Germination arrest factor (GAF): Part 2. Physical and chemical properties of a novel, naturally occurring herbicide produced by Pseudomonas fluorescens strain WH6

Pseudomonas fluorescens isolate WH6 and several related isolates have been shown previously to produce and secrete a novel, naturally occurring herbicide that arrests germination of the seeds of a large number of grassy weed species. The physical and chemical characteristics of this Germination Arrest Factor (GAF) have been investigated in the present study. GAF was insoluble in all organic solvents tested with the exception of methanol, in which it was moderately soluble. However, appropriate concentrations of aqueous ethanol solutions could be used to extract GAF from dried WH6 culture filtrates. GAF activity was destroyed by heating at temperatures in excess of 65 °C, but no obvious loss of activity was observed after exposure for several hours at room temperature to either acid or alkaline conditions within the pH range 2–12. GAF activity in the culture filtrate gradually declined during prolonged storage at 4 °C. Ultrafiltration and gel filtration studies indicated that GAF activity was associated with a compound or compounds having a molecular weight less than 1000. As expected from its solubility properties, GAF activity did not bind to reverse-phase materials (e.g., silica-C18 cartridges). The very hydrophilic character of the GAF molecule suggests that it does not contain an aromatic ring structure. GAF was retained on an anion exchange column, indicating that the active molecule must contain an acid group.