Horizontal gene transfer (HGT) is the process by which DNA is transferred from a donor cell to a recipient that is not part of its progeny. Mechanisms of HGT in prokaryotes include transformation, transduction, and conjugation; the latter of which transfers plasmids or chromosomally excised DNA like integrative and conjugative elements (ICEs) from a donor to a recipient in a cell-to-cell dependent contact. ICEs are widespread autonomous mobile DNA, containing the genes necessary for integration, excision, and the conjugative machinery. ICEclc of Pseudomonas putida is our experimental model and is characterized by the presence of the clc genes for chlorocatechol degradation. Its transfer is initiated from a subpopulation of cells (3-5%) that become transfer competent (tc). The proportion of tc cells is the highest when cultures have been grown on 3-chlorobenzoate (3CBA) as a sole carbon source and when they enter stationary phase. However, the link between growth on 3CBA and ICEclc transfer competence activation is unknown. Our aim is to better understand the influence of environmental factors on ICEclc activation, assuming that growth on 3CBA induces metabolic pathways in Pseudomonas which relate to tc cell formation. To identify such potential pathways, we use microbial single-cell RNA sequencing (scRNAseq) and quantify differences in transcript abundances in single cells growing on different carbon sources. We were able to differentiate tc- from non-tc cells based on their transcriptional fingerprints, and further detected carbon source and growth phase signatures. Tc cell-specific expression signatures identified by scRNAseq will be followed up in genetic and reporter studies.