SULFUR BIOSIGNATURES IN CONTINENTAL HOT SPRING, STREAM AND CRATER LAKE SEDIMENTS AFFECTED BY HYDROTHERMAL H2S GAS EMISSION

Anna Szynkiewicz (1) and Jill Mikucki (2)1) Department of Earth & Planetary Sciences, University of Tennessee; (2) Department of Microbiology, University of Tennessee.

The presence of sulfur (S) compounds on Mars has been commonly linked to hydrothermal activity in the past when Mars was more volcanically active and water was stable on the surface.

Similarly, gas- and dissolved-phase S-bearing compounds are abundant at modern volcanic systems on Earth, particularly continental springs where hydrothermal water discharges on land. These habitats support diverse microbial ecosystems that host metabolic communities capable of S oxidation and reduction (i.e. redox reactions) for energy.

Therefore, investigating biosignatures associated with hydrothermal microbial S cycling on Earth is critical for identifying potentially similar biosignatures on Mars.

INTRODUCTION

Figure 5. Phylogenetic tree of aprA sequences from Valles Caldera sediments and the most identical cultured organisms that contain these genes and environmental sequences. Scale bar indicates the branch length corresponding to 0.05 substitutions per amino acid.

ACKNOWLEDGMENTS: This study is supported by NASA award No. NNX14AB63G.

A

340 km

New Mexico

Texas

Mexico

Colorado

Mexico

Rio Grande Rift

VC

Rio Chama

Rio

Gra

nde

Jemez River RI

O G

RA

ND

E RI

FT

VALLESCALDERA

The 22 km-wide Valles Caldera of northern New Mexico (Fig. 1A, 2) has hosted volcanic and geothermal activity since the last caldera-forming eruption at 1.25 Ma. Active H2S-rich fumaroles and hot springs manifest in the western portion of caldera at Sulphur Springs (Fig. 1B-C).

Figure 1. (A) Location of Valles Caldera with its position relative to the Rio Grande rift (Courtesy of Phil Miller and New Mexico Bureau of Geology and Mineral Resources). (B-C) Examples of CO2 and H2S hydrothermal gas emissions in the Sulphur Springs area.

MARS ANALOG - VALLES CALDERA

B CSULPHUR CREEKH2S gets oxidizedin streambed sediments

H2S gets dilutedin atmosphere

Sulp

hur Cre

ek

Alamo Canyon

Redo

ndo

Creek

San Antonio

Jem

ez Rive

r VallesCaldera

S-rich hydrothermal alterations

Caldera

East Fork Jemez

Figure 2. Location of sampling points. Orange and blue dots indicate the streams with low water pH (2 to 5) due to volcanic H2S oxidation and neutral water pH (6 to 8), respectively.

H2S

H2SH2S

OXIDATION IN STREAMBED

SO4

SO4SO4

SO4

INTENSE H2S SMELL ON THE SURFACE DUE TO GAS DISCHARGE

Figure 4. Simplified model of volcanic H2S oxidation to SO4 in aqueous environment.

SO4

SO4

STREAM WATER SO4: 500-1200 mg/LSTREAM WATER H2S: <0.11 mg/L

WATER COLUMN

Figure 3. Variations of SO4 fluxes in the hydrological system of Valles Caldera relative to the distance from Sulphur Springs with highest volcanic S emission.

November 2012May 2013

In this study, we focused on identifying two types of biosignatures in a continental volcanic complex of Valles Caldera, New Mexico:

Metabolic S- S isotope biosignatures - characteristic imprints upon the environment of the processes by which life extracts energy and material resources to sustain itself.

Molecular (genomic) biosignatures - structural, functional, and info-rmation-carrying molecules that characterize life forms and their metabolism.

GOALS

SULPHUR SPRINGS - HOT MUD POTS

Water vapor, CO2 and H2S gases

Sulphur Springs

Between 2007 and 2014, water and sediment samples were collected from hot spring, stream and crater lake sediments affected by hydrothermal H2S gas emission (Fig. 2).

