Variation in the Morphology of Bacillus mycoides Due to Applied Force and Substrate Structure

Abstract

Response to mechanical force is a well characterised phenomenon in eukaryotic organisms, helping to organise multicellular structures. Mechanotactic responses have only rarely been observed in prokaryotic taxa. This work reports on a morphological change due to variations in applied force and surface structure by Bacillus mycoides Flügge. B. mycoides is a ubiquitous soil organism well known among microbiologists for its characteristic spreading colony morphology. An apparent mechanotactic response is elicited by physical deformation of the gel media on which B.mycoides is growing, including applied forces of compression or tension. Variations in the surface such as curvature produced by casting the agar gel in the presence of curved objects also elicited the change. The morphological change in B.mycoides colonies associated with the application of force manifests as a pattern of parallel rhizoid filaments perpendicular to compressing force and parallel to stretching force in the agar medium. The phenomenon is most clearly demonstrated by reversible changes in the orientation of B. mycoides filaments during time-lapse microscopy.

Switching of the rotational direction of rhizoidal colonies in a newly isolated <i>Bacillus mycoides</i> strain Ko01

“…Since surface structure also had an impact on the Ko01 colony shapes, it is possible that the spreading of Ko01 is sensitive to the compressive and/or extensive forces on the agar surfaces. It is known that some bacteria orient themselves in response to the applied forces (elasticotaxis or mechanotaxis) (Stanier, 1942;Stratford et al, 2013). In a study with mechanotaxis B. mycoides Flugge strain, curved surfaces had a similar influence on colony shapes as we have observed in strain Ko01 (Stratford et al, 2013), suggesting that strain Ko01 is also mechanotaxis.…”

“…The chemical composition of the agar (e.g. salt concentration) or the physical forces applied to the media can affect the colony morphology (Stratford et al, 2013;Uomi et al, 2012).…”

Induced sensitivity of Bacillus subtilis colony morphology to mechanical media compression

“…We noted that the chains of B. subtilis PY79 appeared shorter than that of B. mycoides , with the former reaching a maximum of approximately 300 µm (Fig. 1C), while the can extend for millimeters(Stratford et al, 2013).…”

“…(Stanier, 1942; Fontes & Kaiser, 1999; Nan et al, 2014) Recently, the soil bacterium Bacillus mycoides was also shown to be sensitive to media perturbations. (Stratford, Woodley & Park, 2013) Interestingly, this compression response seems to occur by two different mechanisms: whereas individual Myxococcus xanthus dynamically reorients individual cells along lines of compression,(Dworkin, 1983) Bacillus mycoides instead gradually reorients the tips of chained cells as it grows. (Stratford et al, 2013)…”

“…(Dworkin, 1983) It has also been proposed as a potential tool for engineering applications in sensing environmental forces or generating patterns for nanofabrication. (Stratford et al, 2013)…”