What kind of bacteria live on the nodules on the roots to plants fixing atmospheric nitrogen, making it available for their own metabolic activities?

I think the name of the bacteria you are looking for here
is rhizobia. Rhizobia live in the soil and
convert nitrogen. They live in the root nodules of legumes. The legume plant and the
rhizobia live in harmony and help each other out. The
rhizobia has an enzyme system that reduces the amount of nitrogen
to the plant and in return the plant furnishes all of the nutrients that the bacteria
needs.

The rhizobia is only able to
fix the nitrogen in the soil if it is fixated to the legume. They are able to survive as
a free living organism but in this way they cannot convert nitrogen. When they are free
living they feed on other dead organisms.