a, Schematic of an SFB filament highlighting stages of its growth and differentiation. Gram stain of SFB after 4 days of growth on b, TC7s incubated at the indicated condition, and c, TC7s grown on TWs in low oxygen. Analysis of SFB grown on mICcl2 cells (d-g) and TC7s (h) on TWs at 1-2.5% O2: d, qPCR quantitation; e, length of individual SFBs; f, Gram stain; and g, Segment length analysis of representative 2-day old SFB filaments. h, SEM of SFB after 4 days of growth.