Chemical changes in mutant E. coli exhibiting impaired plasmid transfer have been identified both on, and within the bacterial envelope using time-of-flight secondary ion mass spectrometry (ToF-SIMS).
E. coli strains carrying mutations in the cellular envelope affecting their ability to transfer plasmids, a large contributor to the spread of antibiotic resistance, have been analysed using ToF-SIMS , a surface sensitive analytical technique in which chemicals are ejected from a sample surface using an ion beam and their mass calculated based on how long it takes for them to travel a certain distance and reach a detector.
The ability to monitor the specific chemical structure of the cellular envelope is of great importance since the envelope provides bacteria structure and the means for interaction with the extra cellular environment. Using ToF-SIMS we were able to both analyse the exposed surface and also use the ion beam to gradually remove the outer membrane and enter the periplasm. Thereby we were able to profile some of the building blocks from the very surface through the outer membrane into the periplasm.
In this study, we could see a difference in both amount and composition of lipids, components that make up a large portion of the cellular envelope. We also saw that one of the mutations appeared to be missing cyclic enterobacterial common antigen (ECACYC), thought to be involved in permeability regulation of the E. coli cellular envelope.
The paper can be found here: https://pubs.acs.org/doi/abs/10.1021/acs.analchem.9b02533