Insights into the Geomicrobiology of Biovermiculations from Rock Billet Incubation Experiments

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.

Diversity of Iron Oxides: Mechanisms of Formation, Physical Properties and Applications

“…Compositions with mixed iron oxides can originate via a biogenic route, including microbial direct or non-direct biomineralization [388][389][390], anoxygenic photosynthesis by a photoferrotrophic bacterium [391] and the reduction of solid ferric hydroxide by iron-reducing bacteria [392]. Biogenic iron oxide structures can be used in microbial iron reduction studies [392], banded iron formations [391] or hydrothermal vent field studies [389] and waste remediation [390].…”

“…Finally, in some cases, such structures are used for various environmental tasks, including environmental safety [396], environmental remediation [397], boreal forest studies [398], inositol phosphate selective retention in soil [399], biovermiculation studies [388] and the Earth and planetary deep interior studies [24].…”