title: Tryptophan, thiamine and indole-3-acetic acid exchange between Chlorella sorokiniana and the plant growth-promoting bacterium Azospirillum brasilense.
abstract: During synthetic mutualistic interactions between the microalga Chlorella sorokiniana and the plant growth-promoting bacterium (PGPB) Azospirillum brasilense, mutual exchange of resources involved in producing and releasing the phytohormone indole-3-acetic acid (IAA) by the bacterium, using tryptophan and thiamine released by the microalga, were measured. Although increased activities of tryptophan synthase in C. sorokiniana and indole pyruvate decarboxylase (IPDC) in A. brasilense were observed, we could not detect tryptophan or IAA in the culture medium when both organisms were co-immobilized. This indicates that no extra tryptophan or IAA is produced, apart from the quantities required to sustain the interaction. Over-expression of the ipdC gene occurs at different incubation times: after 48 h, when A. brasilense was immobilized alone and grown in exudates of C. sorokiniana and at 96 h, when A. brasilense was co-immobilized with the microalga. When A. brasilense was cultured in exudates of C. sorokiniana, increased expression of the ipdC gene, corresponding increase in activity of IPDC encoded by the ipdC gene, and increase in IAA production were measured during the first 48 h of incubation. IAA production and release by A. brasilense was found only when tryptophan and thiamine were present in a synthetic growth medium (SGM). The absence of thiamine in SGM yielded no detectable IAA. In summary, this study demonstrates that C. sorokiniana can exude sufficient tryptophan and thiamine to allow IAA production by a PGPB during their interaction. Thiamine is essential for IAA production by A. brasilense and these three metabolites are part of a communication between the two microorganisms.
authors.affiliation: Environmental Microbiology Group, The Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz 23096, Mexico.
authors.forename: Oskar A
authors.initials: OA
authors.lastname: Palacios
authors.affiliation: Molecular Biology of Plants Group, Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz, B.C.S. 23096, Mexico.
authors.forename: Gracia
authors.initials: G
authors.lastname: Gomez-Anduro
authors.affiliation: Environmental Microbiology Group, The Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz 23096, Mexico The Bashan Institute of Science, 1730 Post Oak Ct., AL 36830, USA Department of Entomology and Plant Pathology, Auburn University, 301 Funchess Hall, Auburn, AL 36849, USA.
authors.forename: Yoav
authors.initials: Y
authors.lastname: Bashan
authors.affiliation: Environmental Microbiology Group, The Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz 23096, Mexico The Bashan Institute of Science, 1730 Post Oak Ct., AL 36830, USA Department of Entomology and Plant Pathology, Auburn University, 301 Funchess Hall, Auburn, AL 36849, USA legonzal04@cibnor.mx.
authors.forename: Luz E
authors.initials: LE
authors.lastname: de-Bashan
mesh_terms: D015806:Azospirillum brasilense / Q000378:metabolism*; D002262:Carboxy-Lyases / Q000235:genetics / Q000378:metabolism; D002708:Chlorella / Q000378:metabolism*; D003470:Culture Media / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D063245:Plant Development; D013559:Symbiosis / Q000502:physiology*; D013831:Thiamine / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism*; D014367:Tryptophan Synthase / Q000235:genetics / Q000378:metabolism
chemical_list: D003470:Culture Media; D007210:Indoleacetic Acids; C030737:indoleacetic acid; D014364:Tryptophan; C068832:indolepyruvate decarboxylase; D002262:Carboxy-Lyases; D014367:Tryptophan Synthase; D013831:Thiamine
keywords: Azospirillum; Chlorella; indole-3-acetic acid; mutualism; signaling; tryptophan