Chlorella-Azospirillum Synthetic Mutualism

C. sorokiniana UTEX 2714 and A. brasilense Cd show nutrient- and time-dependent population benefits in illuminated bead cultures. The initial 12-hour nutrient-rich, N-free or C-free treatment was followed by transfer to SGM. Mutualism is not uniform across comparisons: after the nutrient-rich start, later bacterial counts did not differ significantly from individually immobilized controls.

Source Taxon: Chlorella sorokiniana UTEX 2714

Target Taxon: Azospirillum brasilense Cd

Biological Processes:

• photosynthesis (GO:0015979 · PathwayMech)
• biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)

Evidence

• doi:10.1007/s00248-018-1282-1 - SUPPORT (IN_VITRO)
  "synthetic mutualism between C. sorokiniana and A. brasilense can be modulated"
• doi:10.1007/s00248-018-1282-1 - PARTIAL (IN_VITRO)
  "Overall, populations of bacteria and microalgae were larger when co-immobilized."

PARTIAL - algal exudates supported bacterial IAA production; supplementation required tryptophan plus thiamine diphosphate rather than tryptophan alone. This supports algal-resource use by Cd. Within co-immobilized cultures, bulk-medium tryptophan and IAA were undetected; enzyme and ipdC expression measurements support proposed local exchange but do not directly quantify its flux. IPDC activity alone is neither uniquely bacterial nor specific to IAA production.

Source Taxon: Chlorella sorokiniana UTEX 2714

Target Taxon: Azospirillum brasilense Cd

Metabolites: L-tryptophan (CHEBI:16828 · MediaIngredientMech · CMMMech), thiamine (CHEBI:18385 · MediaIngredientMech · CMMMech), indole-3-acetic acid (CHEBI:16411 · MediaIngredientMech · CMMMech)

Biological Processes:

• indole-3-acetic acid biosynthetic process (GO:0009684 · PathwayMech)
• tryptophan biosynthetic process (GO:0000162 · PathwayMech)
• biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)

Evidence

• doi:10.1093/femsec/fiw077 - PARTIAL (IN_VITRO)
  "using tryptophan and thiamine released by the microalga"
• doi:10.1007/s00248-018-1282-1 - PARTIAL (IN_VITRO)
  "production of signal molecules tryptophan and indole-3-acetic acid"

Co-immobilization experimentally places both members in alginate beads; mixed aggregates were observed with condition- and time-dependent patterns. N-free-start attachment weakened later, whereas large C-free-start clusters developed late. This is engineered proximity and observed organization, not demonstrated partner-mediated colonization facilitation.

Source Taxon: Azospirillum brasilense Cd

Target Taxon: Chlorella sorokiniana UTEX 2714

Biological Processes:

• cell aggregation (GO:0098743 · PathwayMech)
• biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)

Evidence

• doi:10.1007/s00248-018-1282-1 - SUPPORT (IN_VITRO)
  "Formation of aggregates made of microalgae and bacteria occurred"
• doi:10.1093/femsec/fiw077 - SUPPORT (IN_VITRO)
  "Microorganisms were immobilized individually and co-immobilized in alginate beads"

In dark, aerobic, glucose-fed assays with or without ammonium, Cd and Sp6 cocultures increased algal starch and AGPase activity. Synthetic IAA gave a transient response, and the Sp6-derived IAA-attenuated SpM7918 retained smaller starch effects. Most cocultures reduced algal population growth; starch is a physiological endpoint, not reciprocal fitness. The Cd tryptophan/IAA correlation under N starvation was nonsignificant, and the intracellular regulatory step remains unresolved.

Source Taxon: Azospirillum brasilense Cd

Target Taxon: Chlorella sorokiniana UTEX 2714

Metabolites: L-tryptophan (CHEBI:16828 · MediaIngredientMech · CMMMech), indole-3-acetic acid (CHEBI:16411 · MediaIngredientMech · CMMMech)

Biological Processes:

• indole-3-acetic acid biosynthetic process (GO:0009684 · PathwayMech)
• biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)

Evidence

• doi:10.1016/j.resmic.2016.02.005 - PARTIAL (IN_VITRO)
  "measured the relations between tryptophan production, the phytohormone indole-3-acetic acid"
• doi:10.1016/j.resmic.2016.02.005 - SUPPORT (IN_VITRO)
  "created by co-immobilization in alginate beads"