TY  - JOUR
A1  - Nagakura, Toshiki
A1  - Schubert, Florian
A1  - Wagner, Dirk
A1  - Kallmeyer, Jens
T1  - Biological sulfate reduction in deep subseafloor sediment of Guaymas Basin
JF  - Frontiers in microbiology
N2  - Sulfate reduction is the quantitatively most important process to degrade organic matter in anoxic marine sediment and has been studied intensively in a variety of settings. Guaymas Basin, a young marginal ocean basin, offers the unique opportunity to study sulfate reduction in an environment characterized by organic-rich sediment, high sedimentation rates, and high geothermal gradients (100-958 degrees C km(-1)). We measured sulfate reduction rates (SRR) in samples taken during the International Ocean Discovery Program (IODP) Expedition 385 using incubation experiments with radiolabeled (SO42-)-S-35 carried out at in situ pressure and temperature. The highest SRR (387 nmol cm(-3) d(-1)) was recorded in near-surface sediments from Site U1548C, which had the steepest geothermal gradient (958 degrees C km(-1)). At this site, SRR were generally over an order of magnitude higher than at similar depths at other sites (e.g., 387-157 nmol cm(-3) d(-1) at 1.9 mbsf from Site U1548C vs. 46-1.0 nmol cm(-3) d(-1) at 2.1 mbsf from Site U1552B). Site U1546D is characterized by a sill intrusion, but it had already reached thermal equilibrium and SRR were in the same range as nearby Site U1545C, which is minimally affected by sills. The wide temperature range observed at each drill site suggests major shifts in microbial community composition with very different temperature optima but awaits confirmation by molecular biological analyses. At the transition between the mesophilic and thermophilic range around 40 degrees C-60 degrees C, sulfate-reducing activity appears to be decreased, particularly in more oligotrophic settings, but shows a slight recovery at higher temperatures.
KW  - sulfate reduction
KW  - subsurface life
KW  - deep biosphere
KW  - thermophiles;
KW  - Guaymas Basin
Y1  - 2022
U6  - https://doi.org/10.3389/fmicb.2022.845250
SN  - 1664-302X
VL  - 13
PB  - Frontiers Media
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Kallmeyer, Jens
A1  - Pockalny, Robert
A1  - Adhikari, Rishi Ram
A1  - Smith, David C.
A1  - D'Hondt, Steven
T1  - Global distribution of microbial abundance and biomass in subseafloor sediment
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - The global geographic distribution of subseafloor sedimentary microbes and the cause(s) of that distribution are largely unexplored. Here, we show that total microbial cell abundance in subseafloor sediment varies between sites by ca. five orders of magnitude. This variation is strongly correlated with mean sedimentation rate and distance from land. Based on these correlations, we estimate global subseafloor sedimentary microbial abundance to be 2.9 center dot 10(29) cells [corresponding to 4.1 petagram (Pg) C and similar to 0.6% of Earth's total living biomass]. This estimate of subseafloor sedimentary microbial abundance is roughly equal to previous estimates of total microbial abundance in seawater and total microbial abundance in soil. It is much lower than previous estimates of subseafloor sedimentary microbial abundance. In consequence, we estimate Earth's total number of microbes and total living biomass to be, respectively, 50-78% and 10-45% lower than previous estimates.
KW  - deep biosphere
KW  - cell enumeration
KW  - global microbial biomass
KW  - subsurface life
Y1  - 2012
U6  - https://doi.org/10.1073/pnas.1203849109
SN  - 0027-8424
VL  - 109
IS  - 40
SP  - 16213
EP  - 16216
PB  - National Acad. of Sciences
CY  - Washington
ER  -