73 research outputs found
Study of methanogen communities associated with different rumen protozoal populations
Protozoa-associated methanogens (PAM) are considered one of the most active communities in the rumen methanogenesis. This experiment investigated whether methanogens are sequestrated within rumen protozoa, and structural differences between rumen free-living methanogens and PAM. Rumen protozoa were harvested from totally faunated sheep, and six protozoal fractions (plus free-living microorganisms) were generated by sequential filtration. Holotrich-monofaunated sheep were also used to investigate the holotrich-associated methanogens. Protozoal size determined the number of PAM as big protozoa had 1.7â3.3 times more methanogen DNA than smaller protozoa, but also more endosymbiotic bacteria (2.2- to 3.5-fold times). Thus, similar abundance of methanogens with respect to total bacteria were observed across all protozoal fractions and free-living microorganisms, suggesting that methanogens are not accumulated within rumen protozoa in a greater proportion to that observed in the rumen as a whole. All rumen methanogen communities had similar diversity (22.2 ± 3.4 TRFs). Free-living methanogens composed a conserved community (67% similarity within treatment) in the rumen with similar diversity but different structures than PAM (P < 0.05). On the contrary, PAM constituted a more variable community (48% similarity), which differed between holotrich and total protozoa (P < 0.001). Thus, PAM constitutes a community, which requires further investigation as part of methane mitigation strategies
Bacterial protein degradation by different rumen protozoal groups
Bacterial predation by protozoa has the most deleterious effect on the efficiency of N use within the rumen, but differences in activity among protozoal groups are not completely understood. Two in vitro experiments were conducted to identify the protozoal groups more closely related with rumen N metabolism. Rumen protozoa were harvested from cattle and 7 protozoal fractions were generated immediately after sampling by filtration through different nylon meshes at 39°C, under a CO2 atmosphere to maintain their activity. Protozoa were incubated with 14C-labeled bacteria to determine their bacterial breakdown capacity, according to the amount of acid-soluble radioactivity released. Epidinium tended to codistribute with Isotricha and Entodinium with Dasytricha; therefore, their activity was calculated together. This study demonstrated that big Diplodiniinae had the greatest activity per cell (100 ng bacterial CP per protozoa and hour), followed by Epidinium plus Isotricha (36.4), small Diplodiniinae (34.2), and Entodinium plus Dasytricha (14.8), respectively. However, the activity per unit of protozoal volume seemed to vary, depending on the protozoal taxonomy. Small Diplodiniinae had the greatest activity per volume (325 ng bacterial CP per protozoal mm3 and hour), followed by big Diplodiniinae (154), Entodinium plus Dasytricha (104), and Entodinium plus Dasytricha (25.6). A second experiment was conducted using rumen fluid from holotrich-monofaunated sheep. This showed that holotrich protozoa had a limited bacterial breakdown capacity per cell (Isotricha 9.44 and Dasytricha 5.81 ng bacterial CP per protozoa and hour) and per protozoal volume (5.97 and 76.9 ng bacterial CP per protozoal mm3 and hour, respectively). Therefore, our findings indicated that a typical protozoal population (106 total protozoa/mL composed by Entodinium sp. 88%, Epidinium sp. 7%, and other species 4%) is able to break down âŒ17% of available rumen bacteria every hour. Entodinium sp. is responsible for most of this bacterial breakdown (70 to 75%), followed by Epidinium sp. (16 to 24%), big Diplodiniinae (4 to 6%), and small Diplodiniinae (2 to 6%), whereas holotrich protozoa have a negligible activity (Dasytricha sp. 0.6 to 1.2% and Isotricha sp. 0.2 to 0.5%). This in vitro information must be carefully interpreted, but it can be used to indicate which protozoal groups should be suppressed to improve microbial protein synthesis in vivo.This study was supported by the Framework 7 program from the EU âInnovative and practical management approaches to reduce nitrogen excretion by ruminants (Rednex)â and the Welsh government. We thank the Institute of Biological, Environmental and Rural Sciences staff for their assistance and collaboration
Effect of diet and absence of protozoa on the rumen microbial community and on the representativeness of bacterial fractions used in the determination of microbial protein synthesis
Accurate estimates of microbial synthesis
in the rumen are vital to optimize ruminant nutrition.
Liquid- (LAB) and solid-associated bacterial fractions
(SAB) harvested from the rumen are generally considered
as microbial references when microbial yield is
calculated; however, factors that determine their composition
are not completely understood. The aim of this
study was to evaluate the effect of diet and absence or
presence of rumen protozoa on the rumen microbial
community. It was hypothesized that these treatments
could modify the composition and representativeness
of LAB and SAB. Twenty twin lambs (Ovis aries) were
used; one-half of the twins were kept protozoa-free, and
each respective twin sibling was faunated. At 6 mo of
age, 5 animals from each group were randomly allocated
to the experimental diets consisting of either alfalfa
hay as the sole diet, or 50:50 mixed with ground barley
grain. After 15 d of adaptation to the diet, animals
were euthanized, rumen and abomasum contents were sampled, and LAB and SAB isolated. The presence
of protozoa buffered the effect of diet on the rumen
bacterial population. Faunated animals fed alfalfa hay
had a greater abundance of F. succinogenes, anaerobic
fungi and methanogens, as well as an enhanced rumen
bacterial diversity. Cellulolytic bacteria were more
abundant in SAB, whereas the abomasal abundance
of most of the microorganisms studied was closer to
those values observed in LAB. Rumen and abomasal
samples showed similar bacterial DNA concentrations,
but the fungal and protozoal DNA concentration in the
abomasum was only 69% and 13% of that observed in
the rumen, respectively, suggesting fungal and protozoal
sequestration in the rumen or possible preferential
degradation of fungal and protozoal DNA in the abomasum,
or both. In conclusion, absence of protozoa and
type of diet extensively modifi ed the chemical composition
of LAB and SAB as a consequence of changes in
the microbial composition of these fractions
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