Arthrospira platensis, commonly known as spirulina, can take on discrete morphologies depending on environmental conditions: helical as the name implies but also linear! theyre shapechanging out here

Aureispira is a predatory bacterium which uses a heptameric "grappling hook" to catch prey and reel itself in then shotgun blast them to death with a type 6 secretion system

Actinosynnema can grow insane branching fractal mycelial hyphae-like synemata structures in agar medium and into the air. they found that guy in New Jersey!

ok those are 3 interesting bacteria whose names start with 'A' that I can think of rn