Geological Society of America

T191 Harnessing “Omics” to Advance the Geosciences: New Paradigms and Platforms for Observing Earth Systems

Tuesday, 21 October 2014
8:00 AM - 12:00 PM
304/305

METAGENOMIC INSIGHTS INTO CONE FORMATION IN HOT SPRING MICROBIAL MATS

Paper number: T191-2
Program: Technical Sessions
Time: 8:03 AM – 8:18 AM

Authors

Lewis M. Ward Presenting Author
California Institute of Technology, Pasadena, CA
Frank Corsetti
University of Southern California, Los Angeles, CA
Zak Kerrigan
University of Rhode Island, Narragansett, RI
Heda Agić
Uppsala University, Uppsala, N/A
Marisol Juarez Rivera
University of California-Davis, Davis, CA
Victoria A. Petryshyn
University of California, Los Angeles, Los Angeles, CA
Blake W. Stamps
University of Oklahoma, Norman, OK
Hope A. Johnson
California State University, Fullerton, Fullerton, CA
Bradley S. Stevenson
University of Oklahoma, Norman, OK
John Spear
Colorado School of Mines, Golden, CO

Abstract

Conical stromatolites (Conophyton) are among the best records of microbial life in deep time, as unlike other stromatolites they are not known to form abiogenically. Cones can be found in modern microbial mats, potentially serving as analogs of conical stromatolites. Mechanisms of cone formation are not well understood, though several hypotheses have been proposed including phototaxis and bubble formation. In association with the 2014 International Geobiology Course, we have collected field observations and conducted metagenomic analyses of a modern cone-forming microbial mat from a hot spring in California (Little Hot Creek) to investigate potential mechanisms underlying their formation.

Initial observations of cones in Little Hot Creek revealed surface-normal growth on slopes and under overhangs rather than vertically, suggesting that neither phototaxis nor bubble production are driving cone formation. Bubble production was only observed in flat regions of the mat and not in cones, indicating that there is not a strong association between bubbles and cones. This was further supported by the absence of known phototaxis-associated genes in metagenomic data from both the cones and the surrounding flat mat. Comparison of the metagenomes from the cones and the surrounding mat revealed shared predominant taxa and functional genes between both sample types, differing only in relative abundance and the presence of some low-abundance sequences. Both samples were primarily composed of the phyla Cyanobacteria and Chloroflexi, with the coccoidal cyanobacterium genus Synechococcus and the filamentous, photoheterotrophic chloroflexi genus Roseiflexus as dominant members of both samples. The filamentous cyanobacterium genus Phormidium was highly enriched in the cone samples, suggesting a potential role for abundant filaments in cone formation.

Our study suggests that cone formation can be independent of bubble formation or phototaxis. Alternative mechanisms could be involved, such as differential gene expression, diffusion limitation of nutrients, or the stochastic aggregation of filamentous microbes. These mechanisms could potentially be driven by processes other than oxygenic photosynthesis, and therefore might have implications for interpretation of cones in the rock record.