Nitrospira moscoviensis

In 1995, Silke Ehrich discovered Nitrospira moscoviensis in a sample taken from an eroded iron pipe.[2] The pipe was a part of a heating system in Moscow, Russia.[2] The rust was transferred to a culture where cells could be isolated.[2] For optimum growth, Ehrich and his team cultivated the cells on a mineral salt medium at a temperature of 39 °C and at a pH of 7.6-8.0.[2]

Nitrospira moscoviensis is classified as being gram-negative, non-motile, and having a curved rod shape.[2] The curved rods are approximately 0.9-2.2 µm long x 0.2-0.4 µm wide.[2] N. moscoviensis can exist in both aquatic and terrestrial habitats and reproduces using binary fission.[2] Defining features of N. moscoviensis is the absence of intra-cytoplasmic membranes and carboxysomes possession of a flatulent periplasmic space.[5]

Nitrospira moscoviensis is a facultative lithoautotroph commonly referred to as a chemolithoautotroph.[2] In aerobic environments, N. moscoviensis obtains energy by oxidizing nitrite to nitrate.[5] Without the element molybdenum, the nitrite-oxidizing system will not function.[5] When N. moscoviensis is in nitrite free environments it can use aerobic hydrogen oxidation.[3] When N. moscoviensis reduces nitrite using hydrogen as an electron donor growth is blocked.[3] A key difference in N. moscoviensis’ nitrite-oxidizing system is location; unlike most nitrate oxidizing systems, it is not located in the cytoplasmic membrane.[5] Kirstein and Bock (1993) implied that the location of the nitrite-oxidizing system corresponds directly to N. moscoviensis having an enlarged periplasmic space.[6] By oxidizing nitrate outside of the cytoplasmic membrane, a permease nitrite system is not needed for the proton gradient.[5] The exocytoplasmic oxidation of nitrite also prevents build-up of toxic nitrite within the cytoplasm.[5] Another important metabolism ability for N. moscoviensis is its ability to cleave urea to ammonia and CO₂.[3] The ability to use urea comes directly from the presence of urease encoding genes which is interesting because most nitrite-oxidizing bacteria are unable to use ammonia as an energy source.[3] Urease encoding genes function by catalyzing urea hydrolysis to form ammonia and carbamate.[3]

Nitrospira moscoviensis grows in temperatures from 33 to 40 °C and pH 7.6-8.0 with an optimal nitrite concentration of 0.35 nM.[2] Nitrospira moscoviensis plays a key role in the two-step Nitrogen Cycle process.[3] The first step of Nitrification requires an ammonia-oxidizing bacterium (AOB) or ammonia-oxidizing archaeon (AOA) followed by a nitrite-oxidizing bacterium (NOB).[3] The unique capability of N. moscoviensis to cleave urea into ammonia and carbon dioxide allows for a symbiotic relationship with ammonia-oxidizing microorganisms (AOM) that lack this urease-production ability also known as negative AOM.[3] A correlation in environment preferences between Nitrospira species with nxrB gene encoding the β-subunit of nitro-oxidoreductase and AOM species with amoA gene further confirmed this relationship.[7] N. moscoviensis provides ammonia via hydrolysis of urea to these ammonia-oxidizing microorganisms which in turn produce nitrite, the primary energy source of N. moscoviensis.[3] The relationship between ureolytic nitrite-oxidizing bacteria and negative AOM is called reciprocal feeding.[3] Thus far, Nitrospira species have been recognized in natural environments as the primary vehicle for nitrite oxidation including soils, activated-sludge, ocean and fresh water, hot springs, and water treatment plants.[8]

Following its isolation, N. moscoviensis’s genome was sequenced by Dr. Ehrich et al.[2] Its 4.59 Mb genome has a GC content of 56.9+/-0.4 mol% with a predicted 4,863 coding sequences.[2][3] N. moscoviensis's 16S rRNA gene sequences were found to be 88.9% similar to N. marina’s.[2] Despite its relatively low similarity to N. marina, N. moscoviensis was classified within the Nitrospirae phylum primarily due to shared morphological features including the presence of an enlarged periplasmic space.[2]

N. moscoviensis’s fully sequenced genome has provided useful phylogenetic insights beyond the scope of 16S rRNA sequence studies.[7] The discovery of the gene encoding the β-subunit of nitrite-oxidoreductase, nxrB, from N. moscoviensis as a functional genetic marker of Nitrospira, not only confirmed previous 16S rRNA phylogenetic classifications within the phylum, but revealed a new understanding of Nitrospira’s richness in terrestrial environments.[7] The phylum has expanded from two bacteria, N. marina and N. moscoviensis, to a 6-branched genera composed of a characteristically diverse group of nitrite-oxidizing bacteria with N. moscoviensis positioned in lineage II.[8]

The cytoplasm of Nitrospira moscoviensis contains polyhydroxybutyrate (PHB) granules.[2]

• Neubacher, Elke; Prast, Mario; Cleven, Ernst-Josef; Berninger, Ulrike-Gabriele (2007). "Ciliate grazing on Nitrosomonas europaea and Nitrospira moscoviensis: Is selectivity a factor for the nitrogen cycle in natural aquatic systems?". Hydrobiologia. 596 (1): 241–250. doi:10.1007/s10750-007-9100-7. ISSN 0018-8158. S2CID 28520940.
• Lucker, S.; Wagner, M.; Maixner, F.; Pelletier, E.; Koch, H.; Vacherie, B.; Rattei, T.; Damste, J. S. S.; Spieck, E.; Le Paslier, D.; Daims, H. (2010). "A Nitrospira metagenome illuminates the physiology and evolution of globally important nitrite-oxidizing bacteria". Proceedings of the National Academy of Sciences. 107 (30): 13479–13484. doi:10.1073/pnas.1003860107. ISSN 0027-8424. PMC 2922143. PMID 20624973.

• MicrobeWiki – Nitrospira
• "Nitrospira moscoviensis" at the Encyclopedia of Life
• LPSN