Glycine Betaine synthesis and transport Proteins, BetTIBA and ProPU, in Escherichia coli K12 do not confer Resistance to SDS-EDTA induced Outer Membrane Stress

Abstract

Glycine betaine is a small organic molecule derived from choline that acts as an osmoprotectant in Escherichia coli responsible for providing cellular stability during environmental stress. It is synthesized by biosynthetic proteins encoded in the betTIBA operon and transported in and out of the cell by the ProP and ProU transporters. Among its various functions, it is also known to protect the cell against abiotic stress factors by acting as a chemical chaperone to prevent protein denaturation. Knowing that glycine betaine can perform a myriad of functions, we were interested in determining whether this osmolyte confers resistance to outer membrane stress in E. coli. Here, we attempted to determine if E. coli that is unable to synthesize glycine betaine, due to a betTIBA deletion and/or proPU deletion, would affect cell susceptibility to SDS-EDTA induced outer membrane stress by assessing cell viability. Cell viability was measured by determining growth of the wild-type, ΔbetTIBA, and ΔbetTIBAΔproPU mutants over a 16-hour period through OD₆₀₀ readings using the EpochTM Microplate Spectrophotometer (Biotek). Results from growth assays under SDS-EDTA conditions showed that betTIBA and proPU deletions resulted in decreased susceptibility to SDS-EDTA relative to the no SDS control. The results suggest that glycine betaine does not contribute to protecting the outer membrane from stress factors such as SDS and EDTA.