HOW BACTERIA COPE WITH OSMOTIC SHOCK

Following publication in the leading Proceedings of the National Academy of Sciences, Ph.D. student Smitha Hegde summarises her team’s research on bacterial osmoregulation

Following publication in the leading Proceedings of the National Academy of Sciences, Ph.D. student Smitha Hegde summarises her team’s research on bacterial osmoregulation

Research from the lab of Dr Teuta Pilizota from the University of Edinburgh has elucidated how bacteria manage to stay in control of their pressure and cell volume when placed in environments with low osmolarity. This insight could help better understand the behaviour of microbes in industrial biotech processing or when faced with antibiotic treatment.

Bacteria live and grow under significant osmotic pressure – the difference between osmolarity inside the cell and that of the environment. To help bacteria cope with shifts in osmotic pressure they rely heavily on mechanosensitive channels. 

Single-cell, high resolution imaging is used to monitor what happens when the common gut bacteria, Escherichia coli, is subject to a sudden decrease in external osmolarity (called a ‘downshock’). Water floods into the cell, which would burst the cell if mechanosensitive channels were not forced open by the increase in tension in the membrane of the swollen cell. The channels then allow solutes and water to flow out, which stabilises the cell volume and prevents the cell from bursting. The process, while allowing control of cell volume and pressure, is passive. Once the channels open the control happens as a consequence of competition between solutes flowing inwards and water both outwards and inwards. For the first time, single-cell analysis of live cells showed that after a ‘downshock,’ a bacterial cell will first swell rapidly and then shrink back slowly to its original (and often smaller) size. This is a consequence of the passive nature of the process, it servers an emergency pressure release valve that as a consequence lacks tight control.  However, the cells could continue to grow normally apparently unaffected by the insult.

Teuta and her team built and tested a model of this sequence of events using parameters associated with the flow of solutes and water across the cell membrane through the mechanosensitive channels. The model provided an accurate prediction of cell size changes.

Understanding how these systems are regulated is key to understanding how bacteria can survive in what can be harsh and hostile environments. This project is in collaboration with biologics manufacturing company, FUJIFILM Diosynth Biotechnologies, who is interested in how microbes are influenced by the culture conditions and increased amount of protein production within industrial-sized bioreactors. Optimising the environment for industrial microbes could deliver substantial improvements in yield and productivity for many valuable products. 

The research was published in PNAS