Abstract: Three Gram-negative bacteria were isolated from the commercial fresh fish and considered to be the pseudomonas group , an important microorganism that caused the fish spoilage ,by analysis of 16SrDNA sequence.The characteristics (Protase ,siderophore(s) ,formation biofilm) involved food spoilage were assayed . N-acyl-homoserine lactones (AHLs) were the important quorum sensing molecules and regulated the expression of many characteristics in Gram-negative .Three isolates produced the AHLs incolved in quorum sensing.Thin-layer chromatography revealed presence of two AHLs in extract from the Pseudomonas fluorescens FLM05-1and Pseudomonas fluorescens FLM05-2 and the main signal molecule was N-3-oxo-octanoyl-homoserine lactone.Production siderophore , protase of FLM05-2 were significantly reduced by co-incubation with AHL degrader Pseudomonas fluorescens P3(pME6863). It was suggested that QS play an important role in the food spoilage. This was first study of production AHLs ,quorum sensing signal molecule by the pseudomonas , and new strategies were provided for food preservation based on quorum sensing

Key words: Pseudomonas, Biofilm, siderophore(s), Protase, N-acyl- homoserine lactones, Quorum sensing, Food spoilage