Nitratireductor aquibiodomus gen. nov., sp nov., a novel alpha-proteobacterium from the marine denitrification system of the Montreal Biodome (Canada)

The Montreal Biodome operates a methanol-fed denitrification system that treats the water in its three million litre marine mesocosm. An unknown bacterium, named strain NL21(T), was isolated from this system on TSA and R2A agar. The organism is a Gram-negative, rod-shaped (1 x 3 mum) facultative aerobe. Optimal growth conditions on R2A agar are 30-35 degreesC, pH 7-7(.)5 and 1 % (w/w) NaCl. Phylogenetic analysis of the 16S rDNA sequence reveals that strain NL21(T) forms a novel lineage in the family 'Phyllobacteriaceae' within the alpha2 subgroup of the Proteobacteria. The closest related genera are Aminobacter, Pseudaminobacter, Mesorhizobium and Defluvibacter. Major cellular fatty acids are C(18 : 1)omega7c (75 %), C(19 : 0)omega8c cyclopropane (9(.)4 %) and C-18 : 0 (4(.)2 %). The DNA G + C content of strain NL21(T) (57 mol%) differs from those of all other described members of the 'Phyllobacteriaceae' (60-64 mol%). Strain NL21(T) reduces nitrate to nitrite, but does not reduce nitrite to nitrogen gas. Only a few sugars and amino acids can serve as carbon sources. Strain NL21(T) is able to grow without salt and tolerates up to 5 % NaCl. Phylogenetic analysis, as well as physiological and biochemical tests, showed that strain NL21(T) was different from all other members of the 'Phyllobacteriaceae' with validly published names. Strain NL21(T) therefore represents a novel genus, for which the name Nitratireductor aquibiodomus gen. nov., sp. nov. is proposed, with the type strain NL21(T) (= DSM 15645(T) =ATCC BAA-762(T)).