bacteria that survive the pollutant mixing conditions of the upper basin of the lerma river (carl) require a specialized metabolism for survival. under this postulation, sediment was taken from three sites of the carl as a source of bacteria resistant to cr+6. at the site identified as lerma, greater variability of species was found in the group of selected bacteria that reduced cr+6. in tultepec, the highest population of cr+6 reducing bacteria was isolated. six strains with different morphological and biochemical characteristics were isolated from the sediments. these strains tolerated concentrations up to 1000 mg l-1 of cr+6 in liquid media. also they reduced cr+6 to cr+3 in percentages between 7 and 40, following 7 days, supplemented with 200 mg l-1 of cr+6. the strains studied were gram negative and showed a minimum inhibitory concentration greater than that found in other studies. the transformation capacity of each strain in descending order were: f, a, b, c, e and d. the kinetics of reduction of strain f showed the highest transformation of cr+6 to cr+3, obtaining a reduction of 33.59 % at 12 days. the biomass of strain f was not affected by the presence of cr+6. it is important to note that the medium itself represented a reduction of cr+6 (17.21 %). the use of the api-20e kit was helpful in determining some biochemical reactions of strains, however, this identification was not conclusive because it presented low percentages of similarity (83.1 to 90.7 %). these strains represent a potential of biotechnology for use in treatment systems to reduce cr+6 to cr+3, and even in trials of other heavy metals.