Structural basis of H-NS-mediated temperature-dependent stimulation of initial growth in Escherichia coli

Bacteria rapidly initiate growth when entering warm-blooded hosts to ensure reproductive success. We investigated the temperature-dependent stimulation of the specific growth rate at the onset of the logarithmic phase (defined as μ at ODratio = 0.2) in Escherichia coli. High-frequency automated monitoring revealed that this stimulation peaks near 37°C and is strain-specific. Comparative analysis between MG1655 and W3110 type A identified the Rac prophage as a primary genomic determinant for this acceleration. However, growth stimulation is uniquely dependent on H-NS, which we redefine as a nucleoid structural organizer. Genetic complementation and comparative analysis of nucleoid-associated proteins (NAPs), and single-cell nucleoid imaging confirmed that H-NS provides a mandatory physical scaffold specifically at host temperatures. We propose that H-NS undergoes a conformational switch to a parallel dimer form around 37°C, enabling the nucleoid to adopt the highly condensed state required for managing replication-transcription conflicts during rapid growth bursts. Notably, while MG1655 relies primarily on H-NS for this stimulation, W3110 type A requires a distributed network of NAPs, including HU and StpA, to maintain its growth velocity. This effect is environment-specific, becoming particularly significant under minimal media conditions where metabolic and structural coordination requirements are more stringent, but less pronounced in nutrient-rich conditions. These findings resolve the silencing paradox: hns-deficient mutants grow slowly at 37°C because they lack the structural infrastructure required to physically coordinate the rapid onset of growth, regardless of the de-repression of growth-promoting genes. We conclude that H-NS-mediated physical organization of the genome is a fundamental prerequisite for temperature-dependent growth adaptation and successful host colonization.