A joint study of the Vall d'Hebron Research Institute (VHIR), the http://ibecbarcelona.eu/ca/" Institute of Bioengineering of Catalonia (IBEC) and the Department of Genetics and Microbiology of the UAB found defects in one of the most commonly used bacteria in microbiology laboratories. The work has been published in journal https://www.nature.com/articles/s41598-017-14051-2" Nature.The PAO1 strain of the Pseudomonas aeruginosa bacteria is used as a reference in most clinical and research laboratories. An essential enzyme for the cell division of PAO1 is the ribonucleotide reductase RNR, which provides the necessary monomers for the synthesis and repair of DNA. P. aeruginosa is one of the few microorganisms that encodes three different classes of RNR in its genome, which allows it to grow and adapt to various environmental conditions, even during the infection, which is why it has become so omnipresent in microbiology laboratories.The researchers discovered that the absence of RNR activity leads to cell elongation in the PAO1 strain, indicating a lack of growth. In addition, the gene expression of RNR during anaerobiosis - processes that occur in the absence of oxygen - differs between the clinical strains of P. aeruginosa and those employed in the laboratory, because RNR class III is much more expressed in isolated clinical P. aeruginosa compared to laboratory strains."It seems that PAO1 has been adapted to laboratory conditions, something like when our bodies become resistant to antibiotics," explains Eduard Torrents, IBEC's principal investigator. During the infection, clinical P. aeruginosa acts in conditions where oxygen is not present, but the PAO1 laboratory strain of P. aeruginosa cannot grow in the same way under these conditions.In this work, it has been identified that a single mutation in the region promoting the class III RNR of the PAO1 strain interrupts its anaerobic transcription, decreasing its virulence. This means that PAO1 is not the suitable strain for research in anaerobic or infectious conditions, nor for the search of new antimicrobial compounds.The discovery was made while new strategies were developed to combat bacterial infections and possible therapeutic targets, which is strongly related to cystic fibrosis.This research has been partially funded by the Spanish Foundation for Cystic Fibrosis and by Obra Social "la Caixa", and carried out by Eduard Torrents, principal investigator at the IBEC and the PhD student Anna Crespo in collaboration with Dr. Joan Gavaldà, coordinator of the Antibiotic Resistance Laboratory of the VHIR's http://bit.ly/2sX0nyF Infectious Diseases Research Group.