title: Effect of organic N source on bacterial growth, lipo-chitooligosaccharide production, and early soybean nodulation by Bradyrhizobium japonicum.
abstract: Production of Bradyrhizobium japonicum inoculants is problematic because high inoculation rates are necessary but expensive, while production of rhizobial Nod factors (lipo-chitooligosaccharides (LCOs)), key signal molecules in the establishment of legume-rhizobia symbioses, may be inhibited at high culture cell densities. We conducted experiments to determine the effects of growth medium N source on B. japonicum growth, LCO production, and early nodulation of soybean. We found that 1.57 mmol ammonium nitrate x L(-1) resulted in less rhizobial growth and rhizobial capacity to produce LCOs (on a per cell basis) than did 0.4 g yeast extract x L(-1), which contained the same amount of N as the ammonium nitrate. Increasing yeast extract to 0.8 g x L(-1) increased rhizobial growth and LCO production on a volume basis (per litre of culture) and did not affect cell capacity to produce LCOs; however, at 1.4 g yeast extract x L(-1) per cell, production was reduced. A mixture of 0.8 g yeast extract x L(-1) and 1.6 g casein hydrolysate x L(-1) resulted in the greatest bacterial growth and LCO production on a volume basis but reduced LCO production per cell. Changes in organic N level and source increased production of some of the measured LCOs more than others. LCO production was positively correlated with cell density when expressed on a volume basis; however, it was negatively correlated on a per cell basis. We conclude that although quorum sensing affected Nod factor production, increased levels of organic N, and specific compositions of organic N, increased LCO production on a volume basis. Greenhouse inoculation experiments showed that the medium did not modify nodule number and N fixation in soybean, suggesting that it could have utility in inoculant production.
authors.affiliation: Department of Plant Science, McGill University, Macdonald Campus, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Supanjani
authors.forename: Kyung D
authors.initials: KD
authors.lastname: Lee
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Almaraz
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Zhou
authors.forename: Donald L
authors.initials: DL
authors.lastname: Smith
mesh_terms: D020369:Bradyrhizobium / Q000254:growth & development*; D002364:Caseins / Q000378:metabolism; D007887:Fabaceae; D008070:Lipopolysaccharides / Q000096:biosynthesis*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000502:physiology*; D013025:Glycine max / Q000378:metabolism* / Q000382:microbiology; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013559:Symbiosis; D015003:Yeasts / Q000378:metabolism
chemical_list: D002364:Caseins; D008070:Lipopolysaccharides; D009566:Nitrates; C023023:lipid-linked oligosaccharides; C475729:casein hydrolysate; D009584:Nitrogen; C006568:ammonium nitrate