Juan Imperial's talk at the 1st Earth Microbiome Meeting in Shenzhen

1. Soil Metagenomics of the Legume-Rhizobial Symbiosis Rhizobium Genomics Group (RHIZOGEN)Centro de Biotecnología y Genómica de Plantas (CBGP)UPM-INIA (CSIC), Madrid, Spain

2. Legumeand Rhizobia:A root nodule symbiosis …

3. … thatfixesnitrogen

4. AgriculturalImportance of Legumes 2ndaftercereals (above 11% cultivatedland) Protein and oil-rich: mainsource of proteinfor animal feed Alsoused as forage, often in rotationwithcereals, wheretheyenrichthesoilforthe cereal crop Onlymajoragriculturalcropsproviding a self-sufficient, sustainable input of fixedNitrogentoagriculturalsystems

5. N2fixationbylegumes 50 Tg

6. Therhizobial-legumesymbiosis Veryspecific: co-evolution of plants and bacteria Controlledbytheplant, providingan ideal niche fortheanaerobicprocess of nitrogenfixationwithintherootnodule As a result, thelegumeplantbecomesindependent of anyexternalsource of fixed N As a result, therhizobiathrive in a protectedenvironment, thusmaintaining and increasingtheirnumbers in soil O2 Photosynthate N2 NH4+

7. Rhizobia as soil bacteria Rhizobia are soil bacteria devoting a verysmallpercentage of theirverylargegenometothesymbioticdeterminants Foranygivenlegume, efficient, inefficient, and non symbioticrhizobiaco-exist in thesamesoil Inefficientrhizobiahighlyadaptedto a specificsoilusuallyoutperformefficientlaboratorystrains in theircolonization of theirlegumeplant host. Thisis a source of trouble (inoculation) and a potentialarea of improvement Clear-cut case formetagenomicstudy of soil and rhizosphericrhizobialpopulations. However …

8. Rhizobiumis a minorsoilinhabitant ≈104R. leguminosarumbv. viciae viable cells per g soil MPN planttrapmethod: onlysymbioticrhizobiaisolated Directisolationmethod: bothsymbiotic and non-symbioticrhizobiaisolated (1:3 ratio) Thisis ≈ 0.1% viable bacteria per g soil ≈105R. leguminosarumbv. viciae viable cells per g host legumerhizospheresoil Are standardmetagenomicstrategiesappropriate?

9. Ourcurrentprojects. 1 Genomicdeterminants of rhizobialgenotypeselectionbythe host LensPisumVicia sativa Vicia faba Lathyrus R. leguminosarum bv. viciae, 7.8 Mb

10. Ourcurrentprojects. 2 Rhizobialadaptationto a recentlydescoveredlupinspecies: Lupinusmariae-josephae, growingonbasicsoils in Eastern Spain: onlylupinfrombasicsoils Notnodulatedbyrhizobiafromother, acidiclupins Nodulatedby novel rhizobia, foundwiththeplant in itsendemicregion, rhizobianodulatingRetama in basicsoils of NorthenAlgeria, and in basicsoils of Chiapas (Mexico) Metagenomic, comparativestudies of thesebasicsoils are obviouslyinteresting, butwilltheyprovideusefulinformationontherhizobia?

11. Ourcurrentprojects. 3 H ROOT ROOT 2 ENERGY ENERGY H 2 HUP N ase 2 N ase 2 organic organic N N + + NH NH N N 4 4 2 2 25% electronsfedtonitrogenaseend up as H2 as a result of thecatalyticmechanism of theenzyme Hup+ rhizobia (rare) recyclethis H2, thusincreasingtheenergyefficiency of thesymbiosis However, theproductionorabsence of H2also has aneffectonthesoilmicrobiome (increase in hydrogen-assimilating bacteria) Amenableto“standard” soilmetagenomicsexperiments Hup- Hup+

12. CENTRO DE BIOTECNOLOGÍA Y GENÓMICA DE PLANTASUPM – INIAMONTEGANCEDO (MADRID, SPAIN)WWW.CBGP.UPM.ES