate in the dark. Because heterotrophic organisms often have mechanisms to detect and respond to food sources, we tested the response of A. gubernaculifera to a number of potential chemoeffectors. Acetate elicits strong chemoaccumulation in three different behavioral assays. However, there was no chemoaccumulation in response to the carbohydrates xylose, ribose, glucose, galactose, mannose, arabinose, fructose, maltose, lactose, and sucrose; the amino acids asparagine, arginine, cysteine, glutamine, glycine, histidine, isoleucine, lysine, phenylalanine, serine, threonine, and hydroxyproline; or glycerol. Interestingly, A. gubernaculifera did respond to propionate. This compound is structurally related to acetate, but is incapable of supporting growth in the dark. This implies that the chemosensory response in A. gubernaculifera is not the direct result of metabolic changes but rather involves a specific chemical receptor and subsequent internal signaling pathway. We are presently analyzing swimming patterns in colonies exposed to changes in acetate concentration to test several alternate models that could lead to chemoaccumulation.