Nitrous oxide producing heterotrophic bacteria from the water column of the central Baltic: abundance and molecular identification

The water column of the Gotland Deep, a basin with anoxic deep water in the central Baltic, was investigated for its denitrifying microflora in comparison with various chemical, hydrographical and microbiological parameters including in situ denitrlfication rates. Abundance of denitrifying bacterla was determined by the MPN method using nutrient broth plus nitrate medium. As gas formation in inverted vials turned out to be a rather variable feature, N 2 0 production was used to detect the presence of denitnfying bacteria. Using 4 different cultivation approaches, 77 N 2 0 producing strains were Isolated from the whole water column. Isolates were analyzed for their denitrifying capacity to form NO2-, N20 , and NZ. Taxonomic identification of the strains was done by high resolution electrophoresis of their low-molecular-weight (LMW) RNA (5s rRNA and tRNA). The bulk of the isolated N 2 0 producing strains (77 %) was identified by their LMW RNA pattern as Shewanella putrefaciens. All strains of this species produced N20 , and NO2and about one third showed N2-formation. S. putrefaciens is considered the most abundant culturable denitrifier of the low oxygen water and the oxicanoxic interface of the Gotland Deep.