FORM 4 [ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      
1. Name and Address of Reporting Person * Heffernan Michael Thomas 2. Issuer Name and Ticker or Trading Symbol SYNLOGIC, INC. [ SYBX ] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable)__X__ Director                    _____ 10% Owner
_____ Officer (give title below)    _____ Other (specify below)
(Last)         (First)         (Middle)
C/O SYNLOGIC, INC., 301 BINNEY STREET, SUITE 402
3. Date of Earliest Transaction (MM/DD/YYYY)
12/8/2020
(Street)
CAMBRIDGE, MA 02142
(City)       (State)       (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)
 
6. Individual or Joint/Group Filing (Check Applicable Line) _X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
6. Date Exercisable and Expiration Date 7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (right to buy)  $2.29  12/8/2020    A     30000       (1) 12/8/2030  Common Stock  30000  $0.00  30000  D   

Explanation of Responses:
(1)  The option vests and becomes exercisable in substantially equal installments on each of the first three anniversaries of the Transaction Date, subject to the Reporting Person continuing to provide services to the Issuer through such vesting date.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
Heffernan Michael Thomas
C/O SYNLOGIC, INC.
301 BINNEY STREET, SUITE 402
CAMBRIDGE, MA 02142
X



Signatures
/s/ Michael Heffernan 12/9/2020
**Signature of Reporting Person Date