Acinetobacter baumannii
is an opportunistic bacterium that causes hospital-acquired infections with a high mortality and morbidity, since there are strains resistant to virtually any kind of antibiotic. The chase to find novel strategies to fight against this microbe can be favoured by knowledge of the complete catalogue of genes of the species, and their relationship with the specific characteristics of different isolates. In this work, we performed a genomics analysis of almost 2500 strains. Two different groups of genomes were found based on the number of shared genes. One of these groups rarely has plasmids, and bears clustered regularly interspaced short palindromic repeat (CRISPR) sequences, in addition to CRISPR-associated genes (cas genes) or restriction-modification system genes. This fact strongly supports the lack of plasmids. Furthermore, the scarce plasmids in this group also bear CRISPR sequences, and specifically contain genes involved in prokaryotic toxin–antitoxin systems that could either act as the still little known CRISPR type IV system or be the precursors of other novel CRISPR/Cas systems. In addition, a limited set of strains present a new cas9-like gene, which may complement the other cas genes in inhibiting the entrance of new plasmids into the bacteria. Finally, this group has exclusive genes involved in biofilm formation, which would connect CRISPR systems to the biogenesis of these bacterial resistance structures.
Summary
The presence of pharmaceutical compounds in waters and soils is of particular concern because these compounds can be biologically active, even at environmental concentrations. Most pharmaceutical contaminants result from inefficient removal of these compounds during wastewater treatment. Although microorganisms able to biodegrade pharmaceuticals compounds have been described, the isolation and characterization of new bacterial strains capable of degrading drugs remain important to improve the removal of this pollutant. In this work, we describe the Sphingomonas wittichii strain MPO218 as able to use ibuprofen as the sole carbon and energy source. The genome of MPO218 consists of a circular chromosome and two circular plasmids. Our analysis shows that the largest plasmid, named pIBU218, is conjugative and can horizontally transfer the capability of growing on ibuprofen after conjugation with another related bacterium, Sphingopyxis granuli TFA. This plasmid appears to be unstable since it undergoes different deletions in absence of selection when growth on ibuprofen is not selected. This is the first described example of a natural and conjugative plasmid that enables growth on ibuprofen and is another example of how horizontal gene transfer plays a crucial role in the evolution of bacteria.
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