Fig 1.
Arthrospira platensis strain C005.
(A) The morphology of helical and (B) straight trichomes of Arthrospira platensis used in the experiment. Scale bars represent a length of 300 μm.
Fig 2.
The mechanical properties of Arthrospira trichomes.
(A) The persistence length (Lp) of straight (Median ± SD = [2 ± 3] x 103 μm) and helical trichomes (Median ± SD = [37 ± 58] x 103 μm) measured along the center of the trichomes represented by white dash lines (left panel). Helical trichomes have a statistically significant greater Lp than straight trichomes (t-test, p < 0.001). The values shown in (A) are raw data from 3 replicates and represented by boxplots. The circles in the boxplots represent the medians from each replicate. (B) Elastic moduli (E) calculated from the middle of straight (Median ± SD = 2.3 ± 0.5 MPa) and helical trichomes (Median ± SD = 2.4 ± 0.5 MPa) have no significant difference (t-test, p = 0.722, α = 0.01). Raw data is represented by boxplots with the same manner as in (A). All statistical testing in this section was performed with the MATLAB Statistical Package.
Fig 3.
(A) The 3D geometric models of a straight trichome with Rhelix = 0 μm, and helical trichomes with Rhelix = 7.5 and 15 μm were constructed as thin rods (upper panel). The cross-sections from the middle of trichomes (L = 150 μm) moves away from the centroid as Rhelix increases (lower panel). (B) The estimated flexural rigidity (kf) increases as Rhelix increases. The gray stripe indicates the possible range of kf calculated from the measured E.
Fig 4.
Patterns of gliding trajectories of helical and straight trichomes.
Examples of the trajectories here were constructed from the position of the gliding trichomes on the solid media’s surface within the static field of view collected every 5 minutes. The starting point of the trajectories presented in these figures is set at the origin, (0, 0), for the purpose of visualization. (A) Gliding patterns of the straight trichomes are more directional. The trajectories tend to point away from the starting point in particular directions. Some trichomes were found to switch directions. Snap turns were also observed occasionally. (B) On the other hand, gliding patterns of the helical trichomes are less directional. The trajectories involve frequent random turns and twists.
Fig 5.
Straight Arthrospira trichomes (left panel) exhibited better gliding motility and were able to move for a longer distance, while helical trichomes (right panel) remained near the initial positions. The image sequences of both strains were taken at t = 0, 7, 14 and 21 min respectively. The arrows represent the positions of trichomes (see S1 Movie.).
Fig 6.
Speed and directionality ratio of the gliding motility of straight and helical trichomes (A) The scatter and box plots represent the raw data and distribution for the trichomes’ gliding speed (v) respectively. Based on data collected from 32 straight and 51 helical trichomes, the average v of straight and helical trichomes (median ± SD) are 0.13 ± 0.10 μm/sec and 0.02 ± 0.02 μm/sec respectively. The gliding speeds of the two morphologies are significantly different (t-test, p < 0.001). (B) The scatter and box plots represent the raw data and distribution for the trichomes’ gliding directionality ratio (d/D) respectively. Based on data collected from 32 straight and 51 helical trichomes, the average d/D of straight and helical trichomes (median ± SD) are 0.45 ± 0.32 and 0.19 ± 0.16 respectively. The gliding directionality ratios of the two morphologies are significantly different (t-test, p < 0.001). There is no significant correlation between d/D and duration of gliding in both straight and helical trichomes (Pearson Product Moment Correlation, p = 0.149 and 0.153, respectively, α = 0.05).