Abstract
Microbial communities in hydrothermal systems exist in a range of macroscopic morphologies including stromatolites, mats, and filaments. The architects of these structures are typically autotrophic, serving as primary producers. Structures attributed to microbial life have been documented in the rock record dating back to the Archean including recent reports of microbially-related structures in terrestrial hot springs that date back as far as 3.5 Ga. Microbial structures exhibit a range of complexity from filaments to more complex mats and stromatolites and the complexity impacts preservation potential. As a result, interpretation of these structures in the rock record relies on isotopic signatures in combination with overall morphology and paleoenvironmental setting. However, the relationships between morphology, microbial community composition, and primary productivity remain poorly constrained. To begin to address this gap, we examined community composition and carbon fixation in filaments, mats, and stromatolites from the Greater Obsidian Pool Area (GOPA) of the Mud Volcano Area, Yellowstone National Park, WY. We targeted morphologies dominated by bacterial phototrophs located in close proximity within the same pool which are exposed to similar geochemistry as well as bacterial mat, algal filament and chemotrophic filaments from nearby springs. Our results indicate i) natural abundance δ13C values of biomass from these features (-11.0 to -24.3 ‰) are similar to those found in the rock record; ii) carbon uptake rates of photoautotrophic communities is greater than chemoautotrophic; iii) oxygenic photosynthesis, anoxygenic photosynthesis, and chemoautotrophy often contribute to carbon fixation within the same morphology; and iv) increasing phototrophic biofilm complexity corresponds to a significant decrease in rates of carbon fixation—filaments had the highest uptake rates whereas carbon fixation by stromatolites was significantly lower. Our data highlight important differences in primary productivity between structures despite indistinguishable δ13C values of the biomass. Furthermore, low primary productivity by stromatolites compared to other structures underscores the need to consider a larger role for microbial mats and filaments in carbon fixation and O2 generation during the Archean and Proterozoic.
Highlights
Physical structures of extant microbial communities include filaments, microbial mats, and stromatolites
We targeted a site at Greater Obsidian Pool Area (GOPA) in which phototrophic filaments, mats and stromatolites grow within close proximity (Sites 1 contains green filaments (1A)–D) (Figure 1)
Three nearby sites were sampled which each contained a single type of microbial structure: An upstream hot spring that contained a green phototrophic mat (Site 2; Figure 1); purple phototrophic filaments from a nearby pool (Site 3; Figure 1); and gray chemotrophic filaments were collected from a site downstream (Site 4) (Figure 1)
Summary
Physical structures of extant microbial communities include filaments, microbial mats, and stromatolites. These structures are common in a range of environments including hydrothermal features and are comprised of diverse microbial assemblages. Microbial mats, and stromatolites have been found in the ancient rock record (e.g., Logan et al, 1964; Schopf, 1993; Allwood et al, 2006; Noffke et al, 2006; Schopf et al, 2007) and provide evidence for the presence of life including the recent discovery of microbial structures in terrestrial hydrothermal systems dating to 3.5 Ga (Djokic et al, 2017). Taxonomic or morphological signatures could aid in determining the prevailing environmental conditions and biogeochemical cycling at the time of formation and deposition
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
