Nitrosospira lacus sp. nov., a psychrotolerant, ammonia-oxidizing bacterium from sandy lake sediment

A Gram-negative, spiral chemolithotrophic ammonia-oxidizing bacterium, designated APG3T was isolated into pure culture from sandy lake sediment collected from Green Lake, Seattle Washington, USA. Phylogenetic analyses based on 16S rRNA genes showed that strain APG3T belongs to the cluster 0 Nitrosospira, which is presently not represented by described species, with Nitrosospira multiformis (cluster 3) as its closest validated species (identity of 98.6 %). Strain APG3T grows at 4°C but cannot grow at 35°C, indicating that this bacterium is psychrotolerant. Remarkably, the strain was able to grow at a wide range of pH (pH 5-9), which was greater than the range of studied ammonia-oxidizing bacteria in pure culture. The G+C content of the APG3T genome is 53.5%, which is similar to N. multiformis ATCC25196 (53.9%) but higher than that of N. europaea (50.7%) and N. eutropha (48.5%). The average nucleotide identity (ANI) calculated for the genomes of strain APG3T and N. multiformis was 75.45%, a significantly lower value than 95% ANI, which corresponds to 70% species level cut-off based on DNA-DNA hybridization. Overall polyphasic taxonomy study indicated that strain APG3T represents a new species in the genus Nitrosospira for which the name Nitrosospira lacus sp. nov. is proposed (type strain APG3T = NCIMB 14869T = LMG 27536T = ATCC BAA-2542T).