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Sociobiological Control of Plasmid copy number

Mukta Watve¹ & Milind Watve²

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1. Department of Microbiology, Abasaheb Garware college
2. Department of Microbiology,Abasaheb Garware college

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Document Type:

Poster

Date:

Received 26 June 2008 07:28 UTC; Posted 26 June 2008

Subjects:

Evolutionary Biology and Ecology, Microbiology

Tags:

• Multilevel selection
• plasmid
• simulation
• sociobiology
• Bacteria
• gene
• Evolution

Abstract:

Background:
All known mechanisms and genes responsible for the regulation of plasmid replication lie with the plasmid rather than the chromosome. It is possible therefore that there can be copy-up mutants. Copy-up mutants will have within host selective advantage. This would eventually result into instability of bacteria-plasmid association. In spite of this possibility low copy number plasmids appear to exist stably in host populations. We examined this paradox using a computer simulation model.

Model:
Our multilevel selection model assumes a wild type with tightly regulated replication to ensure low copy number. A mutant with slightly relaxed replication regulation can act as a “cheater” or “selfish” plasmid and can enjoy a greater within-host-fitness. However the host of a cheater plasmid has to pay a greater cost. As a result, in host level competition, host cell with low copy number plasmid has a greater fitness. Furthermore, another mutant that has lost the genes required for conjugation was introduced in the model. The non-conjugal mutant was assumed to undergo conjugal transfer in the presence of another conjugal plasmid in the host cell.

Results:
The simulatons showed that if the cost of carrying a plasmid was low, the copy-up mutant could drive the wild type to extinction or very low frequencies. Consequently, another mutant with a higher copy number could invade the first invader. This process could result into an increasing copy number. However above a certain copy number within-host selection was overcompensated by host level selection leading to a rock-paper-scissor (RPS) like situation. The RPS situation allowed the coexistence of high and low copy number plasmids. The non-conjugal “hypercheaters” could further arrest the copy numbers to a substantially lower level.

Conclusions:
These sociobiological interactions might explain the stability of copy numbers better than molecular mechanisms of replication regulation alone.

Presented at:

ASM 108th General Meeting, Boston, 02 June 2008

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License:

This document is licensed to the public under the Creative Commons Attribution 3.0 License

How to cite this document:

Watve, Mukta and Watve, Milind. Sociobiological Control of Plasmid copy number. Available from Nature Precedings <http://dx.doi.org/10.1038/npre.2008.2016.1> (2008)

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