Insights into the Geomicrobiology of Biovermiculations from Rock Billet Incubation Experiments.

Daniel S. Jones,Penelope J. Boston,Hilary Kelly,Michael N. Spilde

doi:10.3390/life11010059

Abstract

Biovermiculations are uniquely patterned organic rich sediment formations found on the walls of caves and other subterranean environments. These distinctive worm-like features are the combined result of physical and biological processes. The diverse microbial communities that inhabit biovermiculations may corrode the host rock, form secondary minerals, and produce biofilms that stabilize the sediment matrix, thus altering cave surfaces and contributing to the formation of these wall deposits. In this study, we incubated basalt, limestone, and monzonite rock billets in biovermiculation mixed natural community enrichments for 468–604 days, and used scanning electron microscopy (SEM) to assess surface textures and biofilms that developed over the course of the experiment. We observed alteration of rock billet surfaces associated with biofilms and microbial filaments, particularly etch pits and other corrosion features in olivine and other silicates, calcite dissolution textures, and the formation of secondary minerals including phosphates, clays, and iron oxides. We identified twelve distinct biofilm morphotypes that varied based on rock type and the drying method used in sample preparation. These corrosion features and microbial structures inform potential biological mechanisms for the alteration of cave walls, and provide insight into possible small-scale macroscopically visible biosignatures that could augment the utility of biovermiculations and similarly patterned deposits for astrobiology and life detection applications.

Highlights

Biovermiculations are geometrically distinct microbial mat communities that occur on cave surfaces [1,2,3,4,5,6]
7. (A) Apatite crystal covered in phosphatic can residue basalt sample incubated in Mn carbonateenlargement medium andby
Biovermiculations aresoaked widely soaked in phosphate buffer

Summary

Introduction

Biovermiculations are geometrically distinct microbial mat communities that occur on cave surfaces [1,2,3,4,5,6] These formations exhibit a network of “worm-like” tracks and splotches that are typically in positive relief compared to the surrounding substrate (Figure 1). We use the term “biovermiculation” here in sensu Hose et al [8], who found substantial microbial biomass and biofilm in biovermiculations from sulfide-rich Villa Luz cave. This term is used more broadly, based on the recognition of a substantial microbial content in vermiculations in many cave systems (e.g., [6,7,9]). Similar formations have been observed at the sub-millimeter scale in cyanobacterial hypoliths on the underside of a translucent rock in Strzelecki Desert, Australia [10] as well as in higher vegetation patterns in the Negev Desert, Israel that exhibit biovermiculation geometry on a multi-meter scale [11]

Methods

Results

Conclusion