Selection of bacterial communities linked with late succession stages in nonylphenol ethoxylate-degrading activated sludge

MARIANA LOZADA; EVA L. M. FIGUEROLA; RAÚL F. ITRIA

La Plata, Argentina

Congreso; Segundo Congreso Argentino de Microbiología General; 2005

Sociedad Argentina de Microbiología General

We have analyzed the ecology of bacterial communities associated with nonylphenol polyethoxylate (NPE) biodegradation in laboratory-scale activated sludge. Four replicate lab-scale reactors were built and operated in a fill-and-draw mode, showing stable performance for a period of 21 months. All four reactors were fed with synthetic sewage, and two of them received additionally 1% NPE. The marked differences between treated and control reactors, both in floc structure and in NPE degradation capability suggested the selection of a microbial community specialized in surfactant degradation. The dynamics and community compostion of bacteria in the reactors sludge was analyzed using culture-independent methods, based on ribosomal RNA gene sequences (DGGE, cloning and  library construction, membrane hybridization, fluorescence in situ hybridization and quantitative real time PCR). Distinct populations of bacteria, which were not detected in control reactors, were selected in both replicate NPE-amended reactors, and persisted until the end of the experiment. Dominant populations in NPE-amended reactors were related to not-yet-cultured members of the Gammaproteobacteria,  Acidobacteria, the genus Sphingomonas (a member of the Alphaproteobacteria) and to geni of uncertain taxonomic position within the order Burkholderiales (of the Betaproteobacteria). None of these populations were related to bacteria previously found in culture-dependent studies using with NPE as a sole carbon source. Their phylogenetic affiliation and their difficulty to grow in synthetic media suggest a specialization strategy which is known to occur in late succession stages of ecosystems.