A Minority Population of Non-dye-decolorizing Bacillus subtilis enhances the Azo Dye-decolorizing Activity of Enterococcus faecalis.

Microbes live in communities in biological wastewater treatment plants and in the intestines. However, limited information is currently available on the mechanisms by which minority bacterial populations assist other bacteria besides syntrophic relationships as well as on the microbial food web. Therefore, the present study investigated the effects of non-dye-decolorizing Bacillus subtilis strain S4ga at population levels ranging between 0.04 and 4% on the activity of dye-decolorizing Enterococcus faecalis strain T6a1 using a dye decolorization assay. The results obtained revealed that the minority population of B. subtilis S4ga enhanced the dye-decolorizing activity of E. faecalis T6a1, resulting in a shorter lag time and longer active time of dye decolorization. These effects were related to redox potential values rather than O2 concentrations. Comparisons of the extracellular metabolites in individual incubations of E. faecalis T6a1 and B. subtilis S4ga and a co-incubation suggested a mutual relationship through the cross-feeding of specific amino acids (tyrosine, methionine, tryptophan, phenylalanine, valine, and leucine from B. subtilis S4ga to E. faecalis T6a1; glutamine, histidine, aspartic acid, and proline from E. faecalis T6a1 to B. subtilis S4ga). An ana-lysis of intracellular primary metabolites indicated that the arginine deiminase (ADI) pathway, an ATP-producing energy-generating process, was more strongly activated in co-incubated E. faecalis T6a1 than in E. faecalis T6a1 incubated alone. These results suggest that a co-incubation with B. subtilis S4ga promoted ATP production by E. faecalis T6a1 cells and enhanced its dye-decolorizing activity.

Long-term natural remediation process in textile dye-polluted river sediment driven by bacterial community changes.

The textile and dyeing industries are major sources of environmental water pollution all over the world. The textile wastewater effluents discharged into rivers often appear dark red-purple in color due to azo dyes, which can be transformed into carcinogenic aromatic amines. The chemicals used in dyeing are not readily degraded in nature and thus precipitate in river sediment. However, little is known about how dyeing chemicals affect river sediment and river water or how long they persist because they are difficult to monitor. To assess undetectable dyes and byproducts in river sediments, we evaluated the potential of river sediment bacteria to degrade dyes and aromatic amines. We describe the natural remediation of river sediment long-contaminated by textile dyeing effluent. After cessation of wastewater discharge, the dye-degradation potential decreased, and the aromatic amine-degradation potential increased initially and then declined over time. The changes in degradation potential were consistent with changes in the sediment bacterial community. The transition occurred on the order of years. Our data strongly suggest that dyes remained in the river sediment and that aromatic amines were produced even in transparent- and no longer colored-river water, but these chemicals were degraded by the changing sediment bacteria. Time-course monitoring of the degradation activities of key bacteria thus enables assessment of the fate of dye pollutants in river sediments.