The bacteria that convert ammonia to nitrite (nitrosomonas) are the same for both fresh and saltwater. If memory serves, the ones that convert nitrite to nitrate may be different---nitrospira for fresh and nitrobacter for salt. Nitrospira is moderately salt tolerant.
None of those reproduce from spores, but they are in the air and do get around. There are other types of nitrifying bacteria that do reproduce from spores, but they are not the ones that do the double-conversion process in which we're interested.
Originally Posted by bethyMT
Hey, all that bacteria seems gross, but those things keep us alive.
Evolutionary biologist and mollusc-maven Steven J Gould says they comprise almost half of our dry body weight.