A taxonomic study was carried out on a novel algae-associated bacterial strain Z3-1T, which was isolated from phycosphere microbiota of toxic marine dinoflagellate Alexandrium tamarense 880. Cells of strain Z3-1T were Gram-stain-negative, rod-shaped and strictly aerobic and were motile by means of flagella. Strain Z3-1T grew at 25-42 °C, pH 5.0-10.0 and 1.0-5.0 % (w/v) NaCl. Strain Z3-1T reduced nitrate to nitrite, but did not reduce nitrite to nitrogen gas. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain Z3-1T belongs to the genus Nitratireductor showing the highest sequence similarity (97.0 %) to Nitratireductor basaltis JCM 14935T. The average nucleotide identity and digital DNA-DNA hybridization relatedness between strain Z3-1T and type strains of genus Nitratireductor with available genome sequences were in the ranges of 72.4-74.4 % and 22.7-23.3 %, respectively. The major fatty acids were summed in feature 8 (C18:1 ω7c and/or C18:1 ω6c), C19:0 ω8c cyclo, C18:1 ω7c 11-metyl and iso-C17:0. The major polar lipids were determined as diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, two unidentified phospholipids and four unidentified polar lipids. The genomic DNA G+C content calculated from genome sequence was 65.6 mol%. Based on genotypic, chemotaxonomic and phenotypic data obtained, strain Z3-1T represents a novel species of the genus Nitratireductor, for which the name Nitratireductor alexandrii sp. nov. is proposed with the type strain Z3-1T (=KCTC 62458T=CCTCC AB 2017227T).
Keywords: Alexandrium tamarense; Nitratireductor alexandrii sp. nov; algae-associated bacteria; phycosphere microbiota; toxic marine dinoflagellate.