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Massive stars likely played an important role in the reionization of theUniverse, and the formation of the first black holes. Massive stars inlow-metallicity environments in the local Universe are reminiscent of theirhigh redshift counterparts. In a previous paper, we reported on indicationsthat the stellar winds of low-metallicity O stars may be stronger thanpredicted, which would challenge the current paradigm of massive starevolution. In this paper, we aim to extend our initial sample of six O stars inlow-metallicity environments by four. We aim to derive their stellar and windparameters, and compare these to radiation-driven wind theory and stellarevolution models. We have obtained intermediate-resolution VLT/X-Shooterspectra of our sample of stars. We derive the stellar parameters by fittingsynthetic fastwind line profiles to the VLT/X-Shooter spectra using a geneticfitting algoritm. We compare our parameters to evolutionary tracks and obtainevolutionary masses and ages. We also investigate the effective temperatureversus spectral type calibration for SMC and lower metallicities. Finally, wereassess the wind momentum versus luminosity diagram. The derived parameters ofour target stars indicate stellar masses that reach values of up to 50$M_{\odot}$. The wind strengths of our stars are, on average, stronger thanpredicted from radiation-driven wind theory and reminiscent of stars with anLMC metallicity. We discuss indications that the iron content of the hostgalaxies is higher than originally thought and is instead SMC-like. We findthat the discrepancy with theory is lessened, but remains significant for thishigher metallicity. This may imply that our current understanding of the windproperties of massive stars, both in the local universe as well as at cosmicdistances, remains incomplete.

The properties of ten O-type stars in the low-metallicity galaxies IC 1613, WLM and NGC 3109