Abstract
Describing the role of plasmids and their contribution to the exchange of genetic material among bacteria is essential for understanding the fields of plasmid epidemiology, microbial ecology, and commercial and synthetic microbiology. Broad-host-range (BHR) plasmids are those that are found not only in a single bacterial species, but in members of different taxonomic groups and are of significant interest to researchers in many fields. We applied a novel approach to computationally identify new BHR plasmids, in which we searched for highly similar cognate plasmids within a comprehensive plasmid database. After identifying 125 plasmid groups with highly similar cognates found in multiple taxa, we closely examined BHR plasmids found in multiple families. The majority of our identified BHR plasmids are found in members of the Enterobacteriaceae and closely related taxa, while three BHR plasmids of potential commercial significance were found in two species of Cyanobacteria. One plasmid with an exceptionally broad host range was found in both Gram-positive and Gram-negative bacterial species. This analysis demonstrates the utility of this method in identifying new BHR plasmids while highlighting unknown ranges of previously documented plasmids.
Highlights
Genetic exchange outside of the traditional parent-to-offspring motif is an integral component of environmental adaptation and evolution in bacteria [1], and is often accomplished through the exchange of plasmids [2]
While selfish plasmids have been documented [3], this exchange of genetic material is often associated with benefits to the host as it can lead to the spread of a variety of functions, including degradation of hydrocarbons and anthropogenic toxic waste [4], bacteriocin and toxin production to ward off predators [5], and, alarmingly, antibiotic resistance and virulence plasmids that nullify the effectiveness of antibiotics and lead to novel and untreatable diseases [6]
Since early attempts to explain the host ranges of specific plasmids [7], there have been attempts to define what determines whether a host range, or the variety of micro-organisms a plasmid can be maintained within and actively replicated within [10], can be classified as ‘broad’, ranging from being able to be exchanged between Enterobacteria and Pseudomonas [11], to more broadly being able to cross taxonomic barriers [12]
Summary
Genetic exchange outside of the traditional parent-to-offspring motif is an integral component of environmental adaptation and evolution in bacteria [1], and is often accomplished through the exchange of plasmids [2]. Taking a sequence-based approach to searching for new BHR plasmids, we compiled and examined a comprehensive database of bacterial plasmids to examine their host range.
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