Cite Marinobacter HP15 genome paper for diatom-aggregation evidence (#55)

The HP15 type-strain genome paper (doi:10.4056/sigs.922139, Gärdes
et al. 2010, Stand Genomic Sci) directly describes HP15's specific
attachment to diatom cells and in vitro aggregation of algal cells
into marine snow particles. This is a perfect fit for the
Bacteria-Dependent Diatom Aggregation interaction in the existing
Thalassiosira-Marinobacter coculture community: it complements the
two PMID:20827289 evidence items with an orthogonal source that
characterizes HP15 itself rather than the aggregation assay.

The cached abstract for this paper was previously an orphan
references_cache file (committed alongside the literature-fetcher
PMC fallback infrastructure but not referenced by any community).
This wires it up to actual curated evidence.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: realmarcin

kb/communities/Thalassiosira_Marinobacter_Marine_Snow_Coculture.yaml

@@ -126,6 +126,14 @@ ecological_interactions:
     evidence_source: IN_VITRO
     snippet: T. weissflogii did not aggregate in axenic culture
     explanation: Supports the contrast between axenic diatom controls and bacteria-containing treatments.
+  - reference: doi:10.4056/sigs.922139
+    supports: SUPPORT
+    evidence_source: IN_VITRO
+    snippet: it showed specific attachment to diatom cells. In vitro it led to exopolymer
+      formation and aggregation of these algal cells to form marine snow particles
+    explanation: HP15 type-strain genome paper directly describes HP15's diatom-cell
+      attachment and resulting exopolymer-mediated aggregation into marine snow particles,
+      supporting the bacteria-dependent aggregation phenotype.
 - name: Transparent Exopolymer Particle Enhancement
   description: >
     M. adhaerens HP15 is linked to transparent exopolymeric particle formation