Data from: Antibiotic resistance correlates with transmission in plasmid evolution

Conjugative (horizontally transmissible) plasmids are autonomous
replicators, whose ‘self-interests’ do not necessarily overlap with those
of their hosts. This situation causes plasmids and bacteria to sometimes
experience differing selection pressures. Escherichia coli plasmid pB15
contains genes for resistance to several antibiotics, including
tetracycline. When plasmid-bearing cells were experimentally evolved in
the laboratory, changes in resistance level in the unselected tetracycline
marker coincided with changes in plasmid rates of vertical versus
horizontal transmission. Here we used minimum-inhibitory assays that
measure resistance levels as quantitative traits to determine phenotypic
correlations among plasmid characters and to estimate divergence among
plasmid lineages. Results suggested that plasmid-level evolution led to
formation of two phenotypically-dissimilar groups: virulent (highly
infectious) and avirulent (weakly infectious) plasmids. In contrast,
measures of carbon-source utilization, and fitness assays relative to a
common competitor revealed that bacterial hosts generally converged in
phenotypic performance, despite divergence among their associated
plasmids. Preliminary sequence analyses suggested that divergence in
plasmid conjugation was due to altered configurations of a shufflon region
(a site-specific recombination system), where genetic rearrangements
affect conjugative ability. Furthermore, we proposed that correlated
resistance and transmission in pB15 derivatives were caused by a
tetracycline-resistance transposon inserted into a transfer operon,
allowing transcription from its promoter to simultaneously affect both
plasmid resistance and transmission.