We propose to study PDRs and dust in 5 low-metallicity regions: N159 and
N214  in the LMC, N 27 in the SMC, and IC 10-SE in IC 10 using ISOCAM, ISOPHOT,
and the LWS. The low-metallicity interstellar medium will have profoundly
different properties than its higher metallicity counterpart in the Milky Way.
Decreased dust shielding will produce larger photodissociation regions, because
UV fields will penetrate much more deeply into the molecular clouds. The more
intense UV fields will likely destroy the smaller dust grains, which will have
important consequences on the shielding and the thermal balance in the
metal-poor ISM.
With the observations here proposed we will be able to: (1) determine the very
small grain spatial distribution and temperature and their contribution to the
heating-cooling balance, (2) determine the "classical" large grain spatial
distribution and temperature and consequently the UV radiation shielding
experienced by the gas phase of the ISM, (3) determine the emissivity index
of the large grains, which will contain information about their size
distribution and composition, (4) obtain an important set of FIR spectroscopic
PDR diagnostics, in particular the 158 um [C II] and the 145 um and 63 um
[O I] lines,  and, (5) in conjunction with our submm [C I] and CO
observations with the AST/RO telescope and existing KAO [C II] maps,
we will obtain for the first time a complete set of PDR diagnostics for
a number of low-metallicity systems as inputs and tests of PDR models.