Nitrospira moscoviensis was the second bacterium classified under the most diverse nitrite-oxidizing bacteria phylum, Nitrospirae.[2][3] It is a gram-negative, non-motile, facultative lithoauthotropic bacterium that was discovered in Moscow, Russia in 1995.[2] The genus name, Nitrospira, originates from the prefix “nitro” derived from nitrite, the microbe’s electron donor and “spira” meaning coil or spiral derived from the microbe’s shape.[4] The species name, moscoviensis, is derived from Moscow, where the species was first discovered.[4]N. moscoviensis could potentially be used in the production of bio-degradable polymers.[2]
History
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 her 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]
Morphology
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]
Metabolism
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]
Ecology
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]
Genomics
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]
Nitrospira 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]
Biotechnology
The cytoplasm of Nitrospira moscoviensis contains polyhydroxybutyrate (PHB) granules.[2]
^ abWatson, S.W.; Bock, E.; Valois, F.W.; Waterbury, J.B.; Schlosser, U (1986). "Nitrospira marina gen. nov. sp. nov.: a chemolitho- trophic nitrite-oxidizing bacterium". Arch Microbiol. 144 (1): 1–7. doi:10.1007/BF00454947. S2CID29796511.
^ abcdefSpieck, E.; Ehrich, S; Aamand, J; Bock, E. (1998). "Isolation and immunocytochemical location of the nitrite-oxidizing system in nitrospira moscoviensis". Arch Microbiol. 169 (3): 225–230. doi:10.1007/s002030050565. PMID9477257. S2CID21868756.
^Kirstein, K; Bock, E (1993). "Close genetic relationship between Ni- trobacter hamburgensis nitrite oxidoreductase and Escherichia coli nitrate reductases". Arch Microbiol. 160 (6): 447–453. doi:10.1007/BF00245305. PMID8297210. S2CID22834340.
