C-DEBI Newsletter – April 15, 2015

Hot off the press: Data report: dissolved and particulate organic carbon in the deep sediments of IODP Site U1363 near Grizzly Bare seamount (C-DEBI Contribution 236) in Proceedings of the IODP Volume 327
Authors: C-DEBI researchers Lin, Hsieh, Cowen and Rappé. Abstract: Marine sediments are a primary reservoir for the long-term storage of organic matter, and the rate of burial and oxidation of this sedimentary organic material help to regulate both atmospheric oxygen and carbon dioxide concentrations. To evaluate the impact of circulating basement fluid on the preservation of deeply buried organic carbon, sedimentary profiles of dissolved and particulate organic carbon (DOC and POC) near the sediment/basement interface were obtained from sediment coring at Site U1363 during Integrated Ocean Drilling Program Expedition 327. Sedimentary DOC increased from 0.25 mM at 1 m below the seawater/sediment interface to a maximum of 0.86 mM at mid-depth (8–11 meters below seafloor [mbsf]), before subsequently decreasing to a minimum of 0.10 mM at the sediment/basement interface (222.7 mbsf). Thus, the oceanic basement appears to be a net sink for sedimentary DOC. Sedimentary DOC and alkalinity profiles were similar and inversely mirror those of sulfate, suggesting that the buildup of DOC in sediment pore water is related to remineralization of sedimentary POC. The sedimentary POC content at Site U1363 ranged from 47 to 391 µmol-C/g, with δ¹³C values from –25.3‰ to –22.4‰. The total particulate nitrogen (PN) content ranged from 4.1 to 32.9 µmol-N/g, with δ¹⁵N values from 1.8‰ to 7.2‰ and a POC:PN ratio of 12 ± 2 (n = 54). No depth-specific systematic variations in POC, PN, POC:PN ratio, δ¹³C-POC or δ¹⁵N-PN were detected, and no significant correlations between sedimentary DOC and POC concentrations were observed.

Hot off the press: Catabolic rates, population sizes and doubling/replacement times of microorganisms in natural settings (C-DEBI contribution 234) in American Journal of Science
Authors: C-DEBI researcher LaRowe and director Amend. Abstract: Directly assessing the impact of subsurface microbial activity on global element cycles is complicated by the inaccessibility of most deep biospheres and the difficulty of growing representative cultivars in the laboratory. In order to constrain the rates of biogeochemical processes in such settings, a quantitative relationship between rates of microbial catalysis, energy supply and demand and population size has been developed that complements the limited biogeochemical data describing subsurface environments. Within this formulation, rates of biomass change are determined as a function of the proportion of catabolic power that is converted into anabolism—either new microorganisms or the replacement of existing cell components—and the amount of energy that is required to synthesize biomass. Catabolic power is related to biomass through an energy-based yield coefficient that takes into account the constraints that different environments impose on biomolecule synthesis; this method is compared to other approaches for determining yield coefficients. Furthermore, so-called microbial maintenance energies that have been reported in the literature, which span many orders of magnitude, are reviewed. The equations developed in this study are used to demonstrate the interrelatedness of catabolic reaction rates, Gibbs energy of reaction, maintenance energy, biomass yield coefficients, microbial population sizes and doubling/replacement times. The number of microorganisms that can be supported by particular combinations of energy supply and demand is illustrated as a function of the catabolic rates in marine environments. Replacement/doubling times for various population sizes are shown as well. Finally, cell count and geochemical data describing two marine sedimentary environments in the South Pacific Gyre and the Peru Margin are used to constrain in situ metabolic and catabolic rates. The formulations developed in this study can be used to better define the limits and extent of life because they are valid for any metabolism under any set of conditions.

Frontiers in Microbiology: Seeking Contributions for Special Topic on Ocean Crust Geomicrobiology
A special issue of Frontiers in Microbiology journal on the topic of “Recent Advances in Geomicrobiology of the Ocean Crust” is seeking contributions from the C-DEBI community. Articles in the research topic are in tribute to the late Katrina J. Edwards, who was a pioneer in diverse aspects of exploring life in oceanic crust. For more information, contact topic editors Beth Orcutt, Cara Santelli, or Jason Sylvan, or visit the journal webpage. Abstracts due April 16, 2015.

IODP: Apply to sail on Expedition 364 Chicxulub Impact Crater
The deadline to apply is May 08, 2015. To learn more about the scientific objectives of this expedition, life at sea, and how to apply to sail, please join the ECORD Science Operator for a web-based seminar on Tuesday, April 21, 2015 at 9am EDT. To register, please visit: https://www.surveymonkey.com/s/IODP364.

DCO: Deep Life Community Call for Proposals 
Application deadline: May 01, 2015.

National Academies: Research Associateships for Graduate, Postdoctoral and Senior Researchers
There are four annual review cycles and the next closes May 01, 2015.

IODP-USSSP: Proposals for Pre-Drilling Activities and Workshops
The U.S. Science Support Program (USSSP) accepts proposals on a rolling basis for pre-drilling activities and semi-annually for workshops, next submission deadline May 15, 2015, related to the International Ocean Discovery Program (IODP).

DCO: Call for Proposals Census of Deep Life Sequencing Opportunities
Application deadline: June 01, 2015.

Meetings, Workshops and Activities