Martin S. Springer

Failure of sensory adaptation in bacterial mutants that are defective in a protein methylation reaction

Chemotactic bacteria, such as E. coli, detect changes in the chemical composition of the environment. Addition of an attractant or repellent leads to an immediate response, characterized by a change in the swimming behavior of the cells--a process known as sensory excitation. However, the response gradually disappears with time, despite the continued presence of the chemical--a process known as sensory adaptation. We report here the behavior of a class of nonchemotactic mutants (cheX) that can carry out sensory excitation but are defective in the process of sensory adaptation. These mutants are also defective in the ability to carry out a protein methylation reaction which has previously been implicated in the adaptation process (Goy, Springer and Adler, 1977). The results presented here establish a firm relationship between the methylation reaction and sensory adaptation.

Pleiotropic aspartate taxis and serine taxis mutants of Escherichia coli.

Mutants that at one time were thought to be specifically defective in taxis toward aspartate and related amino acids (tar mutants) or specifically defective in taxis toward serine and related amino acids (tar mutants) are now shown to be pleiotropic in their defects. The tar mutants also lack taxis toward maltose and away from Co2+ and Ni2+. The tsr mutants are altered in their response to a variety of repellents. Double mutants (tar tsr) fail in nearly all chemotactic responses. The tar and tsr mutants provide evidence for two complementary, converging pathways of information flow: certain chemoreceptors feed information into the tar pathway and others into the tsr pathway. The tar and tsr products have been shown to be two different sets of methylated proteins.