Native Plasmids of Amino Acid–Producing Corynebacteria

Authored by: A. Tauch

Handbook of Corynebacterium glutamicum

Print publication date:  March  2005
Online publication date:  March  2005

Print ISBN: 9780849318214
eBook ISBN: 9781420039696
Adobe ISBN:

10.1201/9781420039696.ch4

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Abstract

Plasmids are extrachromosomal DNA elements that replicate in an autonomous, self-controlled way and that exist with characteristic copy numbers within a host organism [7,10]. They are mostly organized as double-stranded circular DNA molecules with closed strands that can be isolated in the form of supercoiled DNA. Concerning their genetic organization, plasmids contain an essential DNA region, the basic replicon, which comprises the genes and loci involved in autonomous replication and replication control. Additionally, plasmids may encode auxiliary inheritance mechanisms ensuring their stable maintenance and faithful segregation during cell division [18,15]. Plasmids may also carry genes that could be considered dispensable, although they might play an important or beneficial role for the plasmid itself and/or its host organism. Furthermore, plasmids favor the genetic exchange in bacterial populations since they cannot only incorporate, but also deliver additional genetic material by recombination processes or transposition. This so-called gene load may be involved, for instance, in antibiotic or toxic heavy metal resistance or it may confer favorable physiological traits on the host [68]. Since plasmids can be introduced into new host species by a variety of transfer mechanisms, they can be considered to represent an easy, accessible pool of horizontal mobile DNA, which is shared among bacterial populations. Consequently, plasmids play a major role in enhancing the genetic diversity and adaptation of bacteria by transferring their gene load into new host species [31].

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