Degradation of azo dyes containing aminonaphthol by Sphingomonas sp strain1CX

Sphingomonas sp strain 1 CX was isolated from a wastewater treatment plant and is capable of aerobically degrading a suite of azo dyes, using them as a sole source of carbon and nitrogen. All azo dyes known to be decolorized by strain 1CX (Orange II, Acid Orange 8, Acid Orange 10, Acid Red 4, and Ac id Red 88) have in their structure either 1-amino-2-naphthol or 2-amino-1-n aphthol. In addition, an analysis of the structures of the dyes degraded su ggests that there are certain positions and types of substituents on the az o dye which determine if degradation will occur. Growth and dye decolorizat ion occurs only aerobically and does not occur under fermentative or denitr ification conditions. The mechanism by which 1CX decolorizes azo dyes appea rs to be through reductive cleavage of the azo bond. In the case of Orange II, the initial degradation products were sulfanilic acid and 1-amino-2-nap hthol. Sulfanilic acid, however, was not used by 1CX as a growth substrate. The addition of glucose or inorganic nitrogen inhibited growth and decolor ation of azo dyes by 1CX. Attempts to grow the organism on chemically defin ed media containing several different amino acids and sugars as sources of nitrogen and carbon were not successful. Phylogenetic analysis of Sphingomo nas sp strain 1CX shows it to be related to, but distinct from, other azo d ye-decolorizing Sphingomonas spp strains isolated previously from the same wastewater treatment facility.