What is the benefit of forming bundles? We don't fully understand this yet. Maybe it protects fibers from phage, degradation, or shearing? Or, it could promote biofilm formation, similar to what is seen in archaic chaperone-usher pathway pili. Or, it might enable electron transfer between cells.

This electroactive bacterium has a long doubling time (~1 d). It probably allocates a lot energy expenditure to make those nanowire bundles. Interestingly, hemes within a single fiber are well insulated, and the heme-heme distance between fibers seems too far to allow electrons to jump between them.

Finally, this pilus was reported to be conductive many years ago. However, our structure shows no molecular basis for this, and our bulk measurements confirm the pili are not conductive. It's not surprising—why would a photosynthetic bacterium need to adopt the anaerobic respiration lifestyle?

Intriguingly, we also showed this pilus can bind microcystin on its surface! 😜 This binding may be achieved by a unique glycosylation pattern, allowing the bacteria to enrich these toxins, which could potentially aid in their survival.

These pili are crucial for the bacteria to maintain its water column position. Since we lack genetic knockout tools, we temporarily sheared the pili off. Without them, the bacteria could no longer remain where they were. The cells remained viable, and the pili were regenerated after a few hours.