# Cell density and single-cell heterogeneity reveal distinct competence induction dynamics in the high-GC Gram-positive Micrococcus luteus

## TL;DR

This study explores how Micrococcus luteus, a high-GC Gram-positive bacterium, regulates its ability to take up DNA, revealing unique dynamics influenced by cell density and single-cell heterogeneity.

## Contribution

The paper introduces a novel understanding of competence regulation in Actinomycetota, highlighting probabilistic and heterogeneous induction mechanisms.

## Key findings

- Peak transformation in M. luteus occurs during exponential growth at moderate cell densities.
- Transcription of late competence genes does not always correlate with transformability, suggesting post-transcriptional regulation.
- Single-cell analyses show gradual and heterogeneous promoter activity, lacking bistability seen in other bacteria.

## Abstract

Competence for natural transformation enables bacteria to acquire extracellular DNA and incorporate it into their genome, driving genetic diversification, DNA repair, and adaptation. While the regulatory mechanisms of competence development are well characterized in model organisms such as Bacillus subtilis and Streptococcus pneumoniae, little is known about how this process is controlled in Actinomycetota. Here, we investigate competence development in Micrococcus luteus, a high-GC Gram-positive species historically recognized for natural transformation.

Using transformation frequency assays, transcriptional reporters, single-cell flow cytometry, and fluorescence microscopy, we show that in this actinobacterial model competence is consistent with a probabilistic regulatory strategy that integrates cell density, nutrient-limitation-responsive signals, and physiological state. Peak transformation occurs during exponential growth in minimal medium at moderate inoculation densities, whereas both low and high starting densities suppress competence. Although transcription of the late competence genes comEA/EC is induced under competence-promoting conditions, this activation does not always correlate with transformability, indicating additional post-transcriptional or physiological regulation. Single-cell analyses revealed that promoter activity develops gradually and heterogeneously across the population, lacking the bistability or strong population-level coordination observed in other well-studied Gram-positive model systems.

These data characterize competence induction dynamics in M. luteus and expand our understanding of the diversity of competence regulation across bacteria. While these observations constrain plausible regulatory models—supporting density- and nutrient-sensitive, probabilistic induction with heterogeneous single-cell activation—the upstream signal(s) or regulatory cascade controlling competence in M. luteus remain to be identified. Together, the results suggest that high-GC Gram-positive Actinomycetota may employ distinct, potentially bet-hedging-like strategies to balance growth, stress responses, and horizontal gene transfer.

The online version contains supplementary material available at 10.1186/s12866-026-04757-7.