Denitrobacterium

In the bovine rumen, Denitrobacterium detoxificans metabolizes the following substrates through oxidation:[1][6]

• Hydrogen
• Formate
• Lactate

The oxidation of these above compounds are coupled with the reduction of nitrocompounds such as:[1][6]

• 3-nitro-1-propionic acid (3NPA)
• 3-nitro-1-propanol (3NPOH)
• 2-nitroethane (2NEOH), an analogue of 3NPOH

There are speculations as to how these nitrocompounds are metabolized. The primary mechanism of 3NPA and 3NPOH metabolism is the reduction to amines, i.e. β-alanine and aminopropanol, respectively.[7] β-alanine is further metabolized by ruminal microorganisms, whereas aminopropanol seems to be a final product.[7] It is also speculated that nitrite may be cleaved off from both 3NPA and 3NPOH as a minor metabolite, which is then further reduced to ammonia.[8]3NPA gets metabolized by ruminal microbes more rapidly than 3NPOH;[9][8][10] therefore, 3NPA is less toxic to ruminants grazing on leguminous plants containing the conjugates of these nitrocompounds than 3NPOH[10].[7]

The above nitrocompounds are abundant in many forages in the forms of glycosides and glucose esters.[11] Miserotoxin is the most common glycoside of 3NPOH as 3-nitro-1-propyl-β-_D-glucopyranoside, first isolated from Astragalus oblongifolius.[12] Other glycosides of 3NPOH include β-_D-gentiobioside,[13] allolactoside,[14] laminaribioside,[15] and cellobioside[16] from Astragalus miser var. serotinus.[11] Glucose esters of 3NPA are produced by species of the genera Coronilla[17][18][19], Astragalus[20], Indigofera[20][21][22][23], and Hiptage[24].[11] 3NPA is also produced by Astragalus canadensis in the forms of oxotetrahydrofuranyl[25] and isoxazolinone esters[26].[11]

The D. detoxifican strain NPOH1 was first isolated and cultured in the 1996 study by Anderson et al.,[3] investigating the metabolism of nitrotoxins such as 3-nitro-1-propanol and 3-nitro-1-propionate. Strains NPOH2 and NPOH3 were isolated from a roll tube containing an agar medium with energy-depleted rumen fluid (at 40% v/v), sodium carbonate, resazurin, _L-cysteine-HCl, lipoic acid, vitamins, minerals, and Amisoy (a partially purified soy protein product by Quest International, at 0.08% w/v), supplemented with 9 mM 3-nitro-1-propanol and inoculated with 2 x 10⁻⁴ mL of nonenriched ruminal fluid.[3] The rumen contents containing NPOH1, NPOH2, and NPOH3 were obtained from two different cows (one with NPOH1 and another with NPOH2&3) at the National Animal Disease Center (NADC) in Ames, IA, USA. Strain MAJ1 was isolated from rumen contents of a cow on a milkvetch range harboring Astragalus miser var. serotinus in British Columbia, Canada.[1][3]

In the 2000 article, Anderson et al. proposed the assignment of the novel bacteria into the class Actinobacteria, subclass Coriobacteridae, order Coriobacteriales, family Coriobacteriaceae based on the high mole percent G+C content and 16S rRNA sequence.[1] The genus Denitrobacterium was included in the family Coriobaceteriaceae by Zhi et al. in the 2009 publication[27] on addendum to the class Actinobacteria.