Notes

Outline

Deep Secrets from the Marine Microbial Food Web David Karl SOEST

ACKNOWLEDGMENTS Ed Laws /    Raleigh Hood Joanie Kleypas My lab

OUTLINE Pre-JGOFS view of the marine microbial food web New knowledge gained during JGOFS-era Critical knowledge gaps Future research prospectus

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"THE IMMEDIATE TASKS OF MARINE MICROBIOLOGY" (KRISS, 1963) Extension of at-sea observations and integration into "mainstream" oceanography, especially marine geochemistry Year-round, repeat observations to resolve daily, seasonal and interannual variations Estimation of productivity and determination of controls on P:B ratios Begin systematic study of bacterial taxonomy, especially in "bathysphere" (i.e., deep sea)

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R. W. EPPLEY, ca. 1984

PARADIGMS ca. 1985 Climax community in ocean gyres (McGowan, Hayward, Venrick et al.) Fixed ecological stoichiometry     (Redfield et al.) New (NO3-) and regenerated (NH4+) production (Dugdale & Goering) Export vs. PP (Eppley & Peterson) Fixed subeuphotic zone remineralization (Martin et al.)

NOVEL MICROBES, NOVEL ECOLOGIES 1988:  Prochlorococcus (Chisholm) 1992:  pelagic Archaea (DeLong/Fuhrman) 2000:  rhodopsin-containing photoheterotrophs (Béjà and DeLong) 2000:  rediscovery of anaerobic anoxygenic phototrophs (Kolber and Falkowski) 2002:  SAR 11 (Rappé and Giovannoni) 2002 and beyond:  ??

PROKARYOTE POWER Large percentage of genome is devoted to metabolic regulation - large potential for "habitat tuning" Direct exchange of "free DNA" (new genetic information) between and among otherwise unrelated prokaryotes (transformation) is commonplace in nature "Species concept" uncertain

"Less than 1%" Less than 1% of species Only 1 "model" system

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WHAT SHOULD WE MEASURE? DNA/RNA (genomics, community structure) Cell numbers Cell biomass (as C) and C-N-P Metabolic activity, cell division, growth rate Biomass production (as C) Gross or net metabolic processes

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SOME NEW KNOWLEDGE GAINED DURING THE JGOFS-ERA Microbial biodiversity -> biocomplexity and importance of community structure Violation of "Redfield rules" of microbial production stoichiometry Multiple nutrient co-limitation and P-Fe-N2 syntrophy Vitamin "ecology"

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HOT CORE PARAMETERS Systematic drawdown (by 70%) of inorganic-P over past decade Systematic increase (by 50%) of N2 fixation over past decade Variable phytoplankton community structure, but NO CHANGE IN PP!

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"PRIMARY" PRODUCTION (14C INCORPORATION) QUESTIONS How important are non-carbon dioxide fixing phototrophs? Why is PP constant despite large changes in community structure and nutrient inventories? Why is PP uncorrelated with C-export? What limits PP? Is there a better method to estimate total bio-photo-energy flux?

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A SEA OF DICHOTOMY

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DIVERSITY OF N2 FIXERS AT STA. ALOHA

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ECOLOGICAL STOICHIOMETRY:  FROM REDFIELD TO FARFIELD

VITAMIN ECOLOGY Most eukaryotes (especially diatoms) are vitamin (especially B1, B12) auxotrophs Most prokaryotes (especially heterotrophic bacteria) can synthesize their own vitamins and then some Vitamins (especially B1 and B12) are present in limiting concentrations in subtropical and Southern Ocean habitats

VITAMIN ECOLOGY Vitamin bioavailability controls community structure Vitamin syntrophy controls primary carbon fixation and export

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JGOFS "MARCHING ORDERS" REDUCING UNCERTAINTIES To determine and understand on a global scale the processes controlling time-varying fluxes of carbon and associated biogenic elements To develop a capability to predict the response of oceanic biogeochemical processes to natural and anthropogenic perturbations

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EVERYTHING OLD IS NEW AGAIN! JGOFS-SMP 2002 Taxonomy:  Genome sequencing, bioinformatics, proteomics Biochemistry:  Novel energy transduction pathways, biodegradation of "recalcitrant" DOM Physiology:  N2 fixation, anoxygenic phototrophy/photoheterotrophy, stoichiometry Ecology:  Symbiosis, niche partitioning, competition, natural selection

A FEW GUIDING PRINCIPLES FOR THE FUTURE Microbial IS NOT = bacterial Availability of field methods limits progress Habitats are diverse and variable in space and time Accurate models do not exist

POST-JGOFS CRITICAL KNOWLEDGE GAPS:  MICROBIOLOGY/PHYSIOLOGY Species ID and enumeration Gene expression and regulation Syntrophy/symbiosis/competition

POST-JGOFS CRITICAL KNOWLEDGE GAPS:  ECOLOGY/BIOGEOCHEMISTRY PP - flux - flux attrition Plasticity of ecological stoichiometry N2 fixation – denitrification Carbon AND energy fluxes Compound-specific DOM analyses

R. W. EPPLEY, ca. 1984

D. M. KARL, ca. 2002

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