Phosphotransferase system sugars immediately induce mutations of Cra in an Escherichia coli ptsH mutant

Abstract

Most bacteria use the phosphoenolpyruvate (PEP):sugar phosphotransferase system (PTS) to catalyse coupled transport and phosphorylation of sugars. The PTS consists of several sugar‐specific components (enzyme IIs) and two general components: enzyme I, encoded by ptsI, and HPr, encoded by ptsH, which are common to most PTS carbohydrates. Although both enzyme I and HPr are believed to be required to utilize these PTS sugars, an E. coli ptsH mutant has been reported to exhibit a leaky growth phenotype on these sugars. Here, we show that this phenomenon occurs because the ptsH mutant undergoes adaptive mutations in the presence of PTS sugars within a few generation times. The ptsH mutant cells once exposed to a PTS sugar showed a growth rate similar to that of the wild‐type strain when transferred to fresh medium supplemented with the same PTS sugar, suggesting the acquisition of additional genetic variations. Genome sequencing revealed that the PTS sugar‐adapted variants harboured loss‐of‐function mutations in cra, which increased expression of the fruBKA operon. Our results suggest that the presence of a PTS sugar can exert a strong selective pressure when a general PTS component is defective.

The role of the universal sugar transport system components PtsI (EI) and PtsH (HPr) in Enterococcus faecium

“…The deletion of ptsI, ptsH , or both results in an inability to utilize sugars that are entirely dependent on PTS. Single ptsH mutants have demonstrated a leaky phenotype in other species, owing to adaptive mutations (Min and Seok 2022 ); therefore, we created a double ptsHI clean deletion mutant in E. faecium NCTC7171, NCTC7171∆ ptsHI . To validate the mutant phenotype, we grew it alongside the wild-type (WT) strain on Bile Esculin Agar.…”