[ii]{}\], \[N [ii]{}\], and \[C [ii]{}\] line intensities. The \[O [iii]{}\] 88 $\mu$m line intensity is not fully reproduced by our model, hinting towards the possible presence of yet another low-density high-ionisation medium. The \[O [i]{}\] emission is consistent with a dense PDR of low covering factor, and we find no evidence for an X-ray dominated component. The PDR component accounts for only 10% of the \[C [ii]{}\] emission. Magnetic fields, known to be strong in star-forming regions, may dominate the pressure in the PDR. For example, for field strengths of the order of 100 $\mu$G, up to 50% of the \[C [ii]{}\] emission may come from the PDR. ]{}

Introduction
============

Star formation in the most pristine environments of the early universe is poorly understood. The closest analogs to chemically unevolved systems are the low metallicity dwarf galaxies of our local universe. But even those well-studied nearby galaxies continue to plague us with fundamental questions on what triggers and regulates star formation in metal-poor gas-rich conditions. Certainly, from an observational point of view, at all wavelengths, local universe low-metallicity dwarf galaxies show dramatic differences compared to their more metal-rich counterparts [@kunth-2000 for a review], in the mid-infrared (MIR), far-infrared 