Microbial Pharmacology and Population Biology (MicroPop)

MicroPop focus on two main topics:

1. Evolution, selection, and spread of antibiotic resistance: It is clear that the frequency of antimicrobial drug resistance in the community is associated with the total level of antimicrobial consumption. Not so clear is the association between reduced consumption levels and subsequent reduction in the frequency of resistance. We focus on different processes that may counteract the reversal of antimicrobial resistance in drug free environments such as the biological cost of resistance, horizontal gene transfer, and genetic stability of resistance determinants. We are currently expanding our activities to include approaches for optimized antimicrobial treatment informed by principles of evolutionary and population biology and the transmission dynamics of antimicrobial resistance genes/elements in bacterial populations.

2. Mechanistic and evolutionary consequences of bacterial recombination: Horizontal gene transfer (HGT) in bacteria plays a major role in adaptive evolution exemplified by the evolution, spread and selection for antibiotic resistance determinants. For two out of three described mechanisms of HGT, conjugation and transduction, gene recruitment through recombination is likely a coincidental byproduct of plasmids’ and phages’ need for continuous transmission to new hosts. The third mechanism of HGT, natural transformation, is a complex mechanism for DNA uptake that requires the concerted action of many chromosomal genes. On first consideration it appears evident that this mechanism for HGT has evolved to “sample the available sequence space” in order to increase the adaptation rates of transformable strains. However, other hypotheses exist for both the evolution and the maintenance of natural transformation in bacteria. We are currently testing a number of these hypotheses both experimentally and theoretically. We are also interested in the mechanistic basis of bacterial recombination and how it affects genetic diversity in microbes.


MicroPop closely collaborates and shares lab-space and facilities at the Department of Pharmacy with the Infection Biology research group, headed by Dr. Soren Abel (Centre for Molecular Medicine Norway). 

Selected Publications:

Di Luca MC., Sørum V., Starikova I., Klos J., Hülter N., Naseer U., Johnsen PJ., Samuelsen Ø. Low biological cost of carbapenemase producing plasmids following transfer from Klebsiella pneumonia to Escherichia coli. J Antimicrob Chemother2017 Jan;72(1):85-89. 

Harms K., Lunnan A.,Hülter N., Mourier T., Vinner L., Andam C.P., Marttinen P., Fridholm H., Hansen A.J.,  Hanage W.P., Nielsen K.M., Willerslev E., Johnsen P.J. Substitutions of short heterologous DNA segments of intra- or extragenomic origins produce clustered genomic polymorphisms. Proc Natl Acad Sci U S A. 2016 Dec 27;113(52):15066-15071.

Engelstädter J., Harms K., Johnsen PJ. The evolutionary dynamics of integrons in changing environments ISME J, 2016, Jun;10(6):1296-307.

Ambur OH., Engelstädter J., Johnsen PJ., Miller EL., Rozen DE. Steady at the wheel: conservative sex and the benefits of natural transformation. Philos Trans R Soc Lond B Biol Sci. 2016 Oct 19;371(1706). pii: 20150528

Utnes A., Sorum V., Hulter N., Primicerio R., Kloos J., Nielsen K.M., andP. J. Johnsen. Growth phase specific evolutionary benefits of natural transformation in Acinetobacter baylyi.  ISME J, 2015;advance online publication 7 April 2015; doi: 10.1038/ismej.2015.35

Levin B. R., Baquero F., and P. J. Johnsen. A Model-Guided Analysis and Perspective on the Evolution and Epidemiology of Antibiotic Resistance and its Future. Current Opin Microbiol. 2014: Jun;19:83-9.

Overballe-Petersen S., Harms K*., Orlando L. A., Mayar J. V., Rasmussen S., Dahl T. W., Rosing M. T., Poole A. M., Sicheritz-Ponten T., Brunak S., Inselmann S., de Vries J., Wackernagel W., Pybus O. G., Nielsen R., Johnsen P. J., Nielsen K. M., and Willerslev E. Bacterial natural transformation by highly fragmented and damaged DNA. Proc Natl Acad Sci U S A. 2013: 110(49):19860-5. doi: 10.1073/pnas.1315278110. Epub 2013 Nov 18

Starikova I., Al-Haroni M., Werner G., Roberts A. P., Sørum V., Nielsen K.M.,  and P. J. Johnsen. * Fitness costs of mobile genetic elements in Enterococcus faecium and Enterococcus faecalis.J Antimicrob Chemother. 2013 Dec;68(12):2755-65. Epub 2013 Jul 5.

StarikovaI., Harms K., Lunde T. M., Haugen P., Primicerio R., Samuelsen Ø., Nielsen K. M, and P. J. Johnsen. 2012. A trade-off between the fitness cost of functional integrases and long-term stability of integrons. PloS Pathog.8(11):e1003043.

Group members:

Pål J. Johnsen, Professor and group leader

Raul Primicerio, Associate Professor

Ørjan Samuelsen, Professor (20%) and Norwegian National Advisory Unit on Detection of Antimicrobial Resistance, University Hospital of North Norway.

Elizabeth Aarag Fredheim, Scientist and Lab Manager


Nicole Podnecky, Postdoctoral Fellow

Maria Chiara de Luca, Postdoctoral Fellow

Klaus Harms, Researcher/Research associate

Vidar Sørum, Postdoctoral Fellow

Julia Kloos, PhD student

Tracy T. M. Lunde, PhD student

Emma Lu Øynes, Medical Student Research Programme

Jessica N. Tran, Master of Pharmacy student

Former Group Members:

Dr. Nils Hülter

Dr. Irina Starikova

Dr. Ane Utnes

Mikkel Meyn Liljegren, Msc

Kristina B. Pedersen, Msc

Asbjørn Lunnan, Msc

Lilli Nguyen, Msc

Jonathan Nguyen, Msc

Gina Pat, Msc

Mari Norvik, Msc

Joachim Hegstad, Msc

Tammy Nguyen, Msc

Cho Kit Lam, Msc

Sanne E. Valla, Msc

Camilla R. Hasund, Msc 

Christopher Fröhlich, Erasmus+ student


Pål J. Johnsen

Dept. Pharmacy

University of Tromsø,

N-9037 Tromsø,




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