Degradation of low-ethoxylated nonylphenols by a Stenotrophomonas strain and development of new phylogenetic probes for Stenotrophomonas spp. detection.

An aerobic bacterium (BCc6), isolated from nonylphenol polyethoxylates (NPEOs) contaminated sludge, was shown to be capable of degrading low-ethoxylated NPEO mixtures. Sequencing of 16S rRNA gene (rDNA) showed that it clustered with Stenotrophomonas nitritireducens, positioned in the gamma class of the Proteobacteria phylum. Fluorescent in situ hybridisation (FISH), performed on BCc6 strain and on the previously isolated Stenotrophomonas BCaL2, also involved in NPEO degradation but clustering with Stenotrophomonas maltophilia, showed that strain BCc6 did not hybridise with the phylogenetic probe specific for S. maltophilia, whose target is a 19 bp region of the 16S rRNA. Furthermore, none of the two strains hybridised with phylogenetic probes targeted to a 17 bp region of the 23S rRNA, which corresponds to the site identifying the Gammaproteobacteria class. rDNA Analyses performed on the two strains evidenced two new polymorphisms, the first-one at the 23S rRNA Gammaproteobacteria site, characterising the known members of the Stenotrophomonas genus, the other-one at the 16S rRNA level, characteristic of S. nitritireducens. Two new FISH probes were designed accordingly, tested on control bacterial cultures and employed for in situ monitoring of Stenotrophomonas representatives.