Model Lignocellulose Formaldehyde Cross-Feeding Community

P. putida growing on vanillic acid accumulates approximately 0.6-0.8 mM formaldehyde, above the 0.5 mM concentration that prevents C. fimi growth in separate tolerance assays. This demonstrates toxic potential, not that the transient formaldehyde pulse is the dominant cause of coculture inhibition: P. putida also inhibits C. fimi on protocatechuic acid without formaldehyde generation.

Source Taxon: Pseudomonas putida

Target Taxon: Cellulomonas fimi

Metabolites: formaldehyde (CHEBI:16842 · MediaIngredientMech · CMMMech)

Biological Processes:

• interspecies interaction between organisms (GO:0044419 · PathwayMech)

Evidence

• doi:10.3390/microorganisms9020321 - SUPPORT (IN_VITRO)
  "formaldehyde produced by P. putida growing on vanillic acid"
• doi:10.3390/microorganisms9020321 - SUPPORT (IN_VITRO)
  "exceed the minimum inhibitory concentration for C. fimi"

M. extorquens addition lowers measurable formaldehyde produced by P. putida. PARTIAL - C. fimi is a potential beneficiary of reduced toxin exposure, but detoxification does not completely ameliorate its growth inhibition; other interactions dominate the tested batch conditions. Neither neutral fitness of the methylotroph nor full recipient rescue is established by the concentration change.

Source Taxon: Methylorubrum extorquens

Target Taxon: Cellulomonas fimi

Metabolites: formaldehyde (CHEBI:16842 · MediaIngredientMech · CMMMech)

Evidence

• doi:10.3390/microorganisms9020321 - SUPPORT (IN_VITRO)
  "presence of M. extorquens lowers those concentrations"
• doi:10.3390/microorganisms9020321 - SUPPORT (IN_VITRO)
  "M. extorquens was not able to completely ameliorate either the formaldehyde production or the growth inhibition."

Selected methionine-overproducing M. extorquens CM4744 supports C. fimi without supplied methionine, but only when methanol or succinate supports the producer; wild-type M. extorquens does not provide this rescue. The listed source-to-target direction denotes this methionine supply. Separately, C. fimi supports M. extorquens growth without an added methylotroph carbon substrate, consistent with reverse-direction carbon cross-feeding whose carrier was not resolved here. PARTIAL - These positive assays do not demonstrate autonomous reciprocal methionine-for-carbon codependence in one unsupplemented condition.

Source Taxon: Methylorubrum extorquens

Target Taxon: Cellulomonas fimi

Metabolites: methionine (CHEBI:16811 · MediaIngredientMech · CMMMech)

Biological Processes:

• interspecies interaction between organisms (GO:0044419 · PathwayMech)

Evidence

• doi:10.3390/microorganisms9020321 - PARTIAL (IN_VITRO)
  "mutualistic interaction between C. fimi and M. extorquens through metabolite exchange"
• doi:10.3390/microorganisms9020321 - SUPPORT (IN_VITRO)
  "M. extorquens to support C. fimi through the production of methionine"
• doi:10.3390/microorganisms9020321 - SUPPORT (IN_VITRO)
  "wild-type M. extorquens did not promote C. fimi growth."

PARTIAL - P. putida suppresses C. fimi growth and cellobiose consumption even on formaldehyde-free protocatechuic acid. Iron and vitamin/amino-acid supplementation improves coculture growth, consistent with competition for iron or methionine and other supplements. Spent medium lowers yield, but depletion and a secreted inhibitor remain alternatives; high iron itself inhibits C. fimi. These experiments do not establish a single exclusive inhibitory resource or competition causing methionine overproduction.

Biological Processes:

• interspecies interaction between organisms (GO:0044419 · PathwayMech)

Evidence

• doi:10.3390/microorganisms9020321 - PARTIAL (IN_VITRO)
  "resource competition"
• doi:10.3390/microorganisms9020321 - PARTIAL (IN_VITRO)
  "This could indicate either the effect of a soluble compound produced by P. putida, or the depletion by P. putida of important medium components, or both."