17 Live cell time-lapse microscopy, a widely-used technique to study gene expression and protein 18 dynamics in single cells, relies on segmentation and tracking of individual cells for data 19 generation. The potential of the data that can be extracted from this technique is limited by the 20 inability to accurately segment a large number of cells from such microscopy images and track 21 them over long periods of time. Existing segmentation and tracking algorithms either require 22 additional dyes or markers specific to segmentation or they are highly specific to one imaging 23 condition and cell morphology and/or necessitate manual correction. Here we introduce a fully 24 automated, fast and robust segmentation and tracking algorithm for budding yeast that 25 overcomes these limitations. Full automatization is achieved through a novel automated seeding 26 method, which first generates coarse seeds, then automatically fine-tunes cell boundaries using 27 these seeds and automatically corrects segmentation mistakes. Our algorithm can accurately 28 segment and track individual yeast cells without any specific dye or biomarker. Moreover, we 29 show how existing channels devoted to a biological process of interest can be used to improve 30 the segmentation. The algorithm is versatile in that it accurately segments not only cycling cells 31 with smooth elliptical shapes, but also cells with arbitrary morphologies (e.g. sporulating and 32 pheromone treated cells). In addition, the algorithm is largely independent of the specific 33 imaging method (bright-field/phase) and objective used (40X/63X). We validate our algorithm's 34 performance on 9 cases each entailing a different imaging condition, objective magnification 35 and/or cell morphology. Taken together, our algorithm presents a powerful segmentation and 36 tracking tool that can be adapted to numerous budding yeast single-cell studies.3 37 Introduction 38 Traditional life science methods that rely on the synchronization and homogenization of cell 39 populations have been used with great success to address numerous questions; however, they 40 mask dynamic cellular events such as oscillations, all-or-none switches, and bistable states [1][2][3][4][5].41 To capture and study such behaviors, the process of interest should be followed over time at 42 single cell resolution [6][7][8]. A widely used method to achieve this spatial and temporal resolution 43 is live-cell time-lapse microscopy [9], which has two general requirements for extracting single-44 cell data: First, single-cell boundaries have to be identified for each time-point (segmentation), 45 and second, cells have to be tracked over time (tracking) [10, 11]. 46 47 One of the widely-used model organisms in live-cell microscopy is budding yeast Sacchromyces 48 cerevisiae, which is easy to handle, has tractable genetics, and a short generation time [12, 13].49 Most importantly in the context of image analysis, budding yeast cells have smooth cell 50 boundaries and are mostly stationary while growing, which ca...