Parachlorella kessleri + Saccharomyces cerevisiae Mutualistic Co-culture

HYPOTHESIZED - Reciprocal oxygen/carbon dioxide exchange is proposed for P. kessleri and S. cerevisiae. Results 3.2 of PMID42217804 attributes sustained algal growth after day 6 most likely to local yeast-derived CO2 enrichment. The inspected main-text methods do not directly measure reciprocal gas flux or isolate gas-exchange mediation. This is a mechanistic interpretation, not demonstrated bidirectional transfer or reciprocal fitness benefit. Separate supplements remain uninspected.

Source Taxon: Parachlorella kessleri

Target Taxon: Saccharomyces cerevisiae

Metabolites: oxygen (CHEBI:15379 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech)

Evidence

• PMID:42217804 - PARTIAL (OTHER)
  "Microalgae and yeasts can establish a mutualistic relationship based on reciprocal oxygen/carbon dioxide exchange, offering a strategy to overcome productivity limits caused by the slow growth of microalgae."
• PMID:42217804 - PARTIAL (IN_VITRO)
  "microalgal growth was sustained and boosted in co-culture, most likely due to the local CO2 enrichment of the medium provided by yeast activity, in addition to atmospheric CO2."

P. kessleri growth was maintained in coculture after the day 6 transition to phototrophy. Figure 3 compares BBM + NO3 monoculture, glucose/peptone-enriched BG10P10 monoculture and BG10P10 coculture: reported day-12 algal cell concentrations are 2.8-fold and 4.8-fold the BBM control in enriched monoculture and coculture, respectively. Thus yeast is associated with an additional growth benefit, but the full 4.8-fold comparison includes medium enrichment. Nutrient competition and gas exchange are proposed explanations of the relative lipid response, not isolated mediation estimates. The day-14 bulk Nile Red assay does not establish taxon-specific lipid production.

Source Taxon: Saccharomyces cerevisiae

Target Taxon: Parachlorella kessleri

Biological Processes:

• growth (GO:0040007 · PathwayMech)
• lipid metabolic process (GO:0006629 · PathwayMech)

Evidence

• PMID:42217804 - PARTIAL (IN_VITRO)
  "Yeast sustained microalgal growth during the transition to phototrophy after glucose depletion (day 6) and promoted lipid accumulation through nutrient competition."
• PMID:42217804 - SUPPORT (IN_VITRO)
  "The presence of glucose and peptone in BG10P10 medium brought higher cell concentrations, with a maximum at day 12 with a 2.8-fold higher concentration in BG10P10 condition and a 4.8-fold higher concentration in co-culture condition (Fig. 3A and B)."

HYPOTHESIZED - Yeast viability remained above 68% during approximately 8 days of nutrient limitation, which the authors interpret as possible metabolic support by microalgal EPS-derived molecules. AFM showed visible EPS and cell-surface changes, and FluidFM found stronger, longer cell interactions, likely associated with EPS. These positive viability and biophysical observations do not by themselves demonstrate EPS-carbon uptake, donor-to-recipient transfer or dependence of yeast survival on EPS.

Source Taxon: Parachlorella kessleri

Target Taxon: Saccharomyces cerevisiae

Metabolites: exopolysaccharide (CHEBI:72813 · MediaIngredientMech · CMMMech)

Evidence

• PMID:42217804 - PARTIAL (IN_VITRO)
  "yeast viability remained above 68%, indicating possible metabolic support from microalgae via exopolysaccharides (EPS) - derived molecules"

Two distinct positive endpoints are reported for the P. kessleri-S. cerevisiae coculture. Figure 3 measures P. kessleri cell concentration: at day 12, BG10P10 coculture is reported as 4.8-fold the BBM + NO3 monoculture control, while BG10P10 algal monoculture is 2.8-fold that control. This is not a fourfold isolated yeast effect or a dry-biomass measurement. Separately, Methods 2.3 assays day-14 pellets resuspended at 1.0 x 10^8 cells/mL using bulk Nile Red fluorescence. Results 3.2 reports 3437 +/- 17 a.u. for BBM control and 14195 +/- 216 a.u. for coculture, and calls the latter 4.3-fold; the ratio of those means is approximately 4.13. Methods specifies 2 micrograms/mL dye, whereas Results specifies 2.5. These reporting conflicts remain unresolved. No species separation is described for this lipid assay in the inspected main text; relative signal is not lipid mass, volumetric productivity, or proof of exclusively algal lipid production. The combined endpoint remains community-level to preserve that mixed-assay boundary.

Biological Processes:

• growth (GO:0040007 · PathwayMech)
• lipid metabolic process (GO:0006629 · PathwayMech)

Evidence

• PMID:42217804 - SUPPORT (IN_VITRO)
  "The presence of glucose and peptone in BG10P10 medium brought higher cell concentrations, with a maximum at day 12 with a 2.8-fold higher concentration in BG10P10 condition and a 4.8-fold higher concentration in co-culture condition (Fig. 3A and B)."
• PMID:42217804 - SUPPORT (IN_VITRO)
  "to enable species differentiation, precise cell quantification and to measure cell population viability."
• PMID:42217804 - SUPPORT (IN_VITRO)
  "Relative lipid levels were then measured using Nile Red staining coupled with fluorescence spectroscopy (Rumin et al., 2015)."
• PMID:42217804 - SUPPORT (IN_VITRO)
  "Pellets were thawed immediately before analysis and resuspended in deionized water to a final concentration of 1.0 × 108 cells/mL."
• PMID:42217804 - SUPPORT (IN_VITRO)
  "3437 ± 17 a. u., and in co-culture conditions with a lipid content increased to 14195 ± 216 a. u.."
• PMID:42217804 - SUPPORT (IN_VITRO)
  "the co-culture exhibited a relative lipid content 4.3-fold higher than that observed in BBM + NO3."
• PMID:42217804 - SUPPORT (IN_VITRO)
  "concentration of 2 µg/mL in 40% (v/v) dimethyl sulfoxide (DMSO)"
• PMID:42217804 - SUPPORT (IN_VITRO)
  "a Nile red concentration of 2.5 µg/mL was selected for the comparison."