An intracellular actin motor in bacteria?

Abstract

Actin performs structural as well as motor-like functions in eukaryotic cells. Orthologues of actin have also been identified in bacteria, where they perform an essential function during cell growth. Bacterial actins are implicated in the maintenance of rod-shaped cell morphology, and appear to form a cytoskeletal structure, localising as helical filaments underneath the cell membrane. Recently, a plasmid-borne actin orthologue has been shown to perform a mitotic-like function during segregation of a plasmid, and chromosomally encoded actin proteins were found to play an important role in chromosome segregation. Based on the findings that actin filaments are dynamic structures in two bacterial species, we propose that actins perform motor functions rather than a purely structural role in bacteria. We suggest that an intracellular motor exists in bacteria that could be derived from an ancestral actin motor that was present in cells early in evolution.

Bacterial translation elongation factor EF-Tu interacts and colocalizes with actin-like MreB protein

“…These experiments show that a decrease in the concentration of EF-Tu leads to a defect in cell morphology and in MreB localization, while translation is not detectably affected. In addition, MreB filaments did not show the dynamic turnover that characterizes MreB filaments in wild-type cells (13,14). We have shown that the dynamics of MreB filaments are essential for the proper function of the cytoskeletal element, indicating the need to ensure sufficient filament turnover (18).…”

“…These foci became most clearly visible during late exponential growth (OD 1.5-4) (Fig. 2C), and their pattern was somewhat reminiscent of the MreB cytoskeleton (12,14). Threedimensional deconvolution of Z stacks taken from cells bearing EF-Tu-CFP revealed an obvious punctuate or band-like distribution of EF-Tu ( Fig.…”

“…MreB localizes as helical filaments underneath the cell membrane, and is essential for viability, in many bacteria analyzed so far (12). In Bacillus subtilis and in Caulobacter crescentus, MreB filaments remodel within a time scale of few minutes and appear to extend at the plus end and to retract at the minus end along a helical path (13)(14)(15). Depletion of MreB results in the loss of rod shape in many bacteria, showing that it is a genuine cytoskeletal element.…”

A Novel System of Cytoskeletal Elements in the Human Pathogen Helicobacter pylori

“…A disputed question is the effect MreB exerts on the segregation of duplicated chromosomes. Interfering with MreB levels or polymerization activity has been shown to strongly impair chromosome segregation in several organisms [10],[17], but arguments against a direct involvement of MreB in segregation have also been put forward [18].…”

Bacterial Filament Systems: Toward Understanding Their Emergent Behavior and Cellular Functions

“…With the discovery that bacteria contain structural homologs of eukaryotic actin and tubulin (1,2), it was proposed that these polymers might have organizational and structural roles similar to their eukaryotic counterparts (3,4).…”