Phylogeny and abundance of novel denitrifying bacteria isolated from the water column of the central Baltic Sea

The Baltic Sea is an estuarine ecosystem where denitrification in the low o xic and anoxic parts of the deep water contributes significantly to the nit rogen budget. Seventy-six heterotrophic, denitrifying, strains have been is olated by four cultivation procedures from the water column of the Gotland Deep, the main anoxic basin of the Central Baltic. Phylogenetic positions o f representative strains of 10 different genotypes, grouped beforehand by l ow molecular weight (LMW) RNA profiling, were estimated by 16S rRNA sequenc e analysis. The 10 genotypes consisted of two members of the alpha subclass of the Proteobacteria and eight members of the gamma subclass. The major f raction of the genotypes was considered to be novel species or even genera. The gamma-Proteobacteria were the most abundant of the denitrifying isolat es (96% of the total isolates) with a predominance of Shewaneila baltica (7 7%), whereas the alpha-Proteobacteria were represented by single isolates. The diversity spectrum of Baltic sea denitrifying isolates was rather disti nct from that previously described for marine and freshwater environments. Denitrifying bacteria could be isolated from all depths of the water column with the highest diversity and abundance of genotypes detected in samples of the oxic-anoxic interface, the layer of high in situ denitrification. Fo r success of isolation of phylogenetically divers denitrifiers, both sample origin and cultivation procedure were observed to have an impact.