SEM and TEM observations of SE1457 ΔsaeRS and wild-type strain. (A) Biofilms of SE1457ΔsaeRS, SE1457, and SE1457saec after 24 h of growth on hydroxyapatite disks were observed by SEM. Arrows show the extracellular polymeric substances (EPSs) (10,000× magnification). (B) Planktonic cells of SE1457ΔsaeRS and SE1457 cultured for 24 h were observed by TEM. Cell-cell accumulations in SE1457ΔsaeRS are circled; arrow indicates the thread-like material linking neighboring cells. WT, SE1457; SAE, SE1457ΔsaeRS; SAEC, SE1457saec.