Characteristics of a nitropropanol-metabolizing bacterium isolated from the rumen

Abstract

We report some characteristics of a ruminal bacterium (strain NPOH1) that metabolizes 3-nitropropanol, the toxic principle of various milk vetchs that are distributed worldwide. The gram-positive bacterium was nonmotile and did not produce spores. Growth of strain NPOH1 occurred under anaerobic conditions and was supported by the electron acceptors 3-nitropropanol, 3-nitropropionate, nitrate, 2-nitropropanol, nitroethane, nitroethanol, or 3-nitro-1-propyl-beta-D-glucopyranoside (miserotoxin). Other potential electron acceptors, namely sulfate, sulfite, azide, chlorate, perchlorate, nitrite, fumarate, 2-nitrobutane, or nitrobenzene, did not support growth. Formate, lactate, and H2 stimulated growth of strain NPOH1 in the presence of the appropriate nitrocompound, whereas a variety of other potential H2 donors did not. When grown in medium containing both nitrate and either 3-nitropropanol or 3-nitropropionate, nitrate was the preferred acceptor. Strain NPOH1 reduced nitrate to nitrite and, when grown with excess reductant, nitrite was further reduced to ammonia. The products formed during the metabolism of 3-nitropropanol and 3-nitropropionate by mixed ruminal populations, 3-aminopropanol and beta-alanine, were not found in culture fluids of strain NPOH1. Analysis of total cellular fatty acid profiles and of the mole percent guanine plus cytosine suggests that strain NPOH1 is a novel bacterium. The capacity of strain NPOH1 to metabolize 3-nitropropanol suggests that this organism may play an important role in detoxification of 3-nitropropanol in the rumen.

Denitrobacterium detoxificans gen. nov., sp. nov., a ruminal bacterium that respires on nitrocompounds.

“…The potential electron acceptors chlorate, fumarate, nitrite, perchlorate, sulfate and sulfite did not support growth of any of the strains. In agreement with an earlier report (Anderson et al, 1997), growth of strain NPOH1 T was also supported by nitrate but none of the other three strains were able to grow with nitrate as a terminal electron acceptor (Table 1). In the case of strain NPOH1 T , nitrate was reduced to nitrite, which was then reduced to am- 0n00 0n22 0n30 0n22 0n36 0n08 0n44 0n06 0n10 0n28 0n25 NPOH2 0n00 0n17 0n17 0n22 0n33 0n11 0n00 0n04 0n09 0n22 0n14 NPOH3 0n00 0n17 0n27 0n28 0n43 0n10 0n00 0n04 0n07 0n30 0n25 MAJ1 0n00 0n27 0n10 0n30 0n40 0n12 0n00 0n03 0n10 0n35 0n22…”

“…We thus propose that these nitrocompoundrespiring organisms be designated Denitrobacterium detoxificans gen. nov., sp. nov. Strain NPOH1 T , which has been characterized in this and in an earlier report (Anderson et al, 1997), is proposed as the type strain of the species. Electron micrographs depicting cell morphology and cell wall structure of strain NPOH1 T have been published earlier (Anderson et al, 1997).…”

“…Ruminants gradually adapted to forages containing these toxins can acquire a tolerance resulting from enhanced ruminal detoxification and evidence suggests that bacteria like the one isolated by us may play a major role in this detoxification (Anderson et al, 1998 ;Majak, 1992). late, strain NPOH1 T , it became apparent that this anaerobe differed markedly from known bacteria (Anderson et al, 1997). We now report results from phenotypic and genotypic characterizations of this and other recently isolated nitrotoxin-metabolizing bacteria.…”

“…Tests for indole and H # S production were performed using medium B supplemented with 9 mM nitropropanol, 5 mM formate, -tryptophan (0n1%, w\v) or with ferrous sulfate and sodium thiosulfate (0n015 %, w\v, each) as previously described (Anderson et al, 1997). Medium B supplemented with 9 mM nitropropanol, 5 mM formate and 4 % gelatin was used to test for gelatin hydrolysis (Anderson et al, 1997). All culture tests were performed at least twice and mean results are reported.…”

Journal of Range Management, Volume 56, Number 3 (May 2003)

“…Rumen bacteria also have the capacity to degrade and detoxify NPOH, and the rate of degradation can be enhanced by increasing the amount of protein in the diet . The detoxification of NPOH by Denitrobacterium detoxificans, a recently identified rumen bacterium, involves the reduction of the nitro group to the much less toxic amino group (Anderson et al 1993(Anderson et al , 1997. One strain of this bacterium (MAJI) originated from the rumen bacteria of cattle grazing our study area in the Cariboo (Anderson et al 2000).…”