Genetic analysis of a plasmid-encoded, host genotype-specific enhancement of bacterial fitness

Abstract

In the absence of antibiotics, carriage of pACYC184 reduces the competitive fitness of an Escherichia coli B genotype that was not previously selected for plasmid carriage, relative to that of an isogenic plasmid-free competitor. However, a host genotype propagated with the plasmid for 500 generations evolved an unexpected competitive advantage from plasmid carriage, relative to its own isogenic plasmid-free segregant. We manipulated the pACYC184 genome in order to identify the plasmid-encoded function that was required for the enhancement of the coevolved host genotype's competitive fitness.

Enhancement of bacterial competitive fitness by apramycin resistance plasmids from non-pathogenicEscherichia coli

“…Although plasmid pUK2002 carries a tetracycline resistance determinant (tetB), plasmid pUK2003 also has this gene but does not confer a fitness advantage. Therefore, in contrast to the results of Lenski et al (1994) it is unlikely that this tetracycline resistance gene plays a significant role in the conferred fitness of these two plasmids. In summary, this is the first identification of natural plasmids isolated from commensal organisms able to confer a fitness advantage on a new host.…”

“…Therefore, a reduction in antibiotic use could result in a decrease in the prevalence of corresponding resistance determinants. Yet resistance plasmids that confer a fitness advantage on their host bacterium have been reported (Lenski et al 1994;Enne et al 2004;Dionisio et al 2005). The detection of antibiotic resistance plasmids capable of enhancing bacterial fitness is of concern.…”

Selection and fitness in bacteriocin–producing bacteria

“…It can be clearly seen that a number of factors may in fact reduce, eliminate, or perhaps reverse the costs associated with bacteriocin production and plasmid carriage. In particular, the likelihood of the coevolution of non-conjugative bacteriocin-encoding plasmids and their hosts to beneficial associations is high (Modi & Adams 1991 ;Lenski et al 1994). Furthermore, any of the bacteriocin burden-reducing features, or any combination of them, may act synergistically within a single bacteriocinproducing strain.…”

“…plasmid-host relationships which are new and in which no history of association between the plasmid and the host exists (Adams et al 1979 ;Helling et al 1981 ;Noack et al 1981 ;Hartl et al 1983 ;Seo et al 1985 ;Nguyen et al 1989). It has been demonstrated, however, that a longterm history of association between plasmids and their hosts may result in beneficial coevolutionary changes in both the plasmid and the host (Bouma & Lenski 1988 ;Lenski et al 1994). In such cases, plasmid carriage no longer imposes a burden on the host, and will in fact result in enhanced fitness of the host relative to the same host after plasmid-curing (Lenski et al 1994).…”

“…It has been demonstrated, however, that a longterm history of association between plasmids and their hosts may result in beneficial coevolutionary changes in both the plasmid and the host (Bouma & Lenski 1988 ;Lenski et al 1994). In such cases, plasmid carriage no longer imposes a burden on the host, and will in fact result in enhanced fitness of the host relative to the same host after plasmid-curing (Lenski et al 1994). Since bacteriocins are widely distributed among bacterial strains and many bacteriocin-encoding plasmids are non-conjugative, it is likely that many of these plasmid-host relationships are long-term.…”