Geomicrobiology of Cave Ferromanganese Deposits: A Field and Laboratory Investigation

Abstract

Unusual ferromanganese deposits are found in several caves in New Mexico. The deposits are enriched in iron and manganese by as much as three orders of magnitude over the bedrock, differing significantly in mineralogy and chemistry from bedrock-derived insoluble residue. The deposits contain metabolically active microbial communities. Enrichment cultures inoculated from the ferromanganese deposits produced manganese oxides that were initially amorphous but developed into crystalline minerals over an 8-month period and beyond; no such progression occurred in killed controls. Phylogenetic analyses of sequences from clone libraries constructed from culture DNA identified two genera known to oxidize manganese, but most clones represent previously unknown manganese oxidizers. We suggest that this community is breaking down the bedrock and accumulating iron and manganese oxides in an oligotrophic environment.

Keywords:

• biomineral
• birnessite
• caves
• ferromanganese deposits
• Lechuguilla Cave
• manganese-oxidizing bacteria
• microbially influenced corrosion

Acknowledgments

This research was funded by grants from the National Science Foundation, Life in Extreme Environments Program (DEB9809096 to C. Dahm) and Biogeosciences Program (EAR0311932 to D. Northup and EAR0311930 to P. Boston). We acknowledge technical support from the University of New Mexico's Molecular Biology Facility which is supported by NIH Grant Number 1P20RR18754 from the Institute Development Award (IDeA) Program of the National Center for Research Resources. We thank the National Park Service for permission to collect at Lechuguilla and Spider Caves, and we especially thank Dale Pate, Stan Allison and Paul Burger at Carlsbad Caverns National Park for their help and support. Larry Mallory contributed greatly to the design and debugging of the AO/INT procedure, and John Craig and John Husler often contributed their efforts to make analytical equipment and procedures work properly. We thank Jim Werker and Val Hildreth-Werker for help with field logistics in Lechuguilla Cave, Sue Barns and Tina Vesbach for assistance with the phylogenetic tree, and David Estes for sequence editing. Gratitude is expressed to Brad Tebo and three anonymous reviewers for constructive comments and criticism.

Notes

^a Rock flour milled from rock at sampling sites.

^b Gerhardt (1994).

^c Atlas and Parks (1993).

^a Number of samples in parentheses.

^b WC-1 IR, Insoluble residue remaining after acid dissolution of backreef dolostone sample WC-1; all other results are averages.

^c Weight loss on drying, chemical analysis reported on dry weight basis.

^d Total Fe reported as Fe₂O₃

^e Approximate abundance given by number of asterisk, from as most abundant to as trace; gypsum observed as trace in punk rock, lepidocrocite trace in chocolate brown/black FMD.