Metagenomics reveals a phylogenetically informed microbial signature associated with Morgellons disease

1. Problem Statement

Morgellons disease is a controversial condition characterized by cutaneous lesions that appear to extrude fibers, accompanied by systemic symptoms like fatigue, pain, and cognitive dysfunction. The prevailing medical consensus classifies it as a psychosomatic disorder (delusional parasitosis), as traditional diagnostic methods have failed to identify known pathogens. While some studies have suggested links to Borrelia burgdorferi (Lyme disease) or other tick-borne pathogens, these findings remain inconclusive. There has been a significant lack of deep, unbiased metagenomic exploration to determine if a novel or poorly characterized microbial etiology exists.

2. Methodology

The study employed a deep metagenomic sequencing approach on a family cohort of five individuals (Subjects 100–104), all exhibiting Morgellons-like skin lesions. Two subjects (100 and 104) reported significant systemic symptoms.

• Sample Collection: Two types of samples were collected from each subject:
  • Postauricular swabs (Type B): Serving as unaffected skin controls.
  • Lesion samples (Type A): Pooled fibrous lesions collected simultaneously.
• Sequencing: DNA was extracted using the QIAGEN DNeasy PowerSoil Pro Kit. Libraries were prepared and sequenced on the Element AVITI platform (2x150 bp), generating high-depth libraries (mean ~65.7 million reads per sample).
• Bioinformatics Pipeline:
  • Preprocessing: Human reads were depleted using Bowtie2 against GRCh38.p14. Reads were trimmed (AdapterRemoval) and quality-filtered (Phred >30).
  • Taxonomic Profiling: Kraken2 (PlusPF database) was used for initial microbial community characterization.
  • Assembly & Binning: De novo assembly was performed using MEGAHIT. Metagenome-Assembled Genomes (MAGs) were generated using two binning algorithms: Semibin2 (deep learning-based) and MetaBAT2 (coverage/composition-based).
  • Quality Control: MAGs were assessed using CheckM2. High-quality MAGs were defined as >70% completeness and <10% contamination.
  • Functional Analysis: Open Reading Frames (ORFs) were predicted with Prodigal and aligned to the UniRef90 database using DIAMOND to assess functional homology.
  • Phylogenetics: Representative MAGs were clustered using dRep, and a phylogenetic tree was constructed using GTDB-TK and IQ-TREE.

3. Key Contributions

• First Deep Metagenomic Study: This is the first study to apply untargeted, deep metagenomic sequencing specifically to Morgellons lesions.
• Discovery of Novel Microbial Signatures: The study identifies a distinct microbial signature in lesions that is phylogenetically structured and taxonomically distinct from healthy skin.
• Evidence of Novel Biology: The findings suggest the presence of organisms with poorly annotated genomes and novel functions that are not well-represented in current reference databases.

4. Key Results

A. Library Properties and Read Mapping

• Unmapped Reads: Lesion samples contained a significantly higher fraction of unmapped reads (mean 61.4%) compared to postauricular controls (mean 34%), suggesting the presence of sequences absent from standard databases.
• Classification Confidence: Lesion samples had a lower proportion of reads classified at the species level (48.8% vs. 77.7%) and lower mean k-mer support for classified reads (55.2% vs. 76.6%), indicating lower similarity to known references.
• GC Content: Lesion libraries exhibited higher GC content (57.4%) compared to controls (48.6%).

B. Assembly and Functional Analysis

• Assembly Size: Lesion samples produced larger and more variable assembly spans (up to 303.8 Mb) compared to controls (max 27.8 Mb), indicating higher community complexity.
• Functional Homology: ORFs from lesion assemblies showed lower rates of hits to the UniRef90 database. When hits were found, they had significantly lower alignment bitscores (lower confidence) compared to controls. This implies the presence of proteins with novel or divergent functions.

C. Taxonomic and Phylogenetic Analysis

• MAG Recovery: The study assembled 429 MAGs total, with 345 from lesions and 84 from controls. High-quality MAGs (>70% completeness) were recovered from both, but lesion samples yielded more.
• Taxonomic Shift:
  • Controls: Dominated by Bacillota (Firmicutes) and Actinomycetota, consistent with healthy skin microbiomes.
  • Lesions: Enriched in Pseudomonadota (Proteobacteria) and Bacteroidota.
• Phylogenetic Structure: Hierarchical clustering of representative MAGs revealed that samples grouped distinctly by type (lesion vs. control). Crucially, the phylogenetic tree identified subtrees composed exclusively of genomes assembled from lesion samples. One specific subtree contained genomes found only in the lesions of symptomatic individuals.

5. Significance and Conclusion

The study provides compelling evidence that Morgellons disease is associated with a specific, phylogenetically structured microbial signature that differs fundamentally from the healthy skin microbiome. The presence of sequences that are poorly represented in databases, combined with the recovery of distinct MAGs exclusive to lesions (and specifically symptomatic cases), challenges the notion that the condition is purely psychosomatic.

The authors conclude that while the specific etiology remains to be fully characterized, the data strongly motivates further investigation into a potential microbial cause. Future research should focus on larger, diverse cohorts and integrate proteomic and host immune profiling to link these molecular patterns to clinical manifestations.