Ranking of 38 prokaryotes according to their uranium uptake capacity in aqueous solutions: an approach from order theory through the Hasse diagram technique

Uranium contamination is of global concern and several approaches have been applied to cleanse U-contaminated ecosystems. Among them, biotechnological techniques using microorganisms have proven to be eco-friendly. However, knowing which of them behave better for U trapping is still an open question. In this study, a general and a detailed comparison of prokaryotes, differentiated by growth and U uptake conditions, was performed. The general comparison was run over 38 species characterized by different conditions and a subset of 18 bacteria having equal conditions was compared in detail. In both cases, the species were characterized by their percentage of U removal, uptake capacity, and time required for removing U. The methodology used was the Hasse diagram technique, suitably adjusted to address the issue of ordering objects (microorganisms) whose attributes contain interval values. Microorganisms were ranked and a stable top-five of bacteria for U trapping from aqueous systems was obtained: Bacillus licheniformis ATCC 14580, Bacillus mucilaginosus ACCC 10012, Pseudomonas MGF-48, Streptomyces sp., and Pseudomonas sp. EPS-5028. The results show that neither the Gram nor the taxonomic classification determines uptake capacity for the species studied. The method here described can be further applied to other attributes of relevance for the selection of optimal microorganisms, e.g. economical ones.