Screening for microorganisms associated with M74 disease syndrome in sea-run Baltic salmon (Salmo salar)

The aim of this project was to determine whether there is an association be tween a pathogenic microorganism associated with a maternal pathologic lesi on, or a maternal metabolic impairment arising from disturbed homeostasis c aused by changes in the symbiotic microflora, and the M74 fry mortality syn drome in Baltic salmon. A broad screening approach was taken, using convent ional methods for isolating and identifying fungi, bacteria, and viruses. B acteria were identified using specific sequences of 16S rRNA, and microbe i dentification based on the analysis of differences between 2 complex genome s using a DNA subtractive methodology; representation difference analysis ( RDA). The selection of tissue sites to be isolated was based on histopathol ogical findings. Bartonella spp., which are known to be associated with inf lammatory cardiac diseases in other animals, were not found to be associate d with coronary arterial lesions in sea-run Baltic salmon. During the long starvation period during spawning migration, essential substances such as v itamins may be provided by the salmon's symbiotic intestinal micro flora. F rom the gastrointestinal (GI) tract of adult sea-run Baltic salmon, we were able to isolate Aeromonas sobria, Pseudomonas putrefaciens, Pseudomonas sp p., A. hydrophila and Hafnia alvei, all of which can produce vitamin B-2. P . putrefaciens and Pseudomonas spp. isolated from the GI tract also produce small amounts of Vitamin B,. Furthermore, it was found that chemotheraputi c treatment of spawning salmon with formalin seems to disturb the symbiotic GI-flora. Upon completion of the present investigations we should be able to conclude whether or not M74 is due to anthropogenic disturbances, caused by chemotherapeutic agents or other anthropogenic pollutants in the enviro nment, which compromise maternal health and lead to the activation of a pat hogen or the disruption of vitamin production by symbionts.