1/n - Our paper is out! Briefly, we show that a biosurfactant (detergent molecule) made by B. subtilis depolarizes cell membranes to protects cells from dying when I suffocate them (by depleting oxygen). See rest of thread to learn more about this story!
cell.com/current-biolog…
cell.com/current-biolog…
2/n - This is an example of where an interesting observation on the bench turned into a substantial research process - utilizing the scientific method. I noticed that my cell cultures became clearer over time on the bench. The cells were actually lysing (breaking apart).
3/n - B. subtilis (the bacterium I work with) requires oxygen to create ATP for energy and I knew that depriving these bacteria of oxygen was not good. We used an oxygen nanosensor made by Cassandra Fraser and Chris DeRosa to show growing cultures depleted oxygen in the media.
4/n - I hypothesized that oxygen limitation in standing cultures caused lysis - so I limited oxygen by completely sealing the cultures (which would allow cells to consume the oxygen that is available) would cause them to lyse (shown by the decrease in OD600 (culture cloudiness)).
5/n You might notice the different lysis upon oxygen depletion between the wild (3610) and the lab (168) strains of B. subtilis. Despite the fact that 168 lysed less (had more biomass in the culture tube), it was actually much more dead (the cells in the tube could not recover).
6/n Therefore, despite the fact that strain 168 cultures are more cloudy (and contain more cells), these cells are less viable. When I cultured the strains together, I rescued viability of strain 168, suggesting that strain 3610 is secreting a molecule keeps it viable.
7/n Long story short, the molecule is surfactin. This is a strong detergent molecule produced by wild B. subtilis (3610) and the lab strain can't make it. Adding surfactin alone restores viability to the cultures.
8/n We show that surfactin depolarizes B. subtilis and that adding a depolarizing agent will also restore viability to the lab strains in the absence of surfactin.
9/n Why would this depolarization be important to maintain viability? We have evidence suggesting the depolarization would reduce O2 consumption and may alter the redox state of the cells, allowing them to transition to a state where they can stay viable until oxygen is restored.
10/n - We also show through genetic screens that surfactin is the primary determinant of this viability loss (hat tip to my summer undergraduate Lam Vo). It remains a mystery why 90% of the cells die and lyse while 10% remain viable in the wild strain.
11/n - We show that surfactin also improves growth yield through enhancing oxygen diffusion (supported by Lisa Willis, who did the math to make sure the numbers we were getting empirically were reasonable).
12/12 - There is much more to the story, so please check out the manuscript! I'm happy to field any questions here. Also, a thanks to my PI, KC Huang who let me run with this story back when it was an interesting observation on the bench and our awesome collaborator Dan Kearns.
p.s. I just want to share a slide that I am working on for a presentation next week. "Nancy Drew and the mystery of the dying cells." Spoiler alert, I killed the bacterial cells. Case closed.
P.p.s. I forgot to state why this matters. Bacteria undergo changes in O2 levels (i.e. floods limit O2 in soil) and its impt to understand their responses to this and other stresses soil bacteria encounter. Understanding this may help us engineer more stress resistant soil bugs.
P.p.p.s. Membrane potential is impt for many aspects of cell physiology including our new finding that it protects cells from O2 deprivation. It will be interesting to see if depolarizing the membrane helps protect cells from other stresses.
