Phylogeny and identification in situ of Nevskia ramosa

An enrichment of the neuston bacterium Nevskia ramosa was investigated by the cultivation-independent rRNA approach. N. ramosa was first described by Famintzin in 1892 as a rod-shaped, slightly bent bacterium forming typical flat rosettes on the surface of shallow freshwater habitats by unilateral slime formation. PCR in combination with cloning and sequencing was used for retrieving 21 partial and 5 nearly full-length 16S rRNA sequences forming three tight clusters. In situ hybridization with rRNA-targeted oligonucleotide probes allowed us to assign the three sequence clusters to three distinct bacterial populations abundant in the enrichment. The two probes that unambiguously identified the N. ramosa morphotype were derived from a 16S rRNA sequence that had similarities of 87.9 to 88.9% to the rRNA sequences of the most closely related group in the database, Xanthomonas sp. and relatives. N. ramosa currently is the only representative of an independent, deep branch of the gamma subclass of the class Proteobacteria. The two other populations abundant in the enrichment were affiliated with the alpha subclass of the class Proteobacteria. They were most closely related to Blastobacter sp. (97.2% similarity) and Mycoplana bullata (97.6% similarity) and might represent new species in the respective genera.