The determined SO4 flux corresponds to the mass of SO4 ions flowing out of the caldera per unit time (Fig. 3).

S sequential extraction was used to characterize isotope composition of mineral phases containing S , S , and S . To link microbial metabolic potential with observed metabolic isotope signatures, we examined the presence of adenosine-5-phosphosulfate (APS) reductase, a gene involved in both dissimilatory (i.e. energy yielding) sulfate reduction or S oxidation reactions.

METHODS & RESEARCH APPROACH

Sulphur Springs

3 5 7 9 11 13 15 18 19 210

2,000

4,000

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8,000

10,000

12,000

14,000

Distance [km]

SULPHUR SPRINGS(mostly hydrothermal H2S oxidation)

SANANTONIOCREEK

JEMEZ RIVER

(total SO4)

Biogenic sulfides with distinctive negative δ S of -40.3 to -9.9‰ were mainly preserved in stream sediments showing small and/or negligible H2S emission.

In hot spring and stream sediments with high H2S emission the δ S of sulfide minerals had higher values of -1.2 to +2.2‰ suggesting greater inputs of inorganic S from hydrothermal H2S gas emission (+0.8 to +4.8 ‰).

The δ S of sulfides from ancient crater lake sediments (~560ka years; Fig. 2) varied in a similar range (-3.9 to +4.0‰) as in the S-rich volcanic bedrock (-2.2 to +3.3‰) and modern hydrothermal H2S gas.

Poor preservation of metabolic S biosignatures in lake sedimentary record resulted either from limited microbial S metabolism or complete microbial transfromation of oxidized S /S species to sulfides.

In regional scale of Valles Caldera (Fig. 2), aqueous SO4 contributions from oxidation of hydrothermal H2S gas accounted for 7-12% under dry and 41% under wet conditions compared to other sources such as low temperature bedrock weathering (hydrothermal sulfides and sulfate minerals) and atmospheric deposition (Fig.3).

Since concentrations of SO4 were always significa-ntly higher compared to H2S (Fig. 4), the majority of volcanic H2S is likely oxidized to SO4 within the streambed.

Total SO4 mass balance in surface water

In Sulphur Springs, DNA extraction and amplification were challenging due to low content. Very low diversity of S-transforming organisms was observed that are potentially quite novel. We were unable to confirm whether their APS reductase is operating in an oxidizing or reducing manner based on phylogenetic distance.

A previous molecular survey by Rzonca & Schulze-Makuch (2003) detected sequences related to S-oxidi-zing acidophiles of the genus Desulfurella and Thioba-cillus. Our results (Fig. 5) further support a biological component to the S signal in Valles Caldara, although the functional role of these microbes remains elusive.

Metabolic 34S-32S isotope biosignatures Molecular (genomic) biosignatures

Crater LakeSediments

Bacteria endosymbiont of Lucinoma aff kazani

Gamma proteobacte rium symbiont of Thyasira

Thiodic tyon & Thiocapsa

Gamma proteobacte rium symbiont of Thyasira

Candidatus Desulfamplus magne tomortis & Desulfobacte rium

Desulfobacte r & Desulfospira

Olavius algarvensis De lta 1 endosymbiont

Desulfonema limicola

Desulfofaba fastidiosa

Desulfofrigus & Desulfococcus

Desulfoce lla & Desulfobotulus

Desulfomicrobium

Desulfovibrio Cluste r 2

Desulfonatronum lacustre & Desulfovibrio Cluste r 1

Desulfobulbus e longatus

Desulfonauticus autotrophicus

Desulfothermus naphthae

Desulfonauticus submarinus

The rmodesulfobium narugense

The rmodesulfovibrio c luste r

Bacterium SM 66 24

SC-1 (8 c lones)

Archaeoglobus Cluste r

Alpha proteobacterium HIMB5

0.05

Sulphur Springs (8 clones)Sulphur Springs (8 clones)

34 32

6+ 0

2-

34

34

34

6+ 0