Comamonas denitrificans sp nov., an efficient denitrifying bacterium isolated from activated sludge

To find a biomarker for denitrification in activated sludge, five denitrifying strains isolated from three wastewater treatment plants were studied. These strains were selected from among 1500 isolates for their excellent denitrifying properties. They denitrify quickly and have no lag phase when switching from aerobic to anoxic conditions. All strains have the cd(1)-type of nitrite reductase. The strains are Gram-negative rods and they all grow as filamentous chains when cultivated in liquid solution. The strains differ in colony morphology when grown on nutrient agar. Almost full-length 16S rDNA sequences were determined and phylogenetic analysis revealed that these strains are positioned among members of the genus Comamonas in the beta -subclass of the Proteobacteria. Signature nucleotides and bootstrap percentages were also analysed to verify this position. Strains 110, 123(T), 2.99g, 5.38g and P17 were less than or equal to 96.7 % similar to known strains, but greater than or equal to 99.7 % similar to each other, as judged from their 16S rDNA sequences, and grouped tightly together in the phylogenetic tree. Sequence motifs in the 16S rRNA gene were also found, suggesting the monophyletic origin of these strains. Nevertheless, some strains differed from the others, for example strain 110 branches early from the other strains and 5.38g is phenotypically more inert. Therefore, it is proposed that strains 110, 123(T), 2.99g and P17 are classified into a new species, Comamonas denitrificans sp. nov., while the taxonomic status of strain 5.38g will have to await the outcome of further studies. The type strain of Comamonas denitrificans is 123(T) (ATCC 700936(T)).