Thanks Matthias, that is good to know.  From what I can tell from the properties being loaded in the static initializer, I can define:

index.solr=com.thinkaurelius.titan.diskstorage.solr.SolrIndex

That adds the shorthand "solr" to the registered index providers.  Then with that class and its dependencies on the classpath, I should be good to go? I can then define:

storage.index.search.backend=solr

And then when I do something like:

graph.makeKey('symbol').dataType(String.class).indexed('search', Vertex.class).make()

I'll then be working with Solr?

Thanks,

Jeff