Zn(2+) uptake systems are required for many enteric pathogens to survive and form biofilm in zinc-deficient conditions. ykgM and zinT (formerly yodA), regulated by Zur (zinc uptake regulator), have been reported as being highly induced during zinc shortage. This work reports that ykgM and zinT in enterohemorrhagic Escherichia coli (EHEC) O157:H7 biofilms under fluidic conditions were highly expressed compared to those in stationary-phase planktonic cells and a mutation of either ykgM or zinT genes led to the inhibition of curli biosynthesis. Inductively coupled plasma mass spectroscopy showed that the ykgM and zinT mutants contained lower concentrations of Zn(2+) than the wild type. Both mutants were less attached to both the glass surface of a microchannel and epithelial cells than the wild type. Quantitative reverse-transcription PCR data indicated that the expression of csgA, which encodes the major curli subunit, was inhibited in both mutants with a zinc deficiency. Scanning electron microscopy showed that the mutants grown under zinc-deficient condition were covered with a lower amount of curli compared to the wild type and often became filamentous. Zn(2+) supplementation restored curli production and prevented filamentation in the mutants. Overall, under zinc-deficient conditions, YkgM and ZinT proteins are required for maintaining optimal zinc concentration in EHEC and intracellular zinc deficiency inhibits curli production.