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

To find a biomarker for denitrification in activated sludge, five denitrify ing strains isolated from three wastewater treatment plants were studied. T hese strains were selected from among 1500 isolates for their excellent den itrifying properties. They denitrify quickly and have no lag phase when swi tching from aerobic to anoxic conditions. All strains have the cd(1)-type o f nitrite reductase. The strains are Gram-negative rods and they all grow a s filamentous chains when cultivated in liquid solution. The strains differ in colony morphology when grown on nutrient agar. Almost full-length 16S r DNA sequences were determined and phylogenetic analysis revealed that these strains are positioned among members of the genus Comamonas in the beta -s ubclass of the Proteobacteria. Signature nucleotides and bootstrap percenta ges 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 t heir 16S rDNA sequences, and grouped tightly together in the phylogenetic t ree. Sequence motifs in the 16S rRNA gene were also found, suggesting the m onophyletic origin of these strains. Nevertheless, some strains differed fr om the others, for example strain 110 branches early from the other strains and 5.38g is phenotypically more inert. Therefore, it is proposed that str ains 110, 123(T), 2.99g and P17 are classified into a new species, Comamona s denitrificans sp. nov., while the taxonomic status of strain 5.38g will h ave to await the outcome of further studies. The type strain of Comamonas d enitrificans is 123(T) (ATCC 700936(T)).