Supporting Information S3 Experimental schematics. Supporting Information S2 engineered symbiotic biofilm. (DOC) (DOC) Supporting Information S4 aggregates and single cells. (DOC) Supporting Information S5 blue and yellow biomass. (DOC) Supporting Information S6 and treatment procedures. (DOC) Supporting Information S7 mass median. (DOC) Acknowledgments 40 mm cell strainer (BD Falcon, 352340) before the effluent was adjusted to 0.07 and 1 mL was inoculated into each fresh flow lane. The treated and untreated effluents were also plated in parallel with inoculation to confirm that they contained equal numbers of blue and yellow cells. Imaging and image processing Images of the biofilms were captured with a Zeiss 510 upright confocal laser scanning microscope (CLSM), controlled by Carl Zeiss AIM. A Zeiss Achroplan 406/0.8 W objective was used to capture all images, images were captured with 5126512 pixel resolution, and all image stacks were captured with identical pinhole and gain settings. eCFP excitation: 458 nm Argon laser, emission filter: BP 480–520 nm. eYFP excitation: 514 nm Argon laser, emission filter: LP 530 nm. All image-based measurements were calculated using the COM- STAT biofilm image processing package in Matlab [22]. At least three biological replicates were grown at a time for each condition, and every condition was repeated on at least two different days. Averages were taken of COMSTAT results from at least three randomly selected images, taken at a variety of locations within the flow lane. Additions to the COMSTAT software enabled calculations of biomass median, as detailed in Supporting Information S7 [22]. 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