The Oceanic Biogeochemical Carbon Cycle Bacterial adaptations to the ocean Ecosystem functions of marine microbes: Bacterial role in how the ocean works as a biogeochemical system Marine microbes’ influence on global habitability

Are microbes important as a biogeochemical force Are microbes important as a biogeochemical force? Microbes have been profoundly shaping the Earth’s environment “Our” Earth is a microbial planet -- and we as a biogeochemical force are changing their habitats . Will they respond by changing Earth as our habitat? Madigan, 2008

The Age of Discovery 1977 Bacteria 106 mL-1 (103 x cfu) 79/80 High bacterial growth & C demand (dynamic populations) 84 Protozoa (103 mL-1) major predators on bacteria 79-90 Viruses abundant (107 mL-1) & major predators on bacteria 79 Synechococcus 103 - 105 mL-1 88 Prochlorococcus 104 - 105 mL-1 90-07 Remarkable widespread Archaea throughout the oceans (104 - 105 mL-1) Discovery of anoxygenic photosynthetic bacteria Rise of molecular ecology Massive marine genomics and metagenomics-- providing constrains for diversity and ecosystem function. Now, faster sequencing (454--?) Culturing the “unculturable” Widespread picoeukaryotes Discovery of diverse bacteriorhodopsins Many more: e.g. SO4-reducing methanotrophs; ammonox; Fe-protein-dominated (86%) cellular machinery of Ferroplasma acidiphilum

We have been discussing: Bacteria-OM interactions structure marine ecosystems at nm scale- one molecule at a time. But is bacteria-OM coupling at fine (biochemical) scale useful in ocean basin scale C fluxes? Azam and Malfatti, 2007 Nature Reviews Microbiology 10:782 Swimming stomachs Significance of spatial coupling Cell surface hydrolases; 102-104 x variability in cell-specific activity High affinity + high capacity permeases Biodiversity --> Biochemical diversity

Biogeochemical integrative view: How much of the FIXED CARBON does go into: 1) Bacteria? 2) Fish? 3) Bottom sediments? CO2 CH4 Azam and Malfatti, 2007 Nature Reviews Microbiology 10:782

Bacterial Carbon Demand is a Major and Variable Flux Pathway--> variability of biogeochemical state -> Variability in Bact-OM coupling strength:consequences 3H- Thymidine or Leu for µ & BCP BCD=BCP + R Modified from Cole et al, 1988 MEPS. 43: 1-10. * Smith et al, 1995 (mesocosm bloom) ** Pomeroy & Deilbel, 1986 (New Foundland coast) Turley et al, 1999 (E Med Fc =0.85) Mesopelagial: >80% C flux-> Bacteria (Cho and Azam, 1988) Sewage outfalls and aquaculture: Fc >1 Too high Fc may kill corals! Coupling variability of Bacteria-OM What causes it? Biochemistry happens! Will return to this issue; but first: why care?

How much into Bacteria, Fish and Sediment? We are living in a 401.52 ppm CO2 world (http://keelingcurve.ucsd.edu/):

For a few CYCLES more (all IS connected): Carbon Nitrogen Iron Sulfur Phosphate Pollutants Redfield ratio or Redfield stoichiometry is the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton and throughout the deep oceans C:N:P = 106:16:1 (Redfield A.C. 1934)

Carbon transformations in the environment Figure: 19-23 Caption: Redox cycle for carbon; note in particular the contrasts between autotrophic (CO2 organic compounds) and heterotrophic processes. Yellow arrows indicate oxidations; red arrows indicate reductions. Photosynthesis in oxic habitats is mainly oxygenic, whereas in anoxic environments it is mainly anoxygenic from the activities of purple and green bacteria. Under anoxic conditions, besides homoacetogens and methanogens, certain sulfate-reducing and nitrate-reducing bacteria are also autotrophic. Methanogens make methane, whereas methanotrophs consume methane. Madigan 10th edition

In the ocean The Solubility Pump The Biological Pump C fixed mostly by photosynthesis Locally important C fixation by chemolithotrophs Munn, 2004

The Nitrogen cycle Figure: 19-29right Caption: Redox cycle for nitrogen. Oxidation reactions are represented by yellow arrows and reductions in red. N is one of the most important growth limiting nutrients for phytoplankton and bacteria Madigan 10th edition

Iron Fluxes in the environment Low solubility of ferric iron, precipitation as oxide Acidic environment, food vacuoles of protists Fe is one of the most important growth limiting micro-nutrients for phytoplankton and bacteria Cellular respiration (S-Fe protein complex) HNLC areas, such as Southern Ocean, are Fe limited Fe fertilization for CO2 sequestration in order to reduce CO2 in the atmosphere Munn, 2004 Madigan 10th edition

Sulfur Cycle Archaea and SRB Syntrophy: marine microbial consortium that mediates anaerobic oxidation of methane Sulfur Cycle Archaea and SRB Figure: 19-25 Caption: Anoxic methane oxidation. (a) Methane-oxidizing cell aggregates from marine sediments. The aggregates contain methanogenic bacteria (red) surrounded by sulfate-reducing bacteria (green). Each cell type is stained by a different phylogenetic FISH stain (Section 18.4). (b) Possible mechanism for syntrophic anoxic methane oxidation in the cell aggregates. Influence on climate in the bacteria-phytoplankton interaction: DMS (dimethyl sulfide) is a breakdown product from DMSP (dimethylsulfoniopropionate) and also from DMSO (dimethyl sulfoxide). DMS act as cloud condensation nuclei DMSP is an osmolyte prodcuded by phytoplankton Madigan 10th edition and Boetius et al. 2000

P-cycling http://jpkc.nwu.edu.cn/ At low Pi bacteria are avid competitors with phytoplankton At hight Pi the situation is reversed Explained by biochemistry of flux coupling Implication for f-ratio for P (eg: Mediterranean Sea) Ammerman et al. 1984. MEPS 18:31-39 Ammerman & Azam 1985. Science 227:1335-1340 Paul et al. 1988. AEM 54:1682-1688 Thingstad & Rassoulzadagan 1999. Prog. Oceanogr. Azam et el. 1999 (Aggregation may enhance P-cycling rate) http://jpkc.nwu.edu.cn/