There might be a misunderstanding in the first part. The rotation of filament does not drive macroscopic rotation or spiral formation. What we describe in the text was the switch to turn to the left was governed by the filament rotation, but the real formation of a spiral is driven by the locomotion of the filament. The cited paper described the clumping of Anabaena cylindria in a dense culture. The clumping or aggregation in Arthrospira (Ohmori group) is mediated by cAMP, but A. cylindrica might be different. I have been using Anabaena for about 40 years, but I have never seen Anabaena filaments form a spiral on agar plates. Spiral formation and clumping are different phenomena. It is difficult to discuss the relationship (if any) between clumping and rotation.
The authors’ conclusions are generally well supported and the electron microscopy provides some of the clearest images to date of the junctional pores.