Bacterial Species Diversity and Dye Decolorization of a Two-Species Mixed Consortium

Abstract

This study provides a first attempt to put forward, in terms of information entropy and species diversity, community interactions between decolorizers and nondecolorizers from an ecological engineering perspective. The novelty emphasizes that a species with nonessential functions in mixed cultures still plays a crucial role as a "keystone species" to influence treatment performance. Although nondecolorizers were considered metabolically "dormant" in this model binary-biosystem, their presence still significantly enhanced decolorization performance of decolorizers. The initial and maximal specific decolorization rate are optimal at 50 and 25% Pseudomonas luteola in microbial consortia, respectively. The presence of Escherichia coli DH5α increased the decolorization efficiency of P. luteola even though DH5α was considered "dormant" in this microbial community. In addition, extracellular metabolites expressed by DH5α stimulate decolorization activity of P. luteola. In CSTR, when dye concentration was at less toxic levels (<ca. 500 ppm), steady-state species ecology almost maintained at a ratio of one viable P. luteola to one DH5α cell (i.e., maximal diversity H_max = 1.0). A significant decrease in information entropy (i.e., H_ave = 0.84) and large fluctuations in viable P. luteola cell counts at 1,000 ppm indicated longer response times required for dye stress (or toxicity) at higher levels, and thus an uneven distribution in the community between species was reflected. Mutualism instead of competition between two species is very likely as a driving force directing species evolution to achieve maximal diversity of community as well as to maintain total survival of all species. It is concluded that the diversity of ecological communities potentially influences critical metabolic functions of species in a treatment system.