Negative chemotaxis inSpirochaeta aurantia

Abstract

A repellent-gradient tube assay for negative chemotaxis inSpirochaeta aurantia was developed and used to demonstrate that acids, alcohols, and sulfide were effective chemorepellents. The threshold concentrations (the lowest concentration of a repellent that elicited a detectable response) for benzoic acid, salicylic acid, and butyric acid were 3×10⁻⁵ M. For acetic acid, propionic acid,p-aminobenzoic acid, propanol, butanol, and sulfide, threshold concentrations were 10⁻³ to 10⁻⁴ M. For formic acid, glyoxylic acid, glycolic acid, lactic acid, malonic acid, succinic acid, fumaric acid, methanol, ethanol, ethanediol, and propanediol, threshold concentrations were 10⁻² to 10⁻³ M. Compounds such as methylamine, ethanolamine, formaldehyde, benzene, toluene, phenol, indol, nickel, and various amino acids did not elicit a repellent response. The results of competition experiments suggest that the repellents identified are recognized by three distinct receptors: a weak acid receptor, an alcohol receptor, and a sulfide receptor. The repellent responses to weak acids were maximal at pH 5.5 and decreased with increasing pH, whereas the response to propanol was unaffected by pH over a range of 5.5–8.0. The demonstration of negative chemotaxis inS. aurantia and the identification of distinct classes of repellents will allow further experimentation directed at understanding chemosensory mechanisms in spirochetes.