  An active environment is a reservoir containing \emph{active} materials, such
as bacteria and Janus particles. Given the self-propelled motion of these
materials, powered by chemical energy, an active environment has unique,
nonequilibrium environmental noise. Recently, studies on engines that harvest
energy from active environments have attracted a great deal of attention
because the theoretical and experimental findings indicate that these engines
outperform conventional ones. Studies have explored the features of active
environments essential for outperformance, such as the non-Gaussian or
non-Markovian nature of the active noise. However, these features have not yet
been systematically investigated in a general setting. Therefore, we
systematically study the effects of the non-Gaussianity and non-Markovianity of
active noise on engine performance. We show that non-Gaussianity is irrelevant
to the performance of an engine driven by {any linear force (including a
harmonic trap) regardless of time dependency}, whereas non-Markovianity is
relevant. However, for a system driven by a general nonlinear force, both
non-Gaussianity and non-Markovianity enhance engine performance. Also, the
memory effect of an active reservoir should be considered when fabricating a
cyclic engine.
