Chitons modulate pH to biomineralize magnetite

Chitons have multi-toothed, rasp-like feeding organs called radulas. They coat the largest teeth in their radula with magnetite. We discovered they do so, in part, by modulating pH  to favor magnetite production. In the animated 3D reconstruction above, we see a region of a radula from Acanthopleura granulata in which low pH areas appear blue (due to applying the pH-sensitive dye Ageladine-A and imaging with a confocal microscope). The grey space is tissue and the negative spaces are the locations of teeth. As seen here, channels of low pH (< 4) run underneath the teeth and there are areas of low pH near the edges of developing teeth. Image by Rebecca Varney (UCSB).

The radula of the chiton A. granulata. New teeth are made continuously at the posterior end of the radula (left) and they move forward as they are mineralized with apatite, then with an intermediate layer of ferrihydrite, and finally with a thick cap of magnetite. Chitons use the teeth at the anterior of  the radula (right) for feeding until they wear out and are replaced with new teeth. The blue box indicates the site of the animated 3D reconstruction shown above. In this area, chitons begin adding thick caps of magnetite to their teeth, a process made possible by precise spatial and temporal control of pH in the radula. Scale bar = 3mm. Image by Rebecca Varney (UCSB).