2 Sedimentary Geology, Paleoclimatology, and Paleontology

Monday, 19 May 2014
8:00 AM - 12:00 PM
SUB 233/235

SUCCESSION OF IRON OXIDE MICROBIAL MATS IN ACIDIC GEOTHERMAL SPRINGS

Paper number: 2-1
Program: Technical Sessions
Time: 8:00 AM – 8:20 AM

Authors

Abstract

Iron oxide microbial mats are ubiquitous in nature and are potentially important modern analogues of ancient microbial ecosystems. Amorphous iron oxyhydroxide microbial mats that form in acidic geothermal outflow channels of Yellowstone National Park (YNP) contain autotrophic and heterotrophic microbial populations from the domains Archaea and Bacteria. Although these iron oxide mat systems have been well characterized, mechanisms of their formation and growth are poorly understood. Therefore, the goal of this study was to determine the major biological and physicochemical factors contributing to the in situ development of iron oxide microbial mats in acidic hot springs of YNP.

Iron oxide microbial mat development was studied by inserting glass microscope slides into high temperature (65-73 °C), acidic (pH = 3-3.5) hot spring outflow channels. Slides were removed at various time points to determine microbial community structure (16S rRNA gene) and microscopy (e.g., SEM) in combination with total iron oxide accretion measurements. Routine physicochemical parameters (e.g., flow) were also measured to determine their relative contribution to mat development.

Autotrophic bacteria (i.e., Hydrogenobaculum) were first to colonize glass slides (< 4 days) and autotrophic, iron-oxidizing archaea (e.g., Metallosphaera) appeared > 4 days, coinciding with iron oxide accretion. Heterotrophic taxa colonized after ~ 3 weeks of mat growth, which likely corresponds with organic carbon from autotrophs. Iron oxide accretion rates were slower in summer versus winter months. This seasonal variability is likely attributed to cellular stress caused by UV irradiation and subsequent viral pressure observed in SEM during summer months. High velocity flow channels also exhibited a negative effect on iron oxide accretion rates. This study revealed that a combination of biological and hydrodynamic feedback mechanisms control the formation of iron oxide microbial mats in acidic hot springs.