Abstract
Conjugative plasmids play an important role in bacterial evolution by transferring niche-adaptive traits between lineages, thus driving adaptation and genome diversification. It is increasingly clear, however, that in addition to this evolutionary role, plasmids also manipulate the expression of a broad range of bacterial phenotypes. In this review, we argue that the effects that plasmids have on the expression of bacterial phenotypes may often represent plasmid adaptations, rather than mere deleterious side effects. We begin by summarizing findings from untargeted omics analyses, which give a picture of the global effects of plasmid acquisition on host cells. Thereafter, because many plasmids are capable of both vertical and horizontal transmission, we distinguish plasmid-mediated phenotypic effects into two main classes based upon their potential fitness benefit to plasmids: (i) those that promote the competitiveness of the host cell in a given niche and thereby increase plasmid vertical transmission, and (ii) those that promote plasmid conjugation and thereby increase plasmid horizontal transmission. Far from being mere vehicles for gene exchange, we propose that plasmids often act as sophisticated genetic parasites capable of manipulating their bacterial hosts for their own benefit.This article is part of the theme issue ‘The secret lives of microbial mobile genetic elements’.
Highlights
Plasmids are semi-autonomous, self-replicating, non-chromosomal DNA elements that are commonly present in bacterial genomes [1]
— How does plasmid manipulation vary across a broader taxonomic range of bacterial hosts? Most of the studies discussed in this review have focused on gammaproteobacterial hosts
Plasmids can have effects on bacterial phenotypes that extend beyond those conferred by the accessory gene cargo that they encode, by manipulating the expression of genes encoded on the bacterial chromosome
Summary
Plasmids are semi-autonomous, self-replicating, non-chromosomal DNA elements that are commonly present in bacterial genomes [1]. Plasmid accessory genes encode a wide range of ecological functions, including resistance to toxins, metabolic and catabolic capabilities, and production of virulence factors and anticompetitor toxins [13,14] Plasmids enable their bacterial hosts to adapt to environmental stresses, such as antibiotics and toxic metals, or to colonize new niches, for example, through the exploitation of novel substrates or new hosts [8,15,16]. Given this important role in HGT, it is understandable, that most studies of the ecological and evolutionary impact of plasmids have focused on these accessory functions It is becoming increasingly clear, that besides the accessory gene functions they encode, plasmid acquisition alters the expression of a wide range of bacterial phenotypes [11,16,18]. Thereafter, because many plasmids are capable of both vertical and horizontal transmission, we distinguish plasmid-mediated phenotypic effects into two main classes of potential fitness benefit: (i) those that promote the competitiveness of the host cell in a given niche and thereby increase plasmid replication through vertical transmission, and (ii) those that promote plasmid conjugation and thereby increase plasmid replication through horizontal transmission
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