We initially attempted to use the bending modulus implied from Boal and Ng’s study, however we found that during simulations this value seemed to be too low. The trichomes were completely flaccid and would collapse into a heap as soon as one collided with another trichome, unlike the smooth sinuous shape filamentous cyanobacteria often display. In the paper we justify (at some length) the bending modulus we used, which we extrapolated from various sources, and explain why we believe the value in Boal and Ng’s study is likely too low. The reviewer did not question the logic or the sources used to arrive at this value, but nevertheless seemed surprised at the result. The reviewer claims that the parameter falls outside of the physical regime, but doesn’t offer a justification other than that the implied persistence length “seems too large”. However, the large persistence length simply implies that the cyanobacteria are stiff enough that they are largely unaffected by thermal fluctuations. Despite this, the trichomes in our simulations are still quite flexible in practice, as can be seen in Figure 4. Even if the virtual trichomes are somewhat too stiff, we do not feel that this would have a major impact on the results.
The literature seems to indicate a low value of the bending modulus (alpha) that corresponds to a persistence length of 500 microns. The authors instead use alpha = 2 × 10−21 Nm2, which is 1000× larger. With this value, the persistence length = alpha/(kbT) = 0.5 metres. This seems orders of magnitude too large, especially in the face of the results of Boal and Ng [44]. The authors need to be in a physical regime of parameter space in order to confront their results with observed patterns. Otherwise, they are just fitting a non-linear phenomenon with a (potentially inappropriate) non-linear model— in this case agreement does not provide firm insight into the physical system.