Microscale Biosignatures and Abiotic Mineral Authigenesis in Little Hot Creek, California

Abstract

Hot spring environments can create physical and chemical gradients favorable for unique microbial life. They can also include authigenic mineral precipitates that may preserve signs of biological activity on Earth and possibly other planets. The abiogenic or biogenic origins of such precipitates can be difficult to discern, therefore a better understanding of mineral formation processes is critical for the accurate interpretation of biosignatures from hot springs. Little Hot Creek (LHC) is a hot spring complex located in the Long Valley Caldera, California, that contains mineral precipitates composed of a carbonate base (largely submerged) topped by amorphous silica (largely emergent). The precipitates occur in close association with microbial mats and biofilms. Geological, geochemical, and microbiological data are consistent with mineral formation via degassing and evaporation rather than direct microbial involvement. However, the microfabric of the silica portion is stromatolitic in nature (i.e., wavy and finely laminated), suggesting that abiogenic mineralization has the potential to preserve textural biosignatures. Although geochemical and petrographic evidence suggests the calcite base was precipitated via abiogenic processes, endolithic microbial communities modified the structure of the calcite crystals, producing a textural biosignature. Our results reveal that even when mineral precipitation is largely abiogenic, the potential to preserve biosignatures in hot spring settings is high. The features found in the LHC structures may provide insight into the biogenicity of ancient Earth and extraterrestrial rocks.

Growth morphologies and plausible stressors ruling the formation of Late Pleistocene lacustrine carbonate buildups in the Maquinchao Basin (Argentina)

“…Although associated with micrite, filament-like porosity in the Maquinchao samples seems to be unrelated to porosity. Furthermore, micro-boring organisms can be a source of micritization (Bathurst, 1966;Kraus et al, 2018) but this does not appear to be the case in this study as the micrite is very homogeneous and, therefore, unlikely to result from micro-boring. In the analysed samples, filaments were observed that are mostly vertically erected with no ramifications.…”

“…Filaments of around 5-10 µm width have been identified as different microorganisms, mostly cyanobacteria such as Oscillatoria, Phormidium, Schizothrix or Rivularia, especially in fluviatile and lacustrine systems (Freytet & Plet, 1996;Freytet & Verrecchia, 1998). Nevertheless, Kraus, Beeler, Mors, Floyd, and Stamps (2018) has demonstrated that vertical tubular porosity can be associated with micro-boring by microorganisms. Although associated with micrite, filament-like porosity in the Maquinchao samples seems to be unrelated to porosity.…”

In situ Linkage of Fungal and Bacterial Proliferation to Microbiologically Influenced Corrosion in B20 Biodiesel Storage Tanks

“…Libraries of bacterial, archaeal, and eukaryotic small subunit (SSU) rRNA gene fragments were amplified from each DNA extraction using a single set of PCR with primers that spanned the SSU rRNA gene V4/V5 hypervariable regions between position 515 and 926 (E. coli numbering) as described previously (Parada et al, 2015;Kraus et al, 2018). The primers used were selected to evenly amplify all three domains of life simultaneously (Parada et al, 2015).…”

Assessing and Maximizing Cultivated Diversity with Plate-Wash PCR and High Throughput Sequencing

“…These primers produced two amplicons, a ~400 bp fragment for bacteria and archaea, and a 600 bp fragment for eukaryotes. The forward primer 515F-Y (5’- GTA AAA CGA CGG CCA G CCG TGY CAG CMG CCG CGG TAA-3’) contains the M13 tag (underlined) fused to the 5’ end of the forward primer (41). The reverse primer 926R (5’-CCG YCA ATT YMT TTR AGT TT-3’) was unmodified from Parada et.…”