A novel system of bacterial cell division arrest implicated in horizontal transmission of an integrative and conjugative element

Abstract

Integrative and conjugative elements (ICEs) are widespread mobile DNA elements in the prokaryotic world. ICEs are usually retained within the bacterial chromosome, but can be excised and transferred from a donor to a new recipient cell, even of another species. Horizontal transmission of ICEclc, a prevalent ICE in proteobacteria, only occurs from developed specialized transfer competent (tc) cells in the donor population. tc cells become entirely dedicated to the ICE transmission at the cost of cell proliferation. The cell growth impairment is mediated by two ICEclc located genes, parA and shi, but the mechanistic and dynamic details of this process are unknown. To better understand the function of ParA and Shi, we followed their intracellular behavior from fluorescent protein fusions, and studied host cell division at single-cell level. Superresolution imaging revealed that ParA-mCherry colocalized with the host nucleoid while Shi-GFP was enriched at the membrane during the growth impairment. Despite being enriched at different cellular locations, the two proteins showed in vivo interactions, and mutations in the Walker A motif of ParA dislocalized both ParA and Shi. In addition, ParA mutations in the ATPase motif abolished the growth arrest on the host cell. Time-lapse microscopy revealed that ParA and Shi initially delay cell division, suggesting an extension of the S phase of cells, but eventually completely inhibit cell elongation. The parA-shi locus is highly conserved in other ICEclc-related elements, and expressing ParA-Shi from ICEclc in other proteobacterial species caused similar growth arrest, suggesting that the system functions similarly across hosts. The results of our study provide mechanistic insight into the novel and unique system on ICEs and help to understand such epistatic interaction between ICE genes and host physiology that entails efficient horizontal gene transfer.

An analog to digital converter controls bistable transfer competence development of a widespread bacterial integrative and conjugative element

“…Stochastic modelling suggested that the feedback loop maintains positive output during a longer time period than in its absence (although it will drop to zero at infinite time). Previous experimental data suggested that the tc cells indeed do not return to a silent ICE clc state, but become irreparably damaged, arrest their division ( Takano et al, 2019 ) and wither ( Reinhard et al, 2013 ). However, because their number is proportionally low, there is no fitness cost on the population carrying the ICE ( Delavat et al, 2016 ; Gaillard et al, 2008 ).…”

“…ICE clc transfer competence comprises a differentiated stable state, because initiated tc cells do not transform back to the ICE-quiescent state. Although tc cells divide a few times, their division is compromised by the ICE and eventually arrests completely ( Takano et al, 2019 ; Reinhard et al, 2013 ).…”

Temporal Shifts in Antibiotic Resistance Elements Govern Virus-Pathogen Conflicts

“…Interestingly, infection by a phage that is not restricted by ICEVchInd5 stimulated higher frequency conjugation, while infection by a restricted phage did not. There is an expected energetic cost and accompanying growth delay associated with the formation of the conjugative machinery, as has been shown for other ICEs (52). When infected by a restricted phage, there may be little benefit for SXT ICEs to trigger conjugation, as their host cell may suffer a selective disadvantage limiting the SXT ICE's vertical transmission.…”

An analog to digital converter controls bistable transfer competence development of a widespread bacterial integrative and conjugative element

“…ICEclc transfer competence comprises a differentiated stable state, because initiated tc cells do not transform back to the ICE-quiescent state. Although tc cells divide a few times, their division is compromised by the ICE and eventually arrests completely 13,14 .…”