title: Long-term microfluidic tracking of coccoid cyanobacterial cells reveals robust control of division timing.
abstract: Cyanobacteria are important agents in global carbon and nitrogen cycling and hold great promise for biotechnological applications. Model organisms such as Synechocystis sp. and Synechococcus sp. have advanced our understanding of photosynthetic capacity and circadian behavior, mostly using population-level measurements in which the behavior of individuals cannot be monitored. Synechocystis sp. cells are small and divide slowly, requiring long-term experiments to track single cells. Thus, the cumulative effects of drift over long periods can cause difficulties in monitoring and quantifying cell growth and division dynamics.
  
  
  
  To overcome this challenge, we enhanced a microfluidic cell-culture device and developed an image analysis pipeline for robust lineage reconstruction. This allowed simultaneous tracking of many cells over multiple generations, and revealed that cells expand exponentially throughout their cell cycle. Generation times were highly correlated for sister cells, but not between mother and daughter cells. Relationships between birth size, division size, and generation time indicated that cell-size control was inconsistent with the "sizer" rule, where division timing is based on cell size, or the "timer" rule, where division occurs after a fixed time interval. Instead, single cell growth statistics were most consistent with the "adder" rule, in which division occurs after a constant increment in cell volume. Cells exposed to light-dark cycles exhibited growth and division only during the light period; dark phases pause but do not disrupt cell-cycle control.
  
  
  
  Our analyses revealed that the "adder" model can explain both the growth-related statistics of single Synechocystis cells and the correlation between sister cell generation times. We also observed rapid phenotypic response to light-dark transitions at the single cell level, highlighting the critical role of light in cyanobacterial cell-cycle control. Our findings suggest that by monitoring the growth kinetics of individual cells we can build testable models of circadian control of the cell cycle in cyanobacteria.
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA, 94305, USA.|Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA.
authors.forename: Feiqiao Brian
authors.initials: FB
authors.lastname: Yu
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA.|Sainsbury Laboratory, Cambridge University, Cambridge, CB2 1LR, UK.
authors.forename: Lisa
authors.initials: L
authors.lastname: Willis
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA.
authors.forename: Rosanna Man Wah
authors.initials: RM
authors.lastname: Chau
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA.|Department of Industrial Engineering, University of Padova, Padova, 35131, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Zambon
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA, 94305, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Horowitz
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, 94305, USA. dbhaya@stanford.edu.
authors.forename: Devaki
authors.initials: D
authors.lastname: Bhaya
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA. kchuang@stanford.edu.|Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA, 94305, USA. kchuang@stanford.edu.
authors.forename: Kerwyn Casey
authors.initials: KC
authors.lastname: Huang
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA. quake@stanford.edu.|Chan Zuckerberg Biohub, San Francisco, CA, 94158, USA. quake@stanford.edu.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Quake
mesh_terms: D002455:Cell Division / Q000528:radiation effects; D049109:Cell Proliferation; D058948:Cell Tracking / Q000379:methods*; D007091:Image Processing, Computer-Assisted; D008027:Light; D044085:Microfluidics / Q000379:methods*; D008954:Models, Biological; D011336:Probability; D046939:Synechocystis / Q000166:cytology* / Q000254:growth & development / Q000528:radiation effects; D013997:Time Factors
keywords: Cell-size homeostasis; Circadian clock; Cyanobacteria; Light-dark cycles; Microfluidics; Photosynthesis; Single-cell imaging