A bistable prokaryotic differentiation system underlying development of conjugative transfer competence

Abstract

The mechanisms and impact of horizontal gene transfer processes to distribute gene functions with potential adaptive benefit among prokaryotes have been well documented. In contrast, little is known about the life-style of mobile elements mediating horizontal gene transfer, whereas this is the ultimate determinant for their transfer fitness. Here, we investigate the life-style of an integrative and conjugative element (ICE) within the genus Pseudomonas that is a model for a widespread family transmitting genes for xenobiotic compound metabolism and antibiotic resistances. Previous work showed bimodal ICE activation, but by using single cell time-lapse microscopy coupled to combinations of chromosomally integrated single copy ICE promoter-driven fluorescence reporters, RNA sequencing and mutant analysis, we now describe the complete regulon leading to the arisal of differentiated dedicated transfer competent cells. The regulon encompasses at least three regulatory nodes and five (possibly six) further conserved gene clusters on the ICE that all become expressed under stationary phase conditions. Time-lapse microscopy indicated expression of two regulatory nodes (i.e., bisR and alpA-bisDC) to precede that of the other clusters. Notably, expression of all clusters except of bisR was confined to the same cell subpopulation, and was dependent on the same key ICE regulatory factors. The ICE thus only transfers from a small fraction of cells in a population, with an estimated proportion of between 1.7–4%, which express various components of a dedicated transfer competence program imposed by the ICE, and form the centerpiece of ICE conjugation. The components mediating transfer competence are widely conserved, underscoring their selected fitness for efficient transfer of this class of mobile elements.

STrack: A Tool to Simply Track Bacterial Cells in Microscopy Time-Lapse Images

“…Cell tracking in time-lapse images is important because it allows to gain insight in the real-time behavior of bacteria, on how cells divide, move, or express specific other characteristics (e.g., activation of mobile elements [ 19 ] and induction of tailocins [ 18 ]). Identifying segmented cells and arranging them into lineages by hand or semi manually quickly becomes untractable.…”

STrack: A tool to Simply Track bacterial cells in microscopy time-lapse images

“…Cell tracking in time-lapse images is important because it allows to gain insight in the real-time behaviour of bacteria, on how cells divide, move, or express specific other characteristics (e.g., activation of mobile elements (Sulser et al, [2022]), induction of tailocyns (Vacheron et al STrack was meant to track segmented objects in time-lapses. The quality of segmentation thus plays a crucial role, as mis-segmentations such as missed cells or merged cells will inevitably have a deleterious impact on the tool that tries to link these cells between frames.…”

“…Cell tracking in time-lapse images is important because it allows to gain insight in the real-time behaviour of bacteria, on how cells divide, move, or express specific other characteristics (e.g., activation of mobile elements (Sulser et al, [2022]), induction of tailocyns (Vacheron et al [2021])). Identifying segmented cells and arranging them into lineages by hand or semi manually quickly becomes untractable.…”

Key Role of Transconjugants for Dissemination of the Integrative Conjugative Element ICE Bs1 in Biofilms

“…Work done on ICEclc regulation nicely illustrates how ICE regulation can be complex, with three regulatory nodes and at least five gene clusters constituting the full ICE regulon (11,12). A "bistability" generator orchestrates the choice between the two routes of ICE life cycle (remaining silent or being activated).…”