Robustness to Sub-optimal Temperatures of the Processes of Tsr Cluster Formation and Positioning in Escherichia Coli

Abstract

Clustering and positioning of chemotaxis-associated proteins are believed to be essential steps for their proper functioning. We investigate the robustness of these processes to sub-optimal temperatures by studying the size and location of clusters of Tsr-Venus proteins in live cells. We find that the degree of clustering of Tsr proteins is maximal under optimal temperature. The data further suggests that the weakening of the clustering process in lower-than and higher-than optimal temperatures is not due to the same cause. Meanwhile, the location of the clusters is found to be weakly temperature independent, within the range tested. We conclude that while the clustering of Tsr is heavily temperature dependent, the localization is only weakly dependent, suggesting that the functionality of the proteins responsible for retaining Tsr-clusters at the cell poles, such as the Tol-Pal complex, is robust to suboptimal temperatures.

Polar Localization of the Serine Chemoreceptor of Escherichia coli Is Nucleoid Exclusion-Dependent

“…Recent studies showed that the nucleoid plays a central role in the spatial organization of plasmids (31,32) and unwanted protein aggregates (33,34) in the cytoplasm of E. coli, as well as in the choice of location of the cell-division septum (61). By showing how the nucleoid contributes to the spatial organization of sensory complexes, and thus to the functional response of E. coli populations to various external stresses (43,62,63), our study further supports the notion that the nucleoid is critical for generating heterogeneities and asymmetries in the cytoplasm of E. coli that are essential for intracellular spatial organization and, combined with cell division, for cell-to-cell diversity within lineages.…”

“…The image analysis procedure included cell segmentation, lineage construction, detection and characterization of fluorescent spots (Tsr clusters) and nucleoids, and characterization of the spatial distributions of clusters and nucleoids. The various steps were performed using custom-made software that integrates components from the software MAMLE (41) and CellAging (42), along with the cluster-detection method proposed in (43).…”

“…Lineage construction, when needed, was automatically performed by CellAging (42) and then manually corrected. Detection and characterization of the size and intensity of fluorescent Tsr clusters were performed as described in (43), by defining a cluster as a connected component, with each pixel having a light intensity above a threshold. For this purpose, we assume that the background pixel intensities follow a Gaussian distribution with the same median and upper quartile as the pixels in the cell.…”