Compartmentalization and spatiotemporal organization of macromolecules in bacteria

Abstract

For many years, the bacterial cells were regarded as tiny vessels lacking internal organization. This view, which stemmed from the scarcity of membrane‐bounded organelles, has changed considerably in recent years, mainly due to advancements in imaging capabilities. Consequently, despite the rareness of conventional organelles, bacteria are now known to have an intricate internal organization, which is vital for many cellular processes. The list of bacterial macromolecules reported to have distinct localization patterns is rapidly growing. Moreover, time‐lapse imaging revealed the spatiotemporal dynamics of various bacterial macromolecules. Although the regulatory mechanisms that underlie macromolecules localization in bacterial cells are largely unknown, certain strategies elucidated thus far include the establishment of cell polarity, the employment of cytoskeletal proteins, and the use of the membrane properties, that is, curvature, electric potential, and composition, as localization signals. The most surprising mechanism discovered thus far is targeting of certain mRNAs to the subcellular domains where their protein products are required. This mechanism relies on localization features in the mRNA itself and does not depend on translation. Localization of other mRNAs near their genetic loci suggests that the bacterial chromosome is involved in organizing gene expression. Taken together, the deep‐rooted separation between cells with nucleus and without is currently changing, highlighting bacteria as suitable models for studying universal mechanisms underlying cell architecture.

Chromosome-Membrane Interactions in Bacteria

“…In recent decades, it has become well established that some lipids and proteins are not homogeneously distributed in the membrane. This heterogeneity may lead to microdomains, or areas of specific lipid-lipid or lipid-protein interaction (reviewed in 24,29). In addition, recent data support the view that membrane proteins can control the formation of domains with specific lipid compositions (73).…”

The membrane: transertion as an organizing principle in membrane heterogeneity

“…A heterogeneous distribution of proteins in the cell envelope of bacteria, despite their size, has been widely demonstrated (see reviews, Shapiro et al, 2002; Fishov and Norris, 2012b; Govindarajan et al, 2012). During the course of investigation of specific biological functions and processes, this heterogeneity has been revealed mainly by visualization with GFP-fusions and immunofluorescence to take the form of polar, patchy and helix-like distributions in the membranes.…”

“…It comprises proteins, EI and HPr, which are common to all substrates, as well as sugar-specific permeases, enzymes II (EIIs). Interestingly, EI and HPr are mainly located near the poles of E. coli cell (Patel et al, 2004; Lopian et al, 2010; Govindarajan et al, 2012). Upon addition of the sugar to the growth medium, HPr is phosphorylated by EI; HPr-P produced is released from the polar membranes and distributes in the cell, though EI remains located near the poles of negatively curved sites (Govindarajan et al, 2013; see Membrane Curvature and Protein Location).…”

Comparative Subcellular Localization Analysis of Magnetosome Proteins Reveals a Unique Localization Behavior of Mms6 Protein onto Magnetite Crystals

“…Whereas some of these compartments are completely proteinaceous (e.g., carboxysomes, metabolosomes, and ferritin) (1-3), others contain molecular components similar to those in cell membranes, including lipids and proteins (e.g., nucleoids, polyhydroxybutyrate, and spores) (4,5). Such compartmentalized organelles are recognized to be formed within bacteria through multiple processes involving the spatial regulation of protein localization, but the details of this regulatory machinery remain largely unknown (6).…”