arXiv subjects

Magnus Andersson

Publications and source records attributed to Magnus Andersson.

22 records · Page 2Linked to original sources

arXiv2014

Damping effect of helix-like pili

Biopolymers are vital structures for many living organisms; for a variety of bacteria, adhesion polymers play a crucial role for the initiation of colonization. Some bacteria express, on their surface, attachment organelles (pili) that comprise subunits formed into stiff helix-like structures that possess unique biomechanical properties. These helix-like structures possess a high degree of flexibility that gives the biopolymers a unique extendibility. This has been considered beneficial for piliated bacteria adhering to host surfaces in the presence of a fluid flow. We show in this work that helix-like pili have the ability to act as efficient dampers of force that can, for a limited time, lower the load on the force-mediating adhesin-receptor bond on the tip of an individual pilus. The model presented is applied to bacteria adhering with a single pilus of either of the two most common types expressed by uropathogenic Escherichia coli, P or type 1 pili, subjected to realistic flows. The results indicate that for moderate flows (~25 mm/s) the force experienced by the adhesin-receptor interaction at the tip of the pilus can be reduced by a factor of ~6 and ~4, respectively. The uncoiling ability provides a bacterium with a "go with the flow" possibility that acts as a damping. It is surmised that this can be an important factor for the initial part of the adhesion process, in particular in turbulent flows, and thereby be of use for bacteria in their striving to survive a natural defense such as fluid rinsing actions.

physics.bio-ph↗

arXiv2014

Multibody simulation of adhesion pili

We present a coarse grained rigid multibody model of a subunit assembled helix-like polymer, e.g., adhesion pili expressed by bacteria, that is capable of describing the polymers force-extension response. With building blocks representing individual subunits the model appropriately describes the complex behavior of pili expressed by the gram-negative uropathogenic Escherichia coli bacteria under the action of an external force. Numerical simulations show that the dynamics of the model, which include both the effects of unwinding and rewinding, are in good quantitative agreement with the characteristic force-extension response as observed experimentally for type 1 and P pili. By tuning the model, it is also possible to reproduce the force-extension response in the presence of anti-shaft antibodies, which dramatically changes the mechanical properties. Thus, the model and the results in this work give enhanced understanding of how a pilus unwinds under action of external forces and provide new perspective of the complex bacterial adhesion processes.

physics.bio-ph↗

arXiv2014

Dynamic properties of bacterial pili measured by optical tweezers

The ability of uropathogenic Escherichia coli (UPEC) to cause urinary tract infections is dependent on their ability to colonize the uroepithelium. Infecting bacteria ascend the urethra to the bladder and then kidneys by attaching to the uroepithelial cells via the differential expression of adhesins. P pili are associated with pyelonephritis, the more severe infection of the kidneys. In order to find means to treat pyelonephritis, it is therefore of interest to investigate the properties P pili. The mechanical behavior of individual P pili of uropathogenic Escherichia coli has recently been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of ~1000 PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. We have earlier studied P pili regarding its stretching/elongation properties where we have found and characterized three different elongation regions, of which one constitute an unfolding of the quaternary (helical) structure of the PapA rod. It was shown that this unfolding takes place at an elongation independent force of 27 pN. We have also recently performed studies on its folding properties and shown that the unfolding/folding of the PapA rod is completely reversible. Here we present a study of the dynamical properties of the PapA rod. We show, among other things, that the unfolding force increases and that the folding force decreases with the speed of unfolding and folding respectively. Moreover, the PapA rod can be folded-unfolded a significant number of times without loosing its characteristics, a phenomenon that is believed to be important for the bacterium to keep close contact to the host tissue and consequently helps the bacterium to colonize the host tissue.

physics.bio-ph↗

arXiv2014

Structure and function of Enterotoxigenic Escherichia coli fimbriae from differing assembly pathways

Pathogenic enterotoxigenic Escherichia coli (ETEC) are the major bacterial cause of diarrhea in young children in developing countries and in travelers, causing significant mortality in children. Adhesive fimbriae are a prime virulence factor for ETEC, initiating colonization of the small intestinal epithelium. Similar to other Gram-negative bacteria, ETEC express one or more diverse fimbriae, some assembled by the chaperone-usher pathway and others by the alternate chaperone pathway. Here we elucidate structural and biophysical aspects and adaptations of each fimbrial type to its respective host niche. CS20 fimbriae are compared to CFA/I fimbriae, which are two ETEC fimbriae assembled via different pathways, and to Pfimbriae from uropathogenic E. coli. Many fimbriae unwind from their native helical filament to an extended linear conformation under force, thereby sustaining adhesion by reducing load at the point of contact between the bacterium and the target cell. CFA/I fimbriae require the least force to unwind, followed by CS20 fimbriae and then P-fimbriae, which require the highest unwinding force. We conclude from our electron microscopy reconstructions, modeling, and force spectroscopy data that the target niche plays a central role in the biophysical properties of fimbriae that are critical for bacterial pathophysiology.

physics.bio-ph↗