We study many different topics, but here are some of our recurring efforts and papers (see publications for a full list)

Rod shape formation and growth

We started by working to understand how bacteria form into rods and grow in rod shapes. The proteins that cause bacteria to have rod shape are collectively called the “Rod complex,” a series of extracellular facing enzymes linked to cytoplasmic filaments of MreB and actin homolog.  This complex rotates around the width of a bacteria, a motion powered by the enzymes building new cell wall. (Carl Wivagg and Saman Hussain)

In the below papers, we detail how 1. the Rod complex moves around the width of bacteria (rather than along its length), and 2) how rod shape is formed by this complex: As the MreB filaments point around the rod, the activity of the associated cell wall synthesis enzymes is constrained so that it builds hoops around the rod (like hoops on a barrel). These hoops contain the bacteria along the width, causing it to only grow along its length. (Mike Dion, Mrinal Kapoor, Yingie Sun, F. Wong) 

• Hussain S, Wivagg CN, Szwedziak P, Wong F, Schaefer K, Izoré T, Renner LD, Holmes MJ, Sun Y, Bisson-Filho AW, Walker S, Amir A, Lowe J, Garner EC*. MreB filaments align along greatest principal membrane curvature to orient cell wall synthesis. Elife. 2018 Feb 22;7:123
• Wong F, Garner EC*, Amir A*. Mechanics and dynamics of translocating MreB filaments on curved membranes. Elife. 2019 Feb 18;8. 
• Dion M, Kapoor M, Sun Y, Wilson S, Ryan J, Vigouroux A, van Teeffelen S, Oldenbourg R, Garner EC. Cell Diameter in Bacillus subtilis is Determined by the Opposing Actions of Two Distinct Cell Wall Synthetic Systems. Nat Microbiol. Nature Publishing Group; 2019 May 13;24:1. doi: 10.1038/s41564-019-0439-0. Epub 2019 May 13. PMID: 31086310; PMCID: PMC6656618.
• Garner EC, Bernard R, Wang W, Zhuang X*, Rudner DZ*, Mitchison T*. Coupled, circumferential motions of the cell wall synthesis machinery and MreB filaments in B. subtilis. 2011 Jul 8;333(6039):222-5. doi: 10.1126/science.1203285. Epub 2011 Jun 2. PMID: 21636745; PMCID: PMC3235694.

A general review of rod shape formation.

• Garner EC. Toward a Mechanistic Understanding of Bacterial Rod Shape Formation and Regulation. Annu Rev Cell Dev Biol. 2021 Oct 6;37:1-21. doi: 10.1146/annurev-cellbio-010521-010834. Epub 2021 Jun 29. PMID: 34186006.

We are next moving into understanding the role of cell wall hydrolases in the growth and architecture of the cell wall and how they are regulated by forces and chemical environments.  We also are examining how the cell regulates the number of MreB filaments and active enzymes at the biochemical and kinetic level. 

Regulation of bacterial growth by cell wall precursors.

We have recently begun to explore how the bacteria co-regulate the rate of different biosynthetic processes in the cell. Here we explored how the cell controls the rate of cell wall synthesis relative to growth rate.  Surprisingly, we found that the overall cellular growth rate was relegated by the cell wall precursor lipid II, signaling that is mediated by the kinase PrkC. This work showed Monod’s growth law does not hold for Bacillus (they have spare ribosomal capacity), and we can make them grow faster than they should in carbon-limited media (Yingjie Sun and Syliva Hurlmann) 

• Sun Y†, Hürlimann S†, Garner E. Growth rate is modulated by monitoring cell wall precursors in Bacillus subtilis. Nat Microbiol. 2023 Mar;8(3):469-480. doi: 10.1038/s41564-023-01329-7. Epub 2023 Feb 16. PMID: 36797487.

The forces and mechanisms underlying bacterial cell division.

Our recent studies also brought us into the field of bacterial cell division, where we examined the dynamics of the proteins of the “divisome”, the macihery that divides the cell, which contains the polyemrs FtsZ and FtsA, as well as division enzymes and other proteins.   

Our first study of the B. subtilis division machinery discovered that FtsZ/FtsA filaments treadmill around the division plane, and that – in rich growth – the rate the enzymes move around the cell, the rate they insert material into the cell wall is limited by the treadmilling rate, and that the rate the Z ring constricts to divide bacteria is limited by the treadmilling rate (Alex Bisson, Georga Squyres).

• Bisson-Filho AW†, Hsu Y-P†, Squyres GR†, Kuru E†, Wu F, Jukes C, Sun Y, Dekker C*, Holden S*, VanNieuwenhze MS*, Brun YV*, Garner EC*. Treadmilling by FtsZ filaments drives peptidoglycan synthesis and bacterial cell division. Science. 2017 Feb 17;355(6326):739-43. doi: 10.1126/science.aak9973. Erratum in: Science. 2020 Jan 17;367(6475): PMID: 28209898; PMCID: PMC5485650.

We next examined the role of the proteins that bind to FtsZ. While the FtsZ binding proteins have no effects on the treadmilling rates or filament lengths in vivo, their essential role is to condense FtsZ filaments into a sharp ring: without condensation, the rings remain as loose spirals, and even though the associated enzymes still make cell wall, the cells cannot initiate cell division without ring condensation, and the cells eventually die (Georgia Squyres and Matt Holmes). 

• Squyres GR, Holmes MJ, Barger SR, Pennycook BR, Ryan J, Yan VT, Garner EC. Single-molecule imaging reveals that Z-ring condensation is essential for cell division in Bacillus subtilis. Nat Microbiol. 2021 May;6(5):553-562. doi: 10.1038/s41564-021-00878-z. Epub 2021 Mar 18. PMID: 33737746; PMCID: PMC8085161.

We are currently underway elucidating the physical mechanisms by which the cell division machinery can exert force the membrane inward (against turgor pressure) so the cell can initiate division. 

Growth and cytoskeletal filaments within archaea 

Working with Amy Schmid at UNC, we started working with the high-salt archaea, Halobacterium salanarium, as it is an easily optically tractable archaea for cell biology. 

Our first work with the Amir group examined the growth of this bug and found that, just like bacteria, it grows via an adder model-type mechanism (Jenna Eun).

• Zheng J, Mallon J, Lammers A, Rados T, Litschel T, Moody ERR, Ramirez-Diaz DA, Schmid A, Williams TA, Bisson-Filho AW*, Garner E*. Salactin, a dynamically unstable actin homolog in Haloarchaea. mBio. 2023 Nov 15:e0227223. doi: 10.1128/mbio.02272-23. PMID: 37966230.

We next found an actin-like protein in Halobacterium salanarium that grows out of the poles toward the middle of the cell and then suddenly shrinks. This is the first archaeal actin homolog thought to exhibit dynamic instability and appears to be involved in segregating the chromosomes of this archaea when phosphate is limiting. (Jenny Zheng, Alexande Bisson)

• Eun Y-J, Ho P-Y, Kim M, LaRussa S, Robert L, Renner LD, Schmid A*, Garner E*, Amir A*. Archaeal cells share common size control with bacteria despite noisier growth and division. Nat Microbiol. 2018 Feb;3(2):148-154. DOI: 10.1038/s41564-017-0082-6. PMID: 29255255.

General review

• Bisson-Filho AW, Zheng J, Garner EC*. Archaeal imaging: leading the hunt for new discoveries.  Molecular Biology of the Cell. 2018 Jul 15;29(14):1675-81. doi: 10.1091/mboc.E17-10-060 10.1091/mbc.E17-10-0603. PMID: 30001185; PMCID: PMC6080714.

Glukokinases that regulate their activity by polymerization. 

Hexokinses are distant relatives of actin. Working with the Murray lab, we found that Glk1, a hexokinase in saccharomyces perceives, forms polymers when there is an excess of its substrates, glucose, and ATP. This acts as a throttle on Glk1’s activity, so cells do not deplete all their cellular phosphate when exposed to excess glucose after starvation conditions. Doing phylogenetic work with Tom Williams revealed that Glk’s ability to polymerize arose separately from the other actin-like proteins, indicating polymerization has evolved at least twice in the actin family. 

• Stoddard, P. R., Lynch, E. M., Farrell, D. P., Dosey, A. M., DiMaio, F., Williams, T. A., Kollman, J. M., Murray, A. W*. & Garner, EC*. Polymerization in the actin ATPase clan regulates hexokinase activity in yeast. Science. 2020 Feb 28;367(6481):1039-1042. doi: 10.1126/science.aay5359 PMID: 32108112; PMCID: PMC7846450.