  We calculate the strange quark content of the nucleon in 2+1-flavor lattice
QCD. Chirally symmetric overlap fermion formulation is used to avoid the
contamination from up and down quark contents due to an operator mixing between
strange and light scalar operators, \bar{s}s and \bar{u}u+\bar{d}d. At a
lattice spacing a=0.112(1) fm, we perform calculations at four values of
degenerate up and down quark masses, which cover a range of the pion mass M_pi
\simeq 300-540 MeV. We employ two different methods: one is a direct method
where we calculate the strange quark content by directly inserting the strange
scalar operator. The other is an indirect method where the quark content is
extracted from a derivative of the nucleon mass in terms of the strange quark
mass. With these two methods we obtain consistent results with each other. Our
best estimate f_{T_s}=0.009(15)(16) is in good agreement with our previous
studies in two-flavor QCD.
