Severin Schink, Mark Polk, Edward Athaide, Avik Mukherjee, Constantin Ammar, Xili Liu, Seungeun Oh, Yu-Fang Chang, and Markus Basan. 11/22/2021. “
The energy requirements of ion homeostasis determine the lifespan of starving bacteria.” bioRxiv, Pp. 11/22/2021. 11.22.469587.
Publisher's VersionAbstractThe majority of microbes on earth, whether they live in the ocean, the soil or in animals, are not growing, but instead struggling to survive starvation
1–6. Some genes and environmental conditions affecting starvation survival have been identified
7–13, but despite almost a century of study
14–16, we do not know which processes lead to irreversible loss of viability, which maintenance processes counteract them and how lifespan is determined from the balance of these opposing processes. Here, we used time-lapse microscopy to capture and characterize the cell death process of
E. coli during carbon starvation for the first time. We found that a lack of nutrients results in the collapse of ion homeostasis, triggering a positive-feedback cascade of osmotic swelling and membrane permeabilization that ultimately results in lysis. Based on these findings, we hypothesized that ion transport is the major energetic requirement for starving cells and the primary determinant of the timing of lysis. We therefore developed a mathematical model that integrates ion homeostasis and ‘cannibalistic’ nutrient recycling from perished cells
16,17 to predict lifespan changes under diverse conditions, such as changes of cell size, medium composition, and prior growth conditions. Guided by model predictions, we found that cell death during starvation could be dramatically slowed by replacing inorganic ions from the medium with a non-permeating osmoprotectant, removing the cost of ion homeostasis and preventing lysis. Our quantitative and predictive model explains how survival kinetics are determined in starvation and elucidates the mechanistic underpinnings of starvation survival.
schinketal2021.pdf Seungeun Oh, Changhee Lee, Wenlong Yang, Ang Li, Avik Mukherjee, Markus Basan, Chongzhao Ran, Wei Yin, Clifford J. Tabin, Dan Fu, X. Sunney Xie, and Marc W. Kirschner. 9/15/2021. “
Protein and Lipid Mass Concentration Measurement in Tissues by Stimulated Raman Scattering Microscopy.” PNAS, 119, 17, Pp. e2117938119.
Publisher's VersionAbstractCell mass and chemical composition are important aggregate cellular properties that are especially relevant to physiological processes, such as growth control and tissue homeostasis. Despite their importance, it has been difficult to measure these features quantitatively at the individual cell level in intact tissue. Here, we introduce normalized Raman imaging (NoRI), a stimulated Raman scattering (SRS) microscopy method that provides the local concentrations of protein, lipid, and water from live or fixed tissue samples with high spatial resolution. Using NoRI, we demonstrate that protein, lipid, and water concentrations at the single cell are maintained in a tight range in cells under the same physiological conditions and are altered in different physiological states, such as cell cycle stages, attachment to substrates of different stiffness, or by entering senescence. In animal tissues, protein and lipid concentration varies with cell types, yet an unexpected cell-to-cell heterogeneity was found in cerebellar Purkinje cells. The protein and lipid concentration profile provides means to quantitatively compare disease-related pathology, as demonstrated using models of Alzheimer’s disease. This demonstration shows that NoRI is a broadly applicable technique for probing the biological regulation of protein mass, lipid mass, and water mass for studies of cellular and tissue growth, homeostasis, and disease.
nori.pdf