Garrity, George M.; Bell, Julia A.; Lilburn, Timothy (2005), Brenner, Don J.; Krieg, Noel R.; Staley, James T. (eds.), "Class I. Alphaproteobacteria class. nov.", Bergey’s Manual® of Systematic Bacteriology: Volume Two The Proteobacteria Part C The Alpha-, Beta-, Delta-, and Epsilonproteobacteria, Boston, MA: Springer US, pp. 1–574, doi:10.1007/978-0-387-29298-4_1, ISBN978-0-387-29298-4, retrieved 2022-07-22
Myrold, David D. (2021-01-01), Gentry, Terry J.; Fuhrmann, Jeffry J.; Zuberer, David A. (eds.), "15 - Transformations of nitrogen", Principles and Applications of Soil Microbiology (Third Edition), Elsevier, pp. 385–421, ISBN978-0-12-820202-9, retrieved 2022-07-22
Pepper, Ian L.; Gerba, Charles P. (2015-01-01), Pepper, Ian L.; Gerba, Charles P.; Gentry, Terry J. (eds.), "Chapter 10 - Cultural Methods", Environmental Microbiology (Third Edition), San Diego: Academic Press, pp. 195–212, ISBN978-0-12-394626-3, retrieved 2022-07-22
Ward, B. B. (2013-01-01), "Nitrification☆", in Fath, Brian (ed.), Encyclopedia of Ecology (Second Edition), Oxford: Elsevier, pp. 351–358, ISBN978-0-444-64130-4, retrieved 2022-07-22