Part 1: A single-ascending dose (SAD) study conducted in an inpatient setting over 6 days in healthy volunteer male and female subjects evaluated in up to 7 dose cohorts to identify the maximum tolerated dose (MTD) within the single dose range studied; and Part 2: A multiple-ascending dose (MAD) study conducted in an inpatient setting over 22 days in healthy volunteer male and female subjects evaluated in up to 4 dose cohorts that were proven tolerable in the SAD part of the study to identify the MTD of SYNB1020 within the multiple-dose range studied. Up to 48 subjects may be enrolled in this part of the study.