Effect of chemotherapeutic agents on natural transformation frequency in Acinetobacter baylyi.

Natural transformation is the ability of a bacterial cell to take up extracellular DNA which is subsequently available for recombination into the chromosome (or maintenance as an extrachromosomal element). Like other mechanisms of horizontal gene transfer, natural transformation is a significant driver for the dissemination of antimicrobial resistance. Recent studies have shown that many pharmaceutical compounds such as antidepressants and anti-inflammatory drugs can upregulate transformation frequency in the model species Acinetobacter baylyi. Chemotherapeutic compounds have been shown to increase the abundance of antimicrobial resistance genes and increase colonization rates of potentially pathogenic bacteria in patient gastrointestinal tracts, indicating an increased risk of infection and providing a pool of pathogenicity or resistance genes for transformable commensal bacteria. We here test for the effect of six cancer chemotherapeutic compounds on A. baylyi natural transformation frequency, finding two compounds, docetaxel and daunorubicin, to significantly decrease transformation frequency, and daunorubicin to also decrease growth rate significantly. Enhancing our understanding of the effect of chemotherapeutic compounds on the frequency of natural transformation could aid in preventing the horizontal spread of antimicrobial resistance genes.

Testing for the fitness benefits of natural transformation during community-embedded evolution.

Natural transformation is a process where bacteria actively take up DNA from the environment and recombine it into their genome or reconvert it into extra-chromosomal genetic elements. The evolutionary benefits of transformation are still under debate. One main explanation is that foreign allele and gene uptake facilitates natural selection by increasing genetic variation, analogous to meiotic sex. However, previous experimental evolution studies comparing fitness gains of evolved transforming- and isogenic non-transforming strains have yielded mixed support for the 'sex hypothesis.' Previous studies testing the sex hypothesis for natural transformation have largely ignored species interactions, which theory predicts provide conditions favourable to sex. To test for the adaptive benefits of bacterial transformation, the naturally transformable wild-type Acinetobacter baylyi and a transformation-deficient ∆comA mutant were evolved for 5 weeks. To provide strong and potentially fluctuating selection, A. baylyi was embedded in a community of five other bacterial species. DNA from a pool of different Acinetobacter strains was provided as a substrate for transformation. No effect of transformation ability on the fitness of evolved populations was found, with fitness increasing non-significantly in most treatments. Populations showed fitness improvement in their respective environments, with no apparent costs of adaptation to competing species. Despite the absence of fitness effects of transformation, wild-type populations evolved variable transformation frequencies that were slightly greater than their ancestor which potentially could be caused by genetic drift.

Collection of Annotated Acinetobacter Genome Sequences.

The genus Acinetobacter contains environmental species as well as opportunistic pathogens of humans. Several species are competent for natural transformation, an important mechanism of horizontal gene transfer. Here, we present the genome sequences of 19 Acinetobacter strains used in past and upcoming studies of natural transformation.

Antimicrobial resistance acquisition via natural transformation: context is everything.

Natural transformation is a process where bacterial cells actively take up free DNA from the environment and recombine it into their genome or reconvert it into extra-chromosomal genetic elements. Although this mechanism is known to mediate the uptake of antibiotic resistance determinants in a range of human pathogens, its importance in the spread of antimicrobial resistance is not always appreciated. This review highlights the context in which transformation takes place: in diverse microbiomes, in interaction with other forms of horizontal gene transfer and in increasingly polluted environments. This examination of the abiotic and biotic drivers of transformation reveals that it could be more important in the dissemination of resistance genes than is often recognised.