Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2009
Publication Date: 8/31/2009
Citation: Banowetz, G.M., Azevedo, M.D., Armstrong, D., Mills, D. 2009. Germination Arrest Factor (GAF): 2. Physical and chemical properties of a novel, naturally-occurring herbicide produced by Pseudomonas fluorescens strain WH6.. Biological Control. 50:103-110.
Interpretive Summary: The physical and chemical characteristics of a new product with herbicidal properties isolated from a soil bacterium were determined. These characteristics were needed to develop an approach to purify the molecule responsible for the herbicidal activity so that the structure and be determined. Determination of the structure will be important in the eventual commercialization of this bioherbicide that appears to be very effective in arresting the germination of grassy weed seeds.
Technical Abstract: 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 activity 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 activity from dried WH6 culture filtrates. GAF activity was destroyed by heating at temperatures in excess of 65 oC, 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 to 12. No change in GAF activity was observed after exposure of WH6 culture filtrates to several types of hydrolytic enzymes. GAF activity in the culture filtrate gradually declined during prolonged storage at 4 oC. 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), but it was retained on an anion exchange column, indicating that the active molecules must contain an acid group.