The conjugation window in an Escherichia coli K-12 strain with an IncFII plasmid

Authors: Headd, Brendan; Bradford, Scott

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2020
Publication Date: 8/18/2020
Citation: Headd, B.J., Bradford, S.A. 2020. The conjugation window in an Escherichia coli K-12 strain with an IncFII plasmid. Applied and Environmental Microbiology. 86(17). Article e00948-20. https://doi.org/10.1128/AEM.00948-20.
DOI: https://doi.org/10.1128/AEM.00948-20

Interpretive Summary: Numerous studies have examined the role conjugation plays in the dissemination of antibiotic resistant plasmids in bacteria. However, most studies have only examined conjugation in batch cultures of growing bacteria. The result is there is a gap in knowledge as to when conjugation occurs and why conjugation stops after only several hours. We examined conjugation in E. coli in both growing and non-growing cultures and found that conjugation occurs after the cells have divided and before they have transitioned into a non-growing phase. As a result, conjugation only takes place during a narrow window of time. The significance of this conjugation window is that only a small percentage of bacteria are actually capable of conjugating at any given time and after just a few hours conjugation ceases because of a lack of capable donor cells . In addition, not all recipients of conjugative plasmids can become donor cells due to molecular regulatory controls that prevent conjugation from taking place and recipient cells not being in the correct growth phase. Published models of conjugation do not take these factors into account. We present a computer model that accurately describes conjugation behavior in E. coli.

Technical Abstract: Many studies have examined the role that conjugation plays in disseminating antibiotic resistance genes in bacteria. However, relatively little research has quantitively examined and modeled the dynamics of conjugation under growing and nongrowing conditions beyond a couple of hours. We therefore examined growing and nongrowing cultures of Escherichia coli over a 24-h period to understand the dynamics of bacterial conjugation in the presence and absence of antibiotics with pUUH239.2, an IncFII plasmid containing multiantibiotic- and metal-resistant genes. Our data indicate that conjugation occurs after E. coli cells divide and before they have transitioned to a nongrowing phase. The result is that there is only a small window of opportunity for E. coli to conjugate with pUUH239.2 under both growing and nongrowing conditions. Only a very small percentage of the donor cells likely are capable of even undergoing conjugation, and not all transconjugants can become donor cells due to molecular regulatory controls and not being in the correct growth phase. Once a growing culture enters stationary phase, the number of capable donor cells decreases rapidly and conjugation slows to produce a plateau. Published models did not provide accurate descriptions of conjugation under nongrowing conditions. We present here a modified modeling approach that accurately describes observed conjugation behavior under growing and nongrowing conditions.