Accumulation of 3-(N-morpholino)propanesulfonate by osmotically stressed Escherichia coli K-12
Related Experiment Videos
S Cayley1, M T Record, B A Lewis
1Department of Chemistry, University of Wisconsin, Madison 53706.
Abstract:
We found that exogenous morpholinopropanesulfonate (MOPS) is concentrated approximately fivefold in the free volume of the cytoplasm of Escherichia coli K-12 (strain MG1665) when grown at high osmolarity (1.1 OsM) in two different media containing 40 mM MOPS. MOPS was not accumulated by E. coli grown in low-osmolarity MOPS-buffered medium or in 1.1 OsM MOPS-buffered medium containing the osmoprotectant glycine betaine. Salmonella typhimurium LT2 did not accumulate MOPS under any condition examined. We infer that accumulation of MOPS by E. coli K-12 is not due to passive equilibration but rather to transport, possibly involving an as yet uncharacterized porter not present in S. typhimurium. Glutamate and MOPS were the only anionic osmolytes we observed by 13C nuclear magnetic resonance in E. coli K-12 grown in MOPS-buffered medium. The increase in positive charge accompanying the increase in the steady-state amount of K+ in cells shifted from low to high external osmolarity appeared to be compensated for by changes in the amounts of putrescine, glutamate, and MOPS. MOPS is not an osmoprotectant, because its accumulation did not increase cell growth rate.
Insights
Escherichia coli K-12 accumulates morpholinopropanesulfonate (MOPS) at high osmolarity, indicating active transport. This accumulation does not enhance bacterial growth, suggesting MOPS is not an osmoprotectant.
Area of Science:
- Microbiology
- Bacterial Physiology
- Molecular Transport
Background:
- Bacterial cells regulate internal osmolarity to survive environmental changes.
- Morpholinopropanesulfonate (MOPS) is a zwitterionic buffering agent.
- Osmoprotectants are compounds that help cells withstand osmotic stress.
Purpose of the Study:
- To investigate the accumulation of morpholinopropanesulfonate (MOPS) in Escherichia coli K-12.
- To determine if MOPS accumulation is related to osmotic stress response.
- To identify the mechanism of MOPS uptake and its role in bacterial physiology.
Main Methods:
- Culturing Escherichia coli K-12 and Salmonella typhimurium LT2 under varying osmolarity conditions.
- Using 13C nuclear magnetic resonance (NMR) to observe intracellular osmolytes.
- Measuring the intracellular concentration of MOPS and other ions (K+, putrescine, glutamate).
Main Results:
- Escherichia coli K-12 accumulated exogenous morpholinopropanesulfonate (MOPS) approximately fivefold in the cytoplasm at high osmolarity (1.1 OsM).
- MOPS accumulation was not observed in low-osmolarity conditions or when glycine betaine was present.
- Salmonella typhimurium LT2 did not accumulate MOPS under any tested conditions, suggesting a species-specific transport mechanism.
- MOPS accumulation did not increase the growth rate of E. coli, indicating it is not an osmoprotectant.
- Intracellular K+, putrescine, glutamate, and MOPS levels changed to compensate for osmotic shifts.
Conclusions:
- MOPS accumulation in E. coli K-12 is likely mediated by a specific transport system, not passive diffusion.
- A distinct, uncharacterized transporter may be responsible for MOPS uptake in E. coli, absent in Salmonella.
- MOPS functions as an anionic osmolyte but does not confer osmoprotection to E. coli.