Biomedical subjects

Andrew E Pelling

Publications and source records attributed to Andrew E Pelling.

5 recordsLinked to original sources

PubMed2006

Self-organized and highly ordered domain structures within swarms of Myxococcus xanthus.

Coordinated group movement (swarming) is a key aspect of Myxococcus xanthus' social behavior. Here we report observation of domain structures formed by multiple cells within large three-dimensional swarming groups grown on amorphous glass substrates, using the atomic force microscope (AFM). Novel analyses revealed that 90% of the wild type swarms displayed some form of preferential cell alignment. In contrast, cells with mutations in the social and adventurous motility systems displayed a distinct lack of cell alignment. Video microscopy observations of domain features of in vivo swarming M. xanthus cells were also consistent with the AFM data. The results presented here reveal that unique domain formation within swarms of wild type cells is a biologically driven process requiring the social and adventurous motility systems and is not a statistical phenomenon or thermodynamic process arising from liquid crystal behavior.

Microscopy, Atomic Force↗

PubMed2005

Nanoscale visualization and characterization of Myxococcus xanthus cells with atomic force microscopy.

Multicellular microbial communities are the predominant form of existence for microorganisms in nature. As one of the most primitive social organisms, Myxococcus xanthus has been an ideal model bacterium for studying intercellular interaction and multicellular organization. Through previous genetic and EM studies, various extracellular appendages and matrix components have been found to be involved in the social behavior of M. xanthus, but none of them was directly visualized and analyzed under native conditions. Here, we used atomic force microscopy (AFM) imaging and in vivo force spectroscopy to characterize these cellular structures under native conditions. AFM imaging revealed morphological details on the extracellular ultrastructures at an unprecedented resolution, and in vivo force spectroscopy of live cells in fluid allowed us to nanomechanically characterize extracellular polymeric substances. The findings provide the basis for AFM as a useful tool for investigating microbial-surface ultrastructures and nanomechanical properties under native conditions.

Bacterial Adhesion↗

PubMed2005

Analysis of type IV pilus and its associated motility in Myxococcus xanthus using an antibody reactive with native pilin and pili.

Myxococcus xanthus possesses a social gliding motility that requires type IV pili (TFP). According to the current model, M. xanthus pili attach to an external substrate and retract, pulling the cell body forward along their long axis. By analogy with the situation in other bacteria employing TFP-dependent motility, M. xanthus pili have been assumed to be composed of pilin (PilA) subunits, but this has not previously been confirmed. The first 28 amino acids of the M. xanthus PilA protein share extensive homology with the N-terminal oligomerization domain of pilins in other bacterial species. To facilitate purification, the authors engineered a truncated form of M. xanthus PilA lacking the first 28 amino acids and purified this protein in soluble form. Polyclonal antibody generated against this protein was reactive with native pilin and pili. Using this antibody, it was confirmed that TFP of M. xanthus are indeed composed of PilA, and that TFP are located unipolarly and required for social gliding motility via retraction. Using tethering as well as motility assays, details of pili function in M. xanthus social motility were further examined.

Amino Acid Sequence↗

PubMed2004

DNA base pair resolution by single molecule force spectroscopy.

The forces that hold complementary strands of DNA together in a double helix, and the role of base mismatches in these, are examined by single molecule force spectroscopy using an atomic force microscope (AFM). These forces are important when considering the binding of proteins to DNA, since these proteins often mechanically stretch the DNA during their action. In AFM measurement of forces, there is an inherent instrumental limitation that makes it difficult to compare results from different experimental runs. This is circumvented by using an oligonucleotide microarray, which allowed a direct comparison of the forces between perfectly matched short oligonucleotides and those containing a single or double mismatch. Through this greatly increased sensitivity, the force contribution of a single AT base pair was derived. The results indicate that the contribution to forces from the stacking interactions is more important than that from hydrogen bonding.

Base Pair Mismatch↗

PubMed2004

Local nanomechanical motion of the cell wall of Saccharomyces cerevisiae.

We demonstrate that the cell wall of living Saccharomyces cerevisiae (baker's yeast) exhibits local temperature-dependent nanomechanical motion at characteristic frequencies. The periodic motions in the range of 0.8 to 1.6 kHz with amplitudes of approximately 3 nm were measured using the cantilever of an atomic force microscope (AFM). Exposure of the cells to a metabolic inhibitor causes the periodic motion to cease. From the strong frequency dependence on temperature, we derive an activation energy of 58 kJ/mol, which is consistent with the cell's metabolism involving molecular motors such as kinesin, dynein, and myosin. The magnitude of the forces observed ( approximately 10 nN) suggests concerted nanomechanical activity is operative in the cell.

Biomechanical Phenomena↗