  We show that the Malcev Lie algebra of the fundamental group of a compact
$2n+1$-dimensional Sasakian manifold with $n\ge 2$ admits a quadratic
presentation by using Morgan's bigradings of minimal models of mixed-Hodge
diagrams. By using bigradings of minimal models, we also simplify the proof of
the result of Cappelletti-Montano, De Nicola, Marrero and Yudin on Sasakian
nilmanifolds.
