MYXOSPORE INDUCTION IN STIGMATELLA AURANTIACA

Abstract

The existence of different types of induction-resistant mutants allows one to classify all known inducers into one of 3 groups; 1) the glycerol group, 2) the phenethyl alcohol group, and 3) the t-butanol group. This pattern, and the occurrence of specific antagonists which competitively inhibit inducers of the glycerol group (e.g. oxindole, pyrrole), suqgest that the inducers work by interaction with group-specific receptors on the bacterial cell: receptor I for the glycerol aroup, receptor II for the phenethyl alcohol group, receptor III for the t-butanol group of inducers. There are only few inducers which may act on more than one receptor; as isopropanol (receptors I+III), or indole (receptors I+II). In order to become effective as an inducer, a compound needs an attachment site which is responsible for its affinity to the receptor, and a reaction site which determines the intrinsic activity of the inducer. The reaction site of inducers of the phenethyl alcohol group may be the aromatic ring, that of the glycerol group a positive charge or dipole moment, for those are the only functional groups common to all members of the respective groups. The conversion of t-butanol, which is a competitive inhibitor of glycerol induction, into t-butylamine, which induces at the glycerol receptor, seems to demonstrate that the amino group is the reaction site of the molecule. Indeed, introduction of different group-specific reaction sites into a certain molecule changes the receptor specificity of the latter: t-butanol - receptors (I+) III; phenylpropanol - receptor II;t-butylamine - receptors I. The dose-response curves of myxospore induction are sigmoidal. This indicates that induction is an all-or-nothing reaction. Inducers of different groups if applied at concentrations which lie below the lowest inducing concentration of each of them, add their individual effects. This suggests that 1) the stimulus for myxospore induction is the same with all types of inducers, and that 2) the stimulus has to reach a threshold value before sporulation can occur. It was possible to calculate the interaction of 2 different inducers, or of an inducer and an inhibitor. The exact agreement between predicted and experimentally determined effect indicates that our hypothesis and of inducer-receptor-stimulus may come close to reality.