UC Berkeley

Though small in size, there is a growing appreciation for the complex ultrastructure of bacteria and archaea. This complexity and beauty is exemplified by the diverse protein- and lipid-bounded organelles that have been discovered. The first chapter of this dissertation, a published review article, introduces different lipid-bounded organelles that have been found in bacteria and archaea. The best-studied lipid-bounded organelles in bacteria are the magnetosomes of magnetotactic bacteria. This chapter discusses, in depth, the mechanism of magnetosome formation in two Magnetospirillum spp. that make cubooctahedral-shaped magnetite crystals within the magnetosome lumen. This chapter also discusses what is known about other, more mysterious, organelles, including bullet- shaped magnetosomes, anammoxosomes, and nucleus-like organelles in archaea.

Tools for genome editing are a major limiting factor when attempting to elucidate the structure and function of organelles. As such, there are few model systems for studying organelle formation. The second chapter of this dissertation, a published primary research article, describes a method for genome editing in Desulfovibrio magneticus RS-1. This work is the first example of gene editing for an anaerobic bacterium that makes bullet- shaped magnetosomes and marks a major step in magnetosome research.

In addition to making magnetosomes, D. magneticus makes ferrosomes, which are membrane-bounded organelles that contain iron, oxygen, and phosphorus. Ferrosomes were discovered serendipitously when former Komeili lab postdoctoral scholar, Dr. Meghan Byrne, observed that D. magneticus cells transitioning out of iron starvation are full of electron-dense granules, now named ferrosomes. The third chapter of this dissertation uncovers the genetic basis of ferrosomes. Using the genetic method we developed for D. magneticus, we show that ferrosomes require a set of genes that encode proteins associated with isolated ferrosomes. In addition to D. magneticus, diverse bacteria, and perhaps archaea, require a similar set of genes to make ferrosomes. Finally, we show that ferrosomes likely have an important role in iron homeostasis during anaerobic metabolism. Future research on bullet-shaped magnetosomes and ferrosome formation, function, and regulation are introduced in the final chapter of this dissertation.