This is a 24-week study of intestinal microbiome transplant in people with ALS. All participants will be evaluated clinically in person for 4 visits. Blood and mailed/ fresh stool samples will also be collected. Blood samples will be used to determine changes in neurofilament light chain over time. Stool samples will be processed for microbiome analysis. Participants will have phone visits to further evaluate safety and tolerability. They will then undergo antibiotic conditioning and a standard bowel preparation before being assigned to the investigational product, MTP-101C .

This is a 24-week Phase I/II study of MTT in people with Amyotrophic Lateral Sclerosis. All participants will be evaluated clinically in person at weeks 0, 4, 12, and 24 visits. Blood and mailed/ fresh stool samples will be collected at weeks 0, 4, 8, 12, and 24. Blood samples will be used to determine changes in neurofilament light chain over time. Stool samples from weeks 0, 4,8, 12, and 24 will be processed by molecular methods (metagenomics and metatranscriptomics) for microbiome analysis. Participants will also have phone visits at weeks 1, 8, 16, and 20, which will be used to further evaluate safety and tolerability and the ALSFRS-R score.

Participants will first undergo antibiotic conditioning with oral vancomycin 250 mg twice daily for 10 days. Neomycin 500 mg twice daily will be added to the last 3 days of vancomycin. This will be followed by ingestion of a standard bowel preparation with magnesium citrate. Participants will then ingest 2 capsules of MTP-101C daily for 3 days, then 1 capsule of MTP-101C daily for 8 weeks.

All participants will be assigned to the investigational product.

Inclusion Criteria:

• Diagnosis of ALS according to Gold Coast Criteria
• Age: 18+ years at enrollment
• Fast-progressing (ALSFRS-R change of at least 1.5 points per month between last 2 measurements at screening)
• Modestly but not severely affected (ALSFRS-R score at or above 24 at screening)
• Able to swallow capsules and expected to be able to for the duration of the trial (ALSFRS-R "swallowing" score of 3 or 4 at screening)
• Expected to survive for the duration of the trial
• Taking any combination of riluzole, edaravone, and/or tofersen at a stable dose for 30 days prior to screening, or not taking any of these and not expected to during the study.
• Capable of giving written consent.
• If sexually active, must agree to use contraceptive or abstinence for duration of treatment.
• Females of child-bearing age must have negative pregnancy test at screening.

Exclusion Criteria:

• Concurrent illness or laboratory abnormalities that could confound the measurement of ALS progression or the microbiome or interfere with the ability to complete the study.
• Taking probiotics, nutraceuticals, or herbal remedies within 2 weeks of screening
• Taking antibiotics within 3 months of screening.
• Taking any investigational study drug within 30 days of screening or five half-lives of the prior agent.
• Previous exposure to MTT.
• Pregnancy.
• Known specific food allergy with anaphylaxis
• Other co-morbid conditions that, in the opinion of the study investigator, place the participant at increased risk of complications, interfere with study participation or compliance, or confound study objectives.