nitrous bacteria vs eubacterium

nitrous bacteria and eubacterium both are nouns.

Word	Noun	Adjective	Verb	Adverb
nitrous bacteria	Yes	No	No	No
eubacterium	Yes	No	No	No

As nouns, eubacterium is a hypernym of nitrous bacteria; that is, eubacterium is a word with a broader meaning than nitrous bacteria:

nitrous bacteria: soil bacteria that oxidize ammonia to nitrites
eubacterium: a large group of bacteria having rigid cell walls; motile types have flagella

Other hypernyms of nitrous bacteria include eubacteria, true bacteria.

nitrous bacteria (noun)	eubacterium (noun)
soil bacteria that oxidize ammonia to nitrites	a large group of bacteria having rigid cell walls; motile types have flagella