The Role of Extracellular Polymeric Substances in the Silicification of Calothrix: Evidence from Microbial Mat Communities in Hot Springs at Yellowstone National Park, USA

Abstract

We provide nanoscale evidence of the role of sheath exopolymers in the silicification of the sheathed cyanobacteria Calothrix. Electron microscope observations of silicified Calothrix cells revealed that silica accretes directly onto EPS sheath fibrils to produce an open web of silica particles that could remain permeable to nutrients and waste products. We also found that silicified Calothrix cells from different microhabitats contained morphologically distinct silica particles. Differences in silicification texture suggest that environmental variables may influence silicification at the nanoscale. We develop a framework based on aggregation kinetics to address silicification processes in Calothrix and other sheathed cyanobacteria.

Keywords:

• silification
• Calothrix
• TEM
• EPS
• biosignatures

Acknowledgments

This article is based upon work supported by NASA under award No NNG04GJ84G to SLC. Specimens were collected from Yellowstone National Park under Permit # YELL-01994 to SLC. The authors thank the referees and appreciate the helpful discussion with Profs. Nancy Hinman and Carrine Blank at the University of Montana.