  Given an ultragraph in the sense of Tomforde, we construct a topological
quiver in the sense of Muhly and Tomforde in such a way that the universal
C*-algebras associated to the two objects coincide. We apply results of Muhly
and Tomforde for topological quiver algebras and of Katsura for topological
graph C*-algebras to study the K-theory and gauge-invariant ideal structure of
ultragraph C*-algebras.
