Date of Award

Spring 2011

Document Type

Restricted Thesis

Terms of Use

© 2011 Amy E. Langdon. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

Amy Cheng Vollmer


This study was a morphological, metabolic and phylogenetic comparison of species of the Sphaerotilus-Leptothrix iron bacteria. This is the first such study to include genes from the type species Leptothrix ochracea and two new isolates of the Leptothrix genus found in a freshwater stream in Boothbay Harbor, ME. It is also the first documentation that L. cholodnii and both isolates exhibit false branching, holdfasts, and autotrophy. The multi-locus sequence analysis (MLSA) included the sequences of both the small and large ribosomal subunits and of the gyrB or parE genes from Sphaerotilus, the three cultured Leptothrix species and the two isolates. This revealed that Leptothrix ochracea is only distantly related to the subsequently named Leptothrix species, consistently showing less sequence identity to the other Leptothrix species than either Sphaerotilus natans or Methylibium petroleiphilum. This will result in the division of the Sphaerotilus-Leptothrix group into three genera and the renaming of all other Leptothrix species. After further characterization, the isolates MK9 and LD2C will be added to the third genus of filamentous iron bacteria as new species.