title: Influence of tryptophan and indole-3-acetic acid on starch accumulation in the synthetic mutualistic Chlorella sorokiniana-Azospirillum brasilense system under heterotrophic conditions.
abstract: This study measured the relations between tryptophan production, the phytohormone indole-3-acetic acid (IAA) and the metabolism and accumulation of starch during synthetic mutualism between the microalgae Chlorella sorokiniana and the microalgae growth-promoting bacteria Azospirillum brasilense, created by co-immobilization in alginate beads. Experiments used two wild-type A. brasilense strains (Cd and Sp6) and an IAA-attenuated mutant (SpM7918) grown under nitrogen-replete and nitrogen-starved conditions tested under dark, heterotrophic and aerobic growth conditions. Under all incubating conditions, C. sorokiniana, but not A. brasilense, produced tryptophan. A significant correlation between IAA-production by A. brasilense and starch accumulation in C. sorokiniana was found, since the IAA-attenuated mutant was not producing increased starch levels. The highest ADP-glucose pyrophosphorylase (AGPase) activity, starch content and glucose uptake were found during the interaction of A. brasilense wild type strains with the microalgae. When the microalgae were grown alone, they produced only small amounts of starch. Supplementation with synthetic IAA to C. sorokiniana grown alone enhanced the above parameters, but only transiently. Activity of α-amylase decreased under nitrogen-replete conditions, but increased under nitrogen-starved conditions. In summary, this study demonstrated that, during synthetic mutualism, the exchange of tryptophan and IAA between the partners is a mechanism that governs several changes in starch metabolism of C. sorokiniana, yielding an increase in starch content.
authors.affiliation: Environmental Microbiology Group, Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz, B.C.S. 23096, Mexico.
authors.forename: Oskar A
authors.initials: OA
authors.lastname: Palacios
authors.affiliation: Environmental Microbiology Group, Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz, B.C.S. 23096, Mexico.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Choix
authors.affiliation: Environmental Microbiology Group, Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz, B.C.S. 23096, Mexico; The Bashan Institute of Science, 1730 Post Oak Court, Auburn, AL 36830, USA; Dept. of Entomology and Plant Pathology, 301 Funchess Hall, Auburn University, Auburn, AL 36849, USA.
authors.forename: Yoav
authors.initials: Y
authors.lastname: Bashan
authors.affiliation: Environmental Microbiology Group, Northwestern Center for Biological Research (CIBNOR), Av. IPN 195, La Paz, B.C.S. 23096, Mexico; The Bashan Institute of Science, 1730 Post Oak Court, Auburn, AL 36830, USA; Dept. of Entomology and Plant Pathology, 301 Funchess Hall, Auburn University, Auburn, AL 36849, USA. Electronic address: legonzal04@cibnor.mx.
authors.forename: Luz E
authors.initials: LE
authors.lastname: de-Bashan
mesh_terms: D000332:Aerobiosis; D015806:Azospirillum brasilense / Q000254:growth & development / Q000378:metabolism*; D002708:Chlorella / Q000254:growth & development / Q000378:metabolism*; D003624:Darkness; D052836:Heterotrophic Processes; D007210:Indoleacetic Acids / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D013213:Starch / Q000378:metabolism*; D013559:Symbiosis; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D007210:Indoleacetic Acids; C030737:indoleacetic acid; D014364:Tryptophan; D013213:Starch; D009584:Nitrogen
keywords: Azospirillum; Chlorella; Indole-3-acetic acid; Plant growth-promoting bacteria; Synthetic mutualism; Tryptophan