“…Methods to measure the impact of microbial interactions on growth or fitness require either knowledge of the absolute abundance of each member of the community separately, or relative abundance of each member multiplied by the absolute abundance of the community. In the first approach, a quantitatively measurable trait unique to each member is required, to measure each member abundance separately, e.g., colony morphology ( Traxler and Kolter, 2015 ), growth on selective media ( Cheong et al, 2021 ), fluorescent tag ( Conacher et al, 2020 ), specific enzymatic activity ( Rivett et al, 2016 ; Liu et al, 2020a ), specific DNA sequence ( Kumar et al, 2019 ; Blasche et al, 2021 ), or a physical separation allowing for individual quantification ( Liu et al, 2017 ; Moutinho et al, 2017 ; Jo et al, 2021 ). Physical separation is useful to study uncharacterized isolates; however, it precludes the detection of contact-dependent interactions.…”