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A molecular-based examination of the glutamate dehydrogenase and glutamine synthetase of ruminal Prevotella spp.
Abstract
One of the ultimate goals of ruminant animal enterprises is to optimize the supply of amino acids to the host animals, and limit nitrogen excretion in animal waste, which could be an economical and environmental dilemma especially for intensive livestock industries. In many situations rumen microbial protein is the predominant source of amino acids for the ruminant. Therefore, factors which affect microbial growth rate and yield of biomass directly affect the quantity of protein available to the ruminants. The bacteria chosen for study, Prevotella spp. are widely considered to have a central role in the nitrogen economy of the rumen. The studies presented in this thesis represent the first molecular-based characterization of nitrogen assimilation by a ruminal bacterium. Glutamate dehydrogenase is a key enzyme that links carbohydrate and nitrogen metabolism. All Prevotella strains tested possess glutamate dehydrogenase activities. Maximal activities are measured in cells grown under ammonium limitation, and peptides as a source of nitrogen strongly inhibit the NADPH-utilizing activity, which in P. bryantii, is nitrogen regulated at the level of transcription. The structural gene gdhA of P. bryantii is cloned and mutation of gdhA does not alter cell growth on ammonium. Glutamine synthetase in enterobacteria has a dual role of providing glutamine and assimilating ammonia. Small amounts of glutamine synthetase activity are detectable in P. bryantii. The activity is maximal when the bacterium is under ammonium limitation. Ammonium excess and presence of peptides decrease enzyme activity, presumably due to lower level of transcription in response to the nitrogen status. The structural gene glnN is cloned and the encoded protein is typical of type III enzymes. Glutamine synthetase in this bacterium is required for growth in providing glutamine, but an alternative route of ammonia assimilation and glutamate biosynthesis is functional. These studies present evidence that Prevotella and other members of Bacteroideaceae execute ammonia assimilation and nitrogen regulation by a mechanism that differs from the enterobacteria, and appears to have more in common with photosynthetic cyanobacteria.
Subject Area
Microbiology|Livestock
Recommended Citation
Wen, Zezhang Tom, "A molecular-based examination of the glutamate dehydrogenase and glutamine synthetase of ruminal Prevotella spp." (1998). ETD collection for University of Nebraska-Lincoln. AAI9826108.
https://digitalcommons.unl.edu/dissertations/AAI9826108