Exhibit 99.1

Synlogic DESIGNED FOR LIFE SYNB1618Phase1/2a Clinical Trial Topline Data from PKU Patient CohortsJuly 15th, 2019

SYNB1618 Potential to Address Unmet Need Across Patient Groups 360 mmol /L Uncontrolled Adults Partially Controlled Adults(Adults on Kuvanand/or low-Phe Diet) Pediatric Patients (controlled / partially controlled) (Pediatric patients on Kuvan and / or low-Phe diet Phe Natural protein Phe Phe Initial Focus

SYNB1618 Phase 1/2a Study Design Single Ascending Dose (SAD)6 cohorts, N = 24 Multiple Ascending Dose (MAD)- TID x 7 days4 cohorts, N = 32 Dose ID Single Dose (SD)N = 4 Multiple Dose (MD)TID x 7 daysN =10 Dose Confirm MTD Part 1: Healthy Volunteers Part 2: PKU Patients PKU Clinical Trial DesignRandomized, double-blind placebo-controlled study at multiple sites in the US Primary outcome: establish safety/tolerability following single and multiple doses in HV and PKU patients Secondary outcome: SYNB1618 kinetics in fecesExploratory: change from baseline in plasma and urinary biomarkers of Phe metabolism Presented in September 2018 New Data

SYNB1618 Activity Biomarkers Indicate Significant Phe Consumption Similar activity in HVs and PKU Patients

Modeling: Potential For Phe Reduction in PKU Patients % Blood Phe lowering 7x1010 1x1011 3x1011 5x1011 125100755025 TPP >30% SYNB1618 Dose (CFU) 8-18% 11-26% 34-79% 57-131% Ranges representLow: PAL mechanism only (conservative) High: PAL + LAAD activity (estimates maximum with both pathways)

Upcoming Milestones and Path Forward Established new solid formulation and manufacturing process Completed EPO1 interactions with FDA to align on program plans (clinical, manufacturing, toxicology) Completed Phase 1/2a study (healthy volunteers and PKU patients)Initiate bridging study with solid formulation in Q3 2019Phase 2 study in PKU patients to assess Phe lowering to start in 1H 2020