Phenotypic characteristics of nitrate and 3-nitro-1-propionate-respiring enzymes of the obligate respiratory anaerobe Denitrobacterium detoxificans

Authors: Anderson, Robin; LATHAM, ELIZABETH - Texas A&M University; PINCHAK, WILLIAM - Texas A&M University; Nisbet, David

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/2/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Anaerobic respiration consumes reducing equivalents generated during fermentation thereby contributing to the maintenance of hydrogen homoeostasis in gut ecosystems. Nitrate and 3-nitro-1-propionate (NPA) are acceptors used by the nonfermentative, rumen anaerobe, Denitrobacterium detoxificans, which are reduced to ammonia and ß-alanine, respectively. Basic local alignment search tool (BLAST) analysis of the D. detoxificans strain NPOH1 genome revealed near equal numbers of genes encoding periplasmic and membrane-bound nitrate reductases and two potential nitroalkane-metabolizing genes. Phenotypic characterizations of these enzymes in D. detoxificans are lacking. Presently, we found that when D. detoxificans was grown with 6 mM nitrate, reductant supplied as 16 µmol formate/mL supported more than 2-fold higher growth rates and maximum optical densities than did 30 µmol hydrogen/mL (0.008 h**-1 and 0.058 at 600 nm). Growth rates and maximum optical densities during growth with 10 mM NPA were 1.4- to 2.5-fold higher with formate than with hydrogen (0.005 h**-1 and 0.056 at 600 nm). Supplemental tungsten (50 mM), a valence state analogue of molybdenum, inhibited nitrate- and NPA-supported growth rates by more than 3-fold. Tungsten inhibited maximum optical densities of nitrate-grown cultures by up to 3-fold and more than 18-fold for NPA-grown cultures. These results implicate involvement of molybdenum-containing coenzymes. Nitrate-supported growth of D. detoxificans was not diminished by supplemental chlorate (6 mM) when grown with either formate or hydrogen. Conversely, maximal optical densities for NPA-grown D. detoxificans were decreased more than 4-fold by supplemental chlorate compared to nonchlorate-treated cultures, with the decrease being more with hydrogen than formate. Growth rates were slower, albeit not significantly, for chlorate-supplemented cultures grown with NPA regardless of the reductant. Chlorate by itself did not support growth of D. detoxificans. These results suggest a chlorate-insensitive periplasmic nitrate reductase may be involved in nitrate respiration by D. detoxificans and that a chlorate-sensitive membrane-bound reductase may contribute to NPA respiration by this bacterium.