  The Wolf-Rayet (WR) nebula NGC3199 has been suggested to be a bow shock
around its central star WR18, presumably a runaway star, because optical images
of the nebula show a dominating arc of emission south-west of the star. We
present the XMM-Newton detection of extended X-ray emission from NGC3199,
unveiling the powerful effect of the fast wind from WR18. The X-ray emission is
brighter in the region south-east of the star and analysis of the spectral
properties of the X-ray emission reveals abundance variations: i) regions close
to the optical arc present nitrogen-rich gas enhanced by the stellar wind from
WR18 and ii) gas at the eastern region exhibits abundances close to those
reported for nebular abundances derived from optical studies, signature of an
efficient mixing of the nebular material with the stellar wind. The dominant
plasma temperature and electron density are estimated to be
$T\approx1.2\times$10$^{6}$ K and $n_\mathrm{e}$=0.3 cm$^{-3}$ with an X-ray
luminosity in the 0.3-3.0 keV energy range of
$L_\mathrm{X}$=2.6$\times$10$^{34}$ erg s$^{-1}$. Combined with information
derived from Herschel and the recent Gaia first data release, we conclude that
WR18 is not a runaway star and the formation, chemical variations, and shape of
NGC3199 depend on the initial configuration of the interstellar medium.
