Soil/Rhizosphere Microorganisms are responsible for most nutrient transformation in soil. 10 9 cells and 10 6 distinct taxa per g of soil. Different plants have different root exudates (up to 20% of photosynthate). Arabidopsis does not grow in g-irradiated soil
From the first land plants to cereals and legumes First land plant used AM fungi as rooting systems Legume Family (Leguminosae) 3 rd largest family of plants 19,400 species Legumes have symbiosis with bacteria (the rhizobia)
From the first land plants to cereals and legumes First land plant used AM fungi as rooting systems Legume Family (Leguminosae) 3 rd largest family of plants 19,400 species Legumes have symbiosis with bacteria (the rhizobia)
The Players + = Soybean Bradyrhizobium japonicum N 2 fixation in nodules Soybeans twice protein per acre as any other major vegetable or grain crop, 5 to 10 times than land used for dairy, and 15 times land for meat production.
Nitrogen cycle Nitrogen cycles between inert N 2 and biologically available NH 3 Nitrogen main limiter of biological production 50-60% of biospheres nitrogen comes bacterial N 2 fixation in legume nodules
Pisum sativum 7 chromosomes diploid 5 Gbp (human 3.2 Gbp) Mendel examined 7 traits on 4 chromosomes Bateson championed Mendel s work and coined Genetics
European civilisation and legumes Umberto Eco considers the bean saved Western civilisation (New York Times) From 1000-1500AD Europe's population tripled because of bean cultivation (Animal manure not sufficient)
Oil of the 19 th century Chincha Islands Guano War of the Pacific 1879-1883
Greatest Scientific development in last 200 years? It is the chemist who must come to the rescue of the threatened communities Sir William Crookes 1898 to BAAS N 2 (g) + 3H 2 (g) 2NH 3 (g), ΔH = 92.4 kjmol -1 CH 4 + H 2 O CO + 3H 2 Haber discovered 1909 Nobel prize 1918 Bosch scaled up and won Nobel in 1931
Nitrogen and population Addition of nitrogen and phosphorous: Haber Bosch process 1909 Dwarf varieties of wheat and rice (short stem, large grain): Green revolution 1960 s
Nitrogen cascade Massive application of Haber-Bosch Nitrogen for agriculture (120 Mt year) Reactive Nitrogen in biosphere now 2X pre-industrial level Nitrate leaches to ground water Denitrifiers convert excess soil ammonia to N 2 O (nitrous oxide) N 2 O 300X more potent greenhouse gas than CO 2
Rockstrom et al. Nature 2009: 473
Global grain yields
Nutrient limitation A=maize B=wheat C=rice Mueller et al. Nature 490, 254 (2012)
We have a problem
Nitrogen cycle Nitrogen cycles between inert N 2 and biologically available NH 3 50-60% of biospheres nitrogen comes bacterial N 2 fixation in legume nodules Nitrogen main limiter of biological production
Getting inside a nodule Gage and Margolin Current Opinions in Microbiology 2000, 3: 613-617
Nod Factor Nodulation signalling pathway (shared with mycorrihzal fungi) Receptors LRR-kinase Cation channel Nucleoporins Ca ++ spiking CCaMK TFs Nod Gene induction TFs Myc Gene induction Myc Factor
The exchange that limits life Ile Leu Val Sst1 SO 4 2- Malate Dct? Aap Bra? MoO 4 2 -? DctA Pyr Ala Acetyl- CoA OAA TCA cycle Mol Dmt1? Fe 2+ Symbiotic plant cell CO 2 Oxaloacetate PEP Hexoses Aap Bra MgtE Mg 2 + PH B e - & ATP? H + H + H + H + ATP ADP+ P i? Nitogenase complex? Amino acid pool GS/ GOGAT N 2 NH 3 Bac A Acetyl-CoA Fen1 Homocitrate α-ketoglutarate H + NH 4 + golgi NCR Glu GS SPC ER Gln AS nucleus Asn Udvardi and Poole, Downie Annu Rev Plant Biology (2013)
ENGINEERING SYNTHETIC SYMBIOSES Engineer tailored nitrogen-fixing plant microbe associations using established endophytic plant microbes Engineer nodules onto cereals Express nitrogenase in plant plastids
Natural solutions Eat legumes not meat and dairy Improve use and efficiency of legumes
Beans in Africa
Problem with beans Beans in Africa get nodulated by rhizobia that fix little nitrogen How can we identify the good nitrogen fixing bacteria?
Glowing bacteria light up nodules nifh::luxcdabe fusion in pea/bean nodulating bacteria Bacteria glow when they fix N 2, i.e. report how effective
Acknowledgements Vinoy Ramachandran Alison East Izzy Webb Jason Terpollili Kushboo Boorah Rachel Wheatley Barney Geddes Amelie Joffrin Ponraj Paramasivan (Cambridge) Nick Kruger George Ratcliffe Stuart Conway Giles Oldroyd (Cambridge)