Cell Division Resets Polarity and Motility for the Bacterium Myxococcus xanthus

Abstract

e Links between cell division and other cellular processes are poorly understood. It is difficult to simultaneously examine division and function in most cell types. Most of the research probing aspects of cell division has experimented with stationary or immobilized cells or distinctly asymmetrical cells. Here we took an alternative approach by examining cell division events within motile groups of cells growing on solid medium by time-lapse microscopy. A total of 558 cell divisions were identified among approximately 12,000 cells. We found an interconnection of division, motility, and polarity in the bacterium Myxococcus xanthus. For every division event, motile cells stop moving to divide. Progeny cells of binary fission subsequently move in opposing directions. This behavior involves M. xanthus Frz proteins that regulate M. xanthus motility reversals but is independent of type IV pilus "S motility." The inheritance of opposing polarity is correlated with the distribution of the G protein RomR within these dividing cells. The constriction at the point of division limits the intracellular distribution of RomR. Thus, the asymmetric distribution of RomR at the parent cell poles becomes mirrored at new poles initiated at the site of division. Many approaches to study cell division utilize traits that readily allow the distinction of two progeny cells. For example, cells displaying "asymmetrical" division traits allow the clear distinction of numerous characteristics that can then be monitored while deciphering other unknowns. Caulobacter bacteria are among the best studied with this distinction (1), but other biological examples include: preneuron neuroblast brain cells, budding Saccharomyces cerevisiae, germ line cells of male Drosophila, endospore development by Bacillus species, and Mycobacterium species subjected to environmental nutrient stress (2, 3). While such explicitly distinct examples may be rare, nearly all types of cells display some asymmetrical properties when functioning properly. There are numerous examples of distinctive asymmetrical and polarized attributes of cells (4). However, one difficulty that remains in characterizing asymmetrical properties in biology is distinguishing the timing and order of those intra-and intercellular attributes that are transient in nature. Alternative to studying asymmetric cell types that can be readily differentiated, other research strategies to probe stages of division often examine stationary or immobilized cells.Myxococcus xanthus is one of many myxobacteria, common soil microbes that grow readily in environments rich in complex organics, such as those containing decaying plants (5) or other bacteria (6). M. xanthus cells exhibit a symmetric morphology. The specific mechanism and dynamics of M. xanthus cell division, like those of most nonmodel organisms, are not entirely known. M. xanthus is among many bacteria lacking a clear MinCD system that drives the recruitment of FtsZ for division. It is known that the middle of M. xanthus cells is marked by PomZ, w...

Evolutionary diversification of the RomR protein of the invasive deltaproteobacterium, Bdellovibrio bacteriovorus

“…However, whether RomR Bd as a growth-controller is a scaffold protein that recruits other proteins to the poles, or has a direct role in growth, is currently unknown. Harvey and coworkers 33 established that RomR Mx is recruited to the site of M. xanthus cell division to reset polarity for the daughter cells. This allows asymmetric localisation, important for motility in the parent cell, to be emulated in the daughter cells 33 .…”

“…Harvey and coworkers 33 established that RomR Mx is recruited to the site of M. xanthus cell division to reset polarity for the daughter cells. This allows asymmetric localisation, important for motility in the parent cell, to be emulated in the daughter cells 33 . They suggested that RomR Mx may interact with proteins of the developing cell poles; it is therefore conceivable that RomR Bd works together with polar growth components in B. bacteriovorus , having evolved a key role in establishing polarity during cell division 33 .…”

Real-time Image Denoising of Mixed Poisson-Gaussian Noise in Fluorescence Microscopy Images using ImageJ

“…This sample and imaging method was chosen to produce experimental results with low average contrast (0.52), far outside of the training distribution. Sample preparation and microscope configuration is described in [45, 46]: unlabeled bacteria are illuminated with 458 nm laser to excite flavins in the bacteria, resulting in autofluorescence. The microscope is configured as an widefield epi-fluorescence microscopy using a single dichroic mirror as both excitation and emission filter, resulting in the excitation light leakage and/or back scattering being detected by the imaging EM-CCD.…”

The bacterial division protein MinDE has an independent function in flagellation

“…Simultaneous examination of bacterial division and motility is extremely challenging; thus the relationship between cell division and cell motility is poorly understood. A recent study showed that Myxococcus xanthus stops its motility during its division and resumes only after completion of the division ( 38 ). Similarly, during the exponential growth of E. coli , the flagellar gene expression is repressed and bacterial adhesion is enhanced ( 39 ).…”