Denitrobacterium | |
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Genus: | Denitrobacterium Anderson et al. 2000 [1] |
Type species | |
Denitrobacterium detoxificans Anderson et al. 2000 | |
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Denitrobacterium is a genus of Actinomycetota with a single species, in the family Coriobacteriaceae. Originally isolated from the bovine rumen, Denitrobacterium are non-motile and non-spore forming. [3] The only described species in this genus is Denitrobacterium detoxificans. [1] The specific niche of this bacterium in the bovine rumen is theorized to be the detoxification/metabolism of nitrotoxins and miserotoxin. [4] [5] [6]
The sole species currently described in the genus Denitrobacterium, D. detoxificans, is a Gram-positive, obligate anaerobe. [3] In the study conducted by Anderson et al., [3] all of the four strains (NPOH1, NPOH2, NPOH3, and MAJ1) are shown to possess high G+C content in their DNAs (60, 58, 56, and 60 mol%, respectively) and are closely related to one another (more than 99% sequence identity). Additionally, the closest intergeneric relative is Coriobacterium glomerans with 86% sequence identity, based on the 16S rRNA sequence comparison between the NPOH1 strain and sequences available in GenBank. [3]
In the bovine rumen, Denitrobacterium detoxificans metabolizes the following substrates through oxidation: [3] [7]
The oxidation of these above compounds are coupled with the reduction of nitrocompounds such as: [3] [7]
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. [8] β-alanine is further metabolized by ruminal microorganisms, whereas aminopropanol seems to be a final product. [8] 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. [9] 3NPA gets metabolized by ruminal microbes more rapidly than 3NPOH; [10] [9] [11] therefore, 3NPA is less toxic to ruminants grazing on leguminous plants containing the conjugates of these nitrocompounds than 3NPOH. [11] [8]
The above nitrocompounds are abundant in many forages in the forms of glycosides and glucose esters. [12] Miserotoxin is the most common glycoside of 3NPOH as 3-nitro-1-propyl-β-D-glucopyranoside, first isolated from Astragalus oblongifolius. [13] Other glycosides of 3NPOH include β-D-gentiobioside, [14] allolactoside, [15] laminaribioside, [16] and cellobioside [17] from Astragalus miser var. serotinus. [12] Glucose esters of 3NPA are produced by species of the genera Coronilla [18] [19] [20] , Astragalus [21] , Indigofera [21] [22] [23] [24] , and Hiptage [22] . [12] 3NPA is also produced by Astragalus canadensis in the forms of oxotetrahydrofuranyl [25] and isoxazolinone esters. [26] [12]
The D. detoxifican strain NPOH1 was first isolated and cultured in the 1996 study by Anderson et al., [4] 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. [4] 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. [3] [4]
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. [3] The genus Denitrobacterium was included in the family Coriobaceteriaceae by Zhi et al. in the 2009 publication [27] on addendum to the class Actinobacteria.