GLBRC Ultra-Filtered Milk Permeate Fermentation Community

HYPOTHESIZED: Genomic pathways and reactor abundance/product associations suggest heterogeneous lactose-fermenting roles among the six abundant Actinobacteriota MAGs. ACT2 is proposed to contribute succinic acid, while bifid-shunt potential supports lactic/acetic acid production in ATO3 and Bifidobacterium MAGs. Lactose permease plus beta-galactosidase were identified in ACT2, BIF2 and BIF11; ATO3 lactose use remains inferred despite no identified LacS homologue. The listed MAGs are the analyzed Actinobacteriota subset, not six experimentally verified producers of every product. Reactor sugar depletion and organic-acid accumulation were measured, but their allocation to these members is computational and correlative. LCO1 also has inferred direct lactose utilization, so this is not an exclusive Actinobacteriota function.

Participating Taxa: Olsenella_B sp. (MAG ATO3), Pauljensenia sp. (MAG ACT2), Bifidobacterium tibiigranuli (MAG BIF2), Bifidobacterium sp. (MAG BIF11), Olsenella_B sp900119625 (MAG ATO6), Bifidobacterium thermophilum (MAG BIF18)

Metabolites: lactose (CHEBI:17716 · MediaIngredientMech · CMMMech), acetic acid (CHEBI:15366 · MediaIngredientMech · CMMMech), succinic acid (CHEBI:30031 · MediaIngredientMech · CMMMech)

Evidence

• PMID:37324413 - PARTIAL (COMPUTATIONAL)
  "members of the Actinobacteriota phylum are important in the degradation of lactose, via the Leloir pathway and the bifid shunt, and the production of acetic, lactic, and succinic acids "

HYPOTHESIZED: Reverse-beta-oxidation genes, EtfB phylogeny/gene neighborhoods and reactor profiles suggest different chain-elongating roles for the three abundant Firmicute MAGs. CLOS1 is proposed to use lactate and predominantly produce butyrate; LCO1 is proposed to use lactose directly; ACID1 may use ethanol, but that assignment is inconclusive and other substrates remain possible. Butyric, hexanoic and octanoic acids were measured in reactor broth, not assigned to individual cells by flux experiments. No genomic diagnostic of terminal chain length was established. Neither all Firmicutes consuming lactate nor every member producing all three acids is demonstrated; C4 butyrate is distinguished from the C6/C8 medium-chain products.

Participating Taxa: Clostridium_B sp. (MAG CLOS1), Agathobacter rectalis (MAG LCO1), Acidaminococcus sp. (MAG ACID1)

Metabolites: ethanol (CHEBI:16236 · MediaIngredientMech · CMMMech), butyric acid (CHEBI:30772 · MediaIngredientMech · CMMMech), hexanoic acid (CHEBI:30776 · MediaIngredientMech · CMMMech), octanoic acid (CHEBI:28837 · MediaIngredientMech · CMMMech)

Evidence

• PMID:37324413 - PARTIAL (COMPUTATIONAL)
  "members of the Firmicutes phylum contribute to the chain-elongation-mediated production of butyric, hexanoic, and octanoic acids, with different microbes using either lactose, ethanol, or lactic acid as the growth substrate "

HYPOTHESIZED: The conceptual model proposes that lactate made by some lactose-fermenting Actinobacteriota can supply CLOS1 chain elongation. ATO3 and Bifidobacterium MAGs represent proposed donor candidates, not a measured set of donor-recipient transfers. CLOS1 contains the inferred LacT, electron-confurcating LDH and associated EtfAB machinery; the other two abundant Firmicutes have different proposed substrates. The study did not directly trace ATO3-to-CLOS1 carbon flow, establish product-removal feedback on upstream fermentation, determine lactate stereochemistry or show complete conversion of lactose into medium-chain fatty acids. The canonical labels retain their existing genus-level or ambiguous groundings rather than assert newly identified species. CROSS_FEEDING denotes the hypothesized transfer model. SYNTROPHY does not require obligacy in the local schema, but adds product-removal feedback that this study does not resolve.

Participating Taxa: Olsenella_B sp. (MAG ATO3), Bifidobacterium tibiigranuli (MAG BIF2), Bifidobacterium sp. (MAG BIF11), Bifidobacterium thermophilum (MAG BIF18), Clostridium_B sp. (MAG CLOS1)

Evidence

• PMID:37324413 - PARTIAL (COMPUTATIONAL)
  "members of the Actinobacteriota phylum are important in the degradation of lactose, via the Leloir pathway and the bifid shunt, and the production of acetic, lactic, and succinic acids "
• PMID:37324413 - PARTIAL (COMPUTATIONAL)
  "The inferred connection between some Actinobacteriota fermenting lactose to lactic acid and some Firmicutes utilizing lactic acid for chain elongation"