INTERACTION BETWEEN FISH SPOILAGE BACTERIA PSEUDOMONAS SP AND SHEWANELLA-PUTREFACIENS IN FISH EXTRACTS AND ON FISH TISSUE

The interaction between fish spoilage bacteria, Pseudomonas sp. and Sh ewanella putrefaciens, was investigated using fish extract and fish ti ssue as model systems. Isolates of Pseudomonas that produced iron chel ators, siderophores, inhibited growth of S. putrefaciens in a fish-ext ract-agar diffusion assay but no, or only weak, antagonistic activity was seen when the medium was supplemented with iran. Sterile-filtered supernatant fluid from a siderophore-producing Pseudomonas grown in fi sh extract was inhibitory to S. putrefaciens if the number of Pseudomo nas was above 10(8) cfu ml(-1). In contrast, supernatant fluids from s iderophore-negative Pseudomonas isolates did not inhibit growth of S. putrefaciens. The inhibitory effect was, except for one strain of Pseu domonas, not seen in supernatant fluids from iron-enriched cultures of Pseudomonas sp. Finally, siderophore-producing Pseudomonas sp. lowere d the maximum cell level of S. putrefaciens 1-2 log units from 10(9) t o 10(10) cfu g(-1) when the strains were grown on fish muscle blocks a t 0 degrees C but the growth rate of S. putrefaciens was not affected.