HMO mutualism graph: bound reciprocal exchange to tested strains, nutrient limitation and pH #1425

Ecoli_Bifidobacterium_bifidum_Infant_gut_HMO_Mutualism_Coculture.yaml, PMID:42020426.

Retain the experimentally supported reciprocal exchange: E. coli K12 and an infant B. bifidum isolate co-grew under cysteine/casamino-acid limitation; the delta-cysE control impaired growth and ethanol-killed controls did not sustain it. Bound claims to that in vitro system. Spent-medium sugar uptake required pH readjustment from 4.3 to 6.3, with fucose and galactose measured. Do not imply isotope-resolved cysteine export, demonstrated control of E. coli abundance in infants, or an experimentally quantified positive-feedback time course. Keep return-to-cysteine maintenance PARTIAL, and distinguish the existing mutualism summary from a separate downstream host endpoint. No additional causal structure needed.

Deduplication: 748 all-state issue titles/bodies and ignored/hidden-inclusive local review, research, history, tests, scripts and workflow files. Relevant #1264, #826, #827, #830, #365 and #442 read; no exact duplicate within that scope. Not every issue comment searched. Primary cached main-body texts reviewed, not visual figures, raw data or separate supplements.