Conjugative Transfer from Escherichia coli to Gram-positive Bacteria: A Systematic Review and Meta-Analysis

Conjugative DNA transfer is a major driver of microbial evolution and an essential tool for biotechnological applications. While conjugation between Gram-negative and Gram-positive bacteria has been observed, its efficiency and underlying principles remain poorly understood. This systematic review and meta-analysis assess the success and influencing factors of Escherichia coli-to-Gram-positive conjugation. A systematic search of the PubMed, Crossref and Web of Science database (up to July 2025) identified 41 studies reporting E. coli-to-Gram-positive conjugation, comprising 645 measurements. Studies were included based on experimental evidence of conjugative transfer and reported efficiency values. Data extraction was performed manually, and statistical analyses were conducted to identify key trends. We found that E. coli-to-Gram-positive conjugation is significantly less efficient than E. coli-to-E. coli or E. coli-to-other Gram-negative bacteria. However, certain recipient strains and optimized conditions enable surprisingly high efficiencies, within 1-2 orders of magnitude of E. coli-to-E. coli conjugation. Strategies that improve efficiency include altering plasmid methylation patterns, optimizing cation concentrations, and modifying donor-recipient ratios. Limitations include potential bias toward well-studied bacterial groups (e.g., Streptomycetaceae), variability in experimental conditions, and incomplete reporting in some studies. Further research should explore additional recipient strains, refine conjugation mechanisms, and optimize transfer conditions to enhance DNA delivery to non-model microbes. Understanding these processes may pave the way for more efficient and universal DNA transfer methods across diverse microbial taxa. ImportanceBacteria have an incredible ability to share genetic material with each other, a process that drives evolution and enables survival in changing environments. Conjugation allows bacteria to pass DNA from one cell to another. Scientists have used this process to engineer microbes for medicine, agriculture, and environmental cleanup. However, transferring DNA between very different types of bacteria, especially from E. coli (a Gram-negative bacterium) to Gram-positive bacteria, has remained a challenge. This study reviewed over 600 experiments to understand when and how such transfers work best. Surprisingly, the researchers found that under certain conditions, DNA can move across this divide much more efficiently than previously thought. These insights could help scientists develop universal DNA delivery tools, unlocking the potential of hard-to-engineer bacteria for biotechnology. In a world that increasingly relies on microbes for sustainable solutions, improving how we "send instructions" into these microbial workers is a critical step forward.