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Hydrogen Production by Rumen Holotrich Protozoa: Effects of Oxygen and Implications for Metabolic Control by In Situ Conditions
Author(s) -
HILLMAN D. LLOYD. K.,
YARLETT N.,
WILLIAMS A. G.
Publication year - 1989
Publication title -
the journal of protozoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 0022-3921
DOI - 10.1111/j.1550-7408.1989.tb01075.x
Subject(s) - rumen , protozoa , fermentation , bacteria , biology , food science , in situ , chemistry , biochemistry , zoology , microbiology and biotechnology , genetics , organic chemistry
Experiments with washed suspensions of holotrich protozoa (Isotricha spp. and Dasytricha ruminantium ) showed that both organisms have an efficient 0,‐scavenging capability (apparent K m values 2.3 and 0.3 μM, respectively). Reversible inhibition of H 2 , production increased almost linearly with increasing O 2 up to 1.5 μM; higher levels of O 2 gave irreversible inhibition. In situ determinations of H, CH 4 , O 2 , and CO 2 , in ovine rumen liquor, using a membrane inlet mass spectrometer probe, indicated that O 2 , was present before feeding at 1‐1.5 μM and decreased to undetectable levels (<0.25 μM) within 25 min after feeding. A transient increase in O 2 . concentration after feeding occurred only in defaunated animals and resulted in suppression of CH 4 and CO 2 production. The presence of washed holotrich protozoa decreases the O 2 sensitivity of CH 4 production by suspensions of a cultured methanogenic bacterium Methanosarcina barkeri . It is concluded that holotrich protozoa play a role in ruminal O 2 utilization as well as in the production of fermentation end products (especially short‐chain volatile fatty acids) utilized by the ruminant and H, utilized by methanogenic bacteria. These hydrogenosome‐containing protozoa thus both control patterns of fermentation by influencing O 2 levels, and are themselves regulated by the low ambient O 2 concentrations they experience in the rumen.