Diversity of chromium-resistant and -reducing bacteria in a chromium-contaminated activated sludge.
OBJECTIVE
This study attempts to establish a relationship between the Cr(VI) resistance of the culturable microbial community and the Cr(VI) resistance and Cr(VI)-reducing ability of representative strains of each population, in order to assess whether these are exclusive characteristics of one microbial group or abilities shared among many groups.


RESULTS
A group of 48 Cr(VI)-resistant isolates, with different colony types, was isolated from chromium-contaminated activated sludge. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis protein patterns and fatty acid methyl ester analysis identified six populations, representing 54% of the isolated bacteria, as belonging to the genera Acinetobacter and Ochrobactrum. The remaining populations included strains identified as species of the beta-Proteobacteria and high G + C Gram-positive bacteria. The Cr(VI) resistance and reduction ability of the strains were tested. All but two isolates grew in the presence of 1 mmol l(-1) Cr(VI). During enrichment, all isolates were able to survive to 2 mmol l(-1) Cr(VI) and complete Cr(VI) reduction was achieved. Representative strains of each population were able to partially reduce (5.4-39.1%) the Cr(VI) present in the growth medium.


CONCLUSIONS
Most of the identified isolates have never been reported to be Cr(VI)-resistant and/or Cr(VI)-reducing strains. The mechanisms of Cr(VI) resistance and reduction may differ from group to group; therefore, it is evident that both Cr(VI) resistance and reduction are shared abilities and not an exclusive characteristic of a single group, possibly reflecting horizontal genetic transfer resulting from selective pressure in this contaminated environment.


CONCLUSIONS
To our knowledge, this is the first study of a microbial community under chronic chromate stress and, as the success of microbial-based metal remediation technologies requires a better understanding of the microbial community and the population response to metal stress, it may contribute to the implementation of a strategy of bioremediation of chromate-contaminated environments.
Francisco
R
R
Instituto do Ambiente e Vida, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Portugal.
Alpoim
M C
MC
Morais
P V
PV
D001419:Bacteria / Q000145:classification* / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry; D002857:Chromium / Q000378:metabolism* / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D005227:Fatty Acids / Q000032:analysis; D007220:Industrial Waste; D008826:Microbial Sensitivity Tests; D010084:Oxidation-Reduction; D010641:Phenotype; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology*; D013633:Tanning
D001426:Bacterial Proteins; D003470:Culture Media; D005227:Fatty Acids; D007220:Industrial Waste; D012722:Sewage; D002857:Chromium