ISSN:
1550-7408
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Experiments with washed suspensions of holotrich protozoa (Isotricha spp. and Dasytricha ruminantium) showed that both organisms have an efficient 0,-scavenging capability (apparent Km values 2.3 and 0.3 μM, respectively). Reversible inhibition of H2, production increased almost linearly with increasing O2 up to 1.5 μM; higher levels of O2 gave irreversible inhibition. In situ determinations of H, CH4, O2, and CO2, in ovine rumen liquor, using a membrane inlet mass spectrometer probe, indicated that O2, 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 O2. concentration after feeding occurred only in defaunated animals and resulted in suppression of CH4 and CO2 production. The presence of washed holotrich protozoa decreases the O2 sensitivity of CH4 production by suspensions of a cultured methanogenic bacterium Methanosarcina barkeri. It is concluded that holotrich protozoa play a role in ruminal O2 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 O2 levels, and are themselves regulated by the low ambient O2 concentrations they experience in the rumen.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1550-7408.1989.tb01075.x
