7,629 research outputs found
Comparison of bacterioneuston and bacterioplankton dynamics during a phytoplankton bloom in a fjord mesocosm
The bacterioneuