MSC-1 Dominant Core

Chitin-selected MSC-1 retained a broadly similar composition across prolonged passaging and storage-revival cycles, with residual drift rather than invariant membership. The selected consortium had 31 detected bacterial OTUs in Table 1 and Results, with its top 13 accounting for over 98% of reads; other source passages say approximately 35. The nine canonical participants represent an incomplete roster, not a defined nine-strain mixture. HYPOTHESIZED - repeated co-enrichment could reflect metabolic codependencies, but persistence and selection on chitin/soil-extract agar do not demonstrate obligate dependence, niche partitioning or measured chitin turnover.

Participating Taxa: Rhodococcus sp., Streptomyces sp., Dyadobacter sp., Taibaiella sp., Bosea sp., Sphingopyxis sp., Ensifer sp., Variovorax sp., Mycobacterium sp.

Metabolites: chitin (CHEBI:17029 · MediaIngredientMech · CMMMech)

Evidence

• PMID:32983014 - SUPPORT (IN_VITRO)
  "This consortium was re-designated: Model Soil Consortium – 1 (MSC-1)."
• PMID:32983014 - PARTIAL (IN_VITRO)
  "Because these species were co-enriched together over a 22-week period and through two rounds of freezing and revival, we hypothesized that there existed metabolic co-dependencies within MSC-1."

Pairwise isolates in M9 with 10 mM soluble N-acetylglucosamine (NAG) showed higher early-exponential optical density than the expected average of the two corresponding monocultures (p < 0.01 for reported positive comparisons). Named examples include Streptomyces-Rhodococcus, Streptomyces-Variovorax, Rhizobium-Rhodococcus and Ensifer-Rhodococcus. The difference was not significant in late exponential phase. Total OD does not resolve each partner biomass, reciprocal benefit or obligate syntrophy, and these NAG assays do not measure chitin-polymer degradation. The four canonical participants are a partial set of the named positive pairs; the source Rhizobium isolate is not canonically resolved here, and V4 does not distinguish which Ensifer OTU matches the isolate.

Participating Taxa: Rhodococcus sp., Streptomyces sp., Ensifer sp., Variovorax sp.

Metabolites: N-acetyl-D-glucosamine (CHEBI:28009 · MediaIngredientMech · CMMMech)

Evidence

• PMID:32983014 - SUPPORT (IN_VITRO)
  "Several of the combinations showed much higher growth than would be predicted including Streptomyces paired with Rhodococcus, Streptomyces paired with Variovorax, and Rhizobium paired with Rhodococcus."
• PMID:32983014 - SUPPORT (IN_VITRO)
  "observed Ensifer and Rhodococcus co-culture ODs were higher than predicted suggesting positive interactions"

A Pearson network pooled normalized relative 16S abundances across soil-incubation conditions, replicate samples and time points. Rhodococcus, Mycobacterium and Rhizobiales-associated OTUs had high betweenness centrality. Rhizobiales is an order, not a genus or a verified isolate identity. The two explicit canonical participants identify the named Rhodococcus and Mycobacterium subset, not every hub. Positive and negative co-abundance associations can reflect common environmental or temporal responses; they do not establish pairwise facilitation, competition, niche partitioning or keystone necessity. Soil chitin and liquid NAG assays are distinct contexts, and their partly matching correlation signs do not establish a shared mechanism.

Participating Taxa: Rhodococcus sp., Mycobacterium sp.

Evidence

• PMID:32983014 - SUPPORT (COMPUTATIONAL)
  "Rhodococcus had several positive and negative correlations with other genera of MSC-1, including Streptomyces, Variovorax, and Delftia (negative) and Rhizobiales (positive)."
• PMID:32983014 - SUPPORT (COMPUTATIONAL)
  "species of the Rhodococcus, Mycobacterium and Rhizobiales genera occupied positions of high centrality in the network"