Proc. Natl. Acad. Sci. USA, published online 20 Aug 2012; doi:10.1073/pnas.1209742109

Credit: NATACHA RUIZ

Bacteria regulate their cell size, growth rate and division depending on the availability of nutrients, growing larger and faster in nutrient-rich medium, but there is limited mechanistic information as to how E. coli regulate cell size in response to nutrients. Yao et al. shed new light on this process by examining mutations in the fatty acid (FA) biosynthetic gene fabH, found in a screen for suppressors of mutations in transport of lipopolysaccharide (LPS) from the inner membrane to the cell surface. Deletion of fabH allows survival of cells with very limited LPS at the cell surface, and FabH is essential in mutants where synthesis of the small regulatory molecule ppGpp is compromised. fabH mutants have a small-colony phenotype and altered FA composition that the authors detected by gas chromatography. Mutants also have a marked reduction in cell surface area (50%) and in cell volume (70%) in rich medium. Inhibition of FA biosynthesis by two additional independent strategies suggests that the slow-growth and small-size phenotypes are not related to changes in FA composition but rather are due to changes in FA biosynthesis capacity. Finally, fabH mutants have a 75% reduced rate of cell envelope elongation. These results suggest that FA biosynthesis regulates cell size in response to nutrients by regulating cell envelope growth and that deletion of fabH restores balance between LPS assembly rates and envelope biogenesis.