Mixing of Two Microbial Consortia in the Search for Stimulating Chromium Depletion.

Two bacterial consortia (C55 and C33), obtained from an industrial residue contaminated with hexavalent chromium (Cr(VI)), were used to study the behavior of their mixture for depleting this ion in liquid media. In the absence of Cr(VI), C55 showed a greater growth rate than C33, while the latter exhibited biofilm formation. In the presence of this ion, C55 showed resistance up to 800 mg·L^-1 and an ability to diminish up to 400 mg·L^-1 of the Cr(VI) from the medium, while for C33, these concentrations were 400 and 200 mg·L^-1, respectively. Bacterial synergism between these consortia was evaluated using different compound ratios (C55:C33 ratios of 1:1, 1:2, and 2:1), growing at 50, 100, and 200 mg·L^-1 Cr(VI). The best half-lives of Cr(VI) decrease were 16, 31, and 98 h, respectively, for the 1:1 mixture. The ability of C33 and the mixed consortia to form biofilms was verified. MiSeq sequencing revealed 4 major populations for C55 (in a total of 14) and 3 for C33 (8), most of which were common. After an isolation process, 2 bacterial strains were obtained from C55 and 4 from C33. Three of these strains (QRePLB33E, similar to Oceanobacillus profundus; QRePLB33G, to Shouchella clausii; and QRePLB55C, to Cellulosimicrobium funkei) showed resistance to Cr(VI) and the ability to remove 100% of it at least up to 300 mg·L^-1. Thus, synergism between different bacterial consortia obtained from the same site is possible and can improve, by complementing their capacities, both the growth rate and the ability to diminish the xenobiotic from the medium.