On the conditions for long term maintenance of plasmids in the environment

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Christidi, Eleni (2022). On the conditions for long term maintenance of plasmids in the environment. University of Birmingham. Ph.D.

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Abstract

Plasmids of all sorts, with various advantages and disadvantages, co-exist in the environment. Many carry genes beneficial to the host under certain conditions yet such genes can be acquired by the chromosome rendering the plasmid superfluous. Despite this, plasmids carrying antibiotic resistance genes have become more prevalent with the use of antibiotics. As plasmids generally cause fitness costs and are not always positively selected, the question of which plasmid characteristics are enabling their persistence under which conditions arises. Contributing to answer this question by using suitable mathematical models was the goal of this thesis. Key findings were that (i) fluctuating environmental conditions only facilitated the maintenance of plasmids that provided local adaptation to their hosts, (ii) broad host-range was advantageous for plasmids in two-species communities while incompatibility facilitated co-existence of narrow host-range plasmids due to a helper effect, (iii) two mechanisms were unlikely to explain the effect of flagella on plasmid spread in biofilms. These findings are consistent with the facts: plasmids often carry genes to provide local adaptation, broad and narrow host-range plasmids, compatible and incompatible plasmids, plasmids with high or low fitness costs and transfer rates co-exist, suggesting that there is no single answer to the question.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):