BPS2026 – How do bacteria adapt their size to high pressure environments?

Recently, it has been shown that upwards of 80%–90% of all microbes can be found in high pressure environments. While the processes governing cell division and cell size regulation of microbes is relatively well understood at atmospheric pressure, how microbes adapt their growth and division to modulate cell size and shape in high pressure environments remains unknown. Protein complexes, such as the ribosome, which is crucial for growth, and the division ring GTPase, FtsZ, which is essential for cytokinesis, are sensitive to pressure. Any pressure-induced change in the balance between growth and division will impact cell size. To better study how pressure adaptation affects cell size, we investigated the pressure dependence of size in a strain of E. coli (AN62) evolved in the laboratory to grow at pressures up to 62 MPa. When grown at atmospheric pressure, strain AN62 cells were half the size of those of its ancestor, E. coli strain MG1655, despite the limited number of mutations (only 17) in strain AN62 compared to strain MG1655. Moreover, none of the mutations are in genes involved in cell division or morphology regulation. In this work, we performed an in-depth analysis of the cause of the small cell size phenotype in strain AN62 and determined its relevance to its ability to grow under pressure. Specifically, we determined that the mutations to glutamine synthetase ( glnA ) and the transcriptional regulator of the cysteine operon ( cysB ) are necessary and sufficient to cause the small cell size phenotype of AN62. Additionally, we examined how pressure affects cell size in strain AN62 and analyzed it through the context of growth rate, divisome availability/functionality, and the amount of chromosome replication.