Question

The function of conjugativ plasmid is specifid by

Answer 1

Comparative whole-genome analyses have demonstrated that horizontal gene transfer (HGT) provides a significant contribution to prokaryotic genome innovation. The evolution of specific prokaryotes is therefore tightly linked to the environment in which they live and the communal pool of genes available within that environment. Here we use the term supergenome to describe the set of all genes that a prokaryotic ‘individual’ can draw on within a particular environmental setting. Conjugative plasmids can be considered particularly successful entities within the communal pool, which have enabled HGT over large taxonomic distances. These plasmids are collections of discrete regions of genes that function as ‘backbone modules’ to undertake different aspects of overall plasmid maintenance and propagation. Conjugative plasmids often carry suites of ‘accessory elements’ that contribute adaptive traits to the hosts and, potentially, other resident prokaryotes within specific environmental niches. Insight into the evolution of plasmid modules therefore contributes to our knowledge of gene dissemination and evolution within prokaryotic communities. This communal pool provides the prokaryotes with an important mechanistic framework for obtaining adaptability and functional diversity that alleviates the need for large genomes of specialized ‘private genes’.

INTRODUCTION

Bacteria and Archaea display immense genetic and functional diversity, which has facilitated the shaping of the Earth's biosphere during the past 3.8 billion years (Smets & Barkay 2005). They have evolved an array of efficient genome modification mechanisms that allow adaptation to ever-changing environmental conditions, permitting the colonization of a plethora of ecological niches. Unlike eukaryotes, genetic exchange and proliferation in prokaryotes are independent processes (Levin & Bergstrom 2000). This in turn means that apart from direct mutational changes, variation is not automatically introduced by virtue of self-proliferation (vertical transfer), which corresponds to binary fission in prokaryotes. Their genomes are modified by gene loss and by gene addition through duplication and the acquisition of new genes through horizontal gene transfer (HGT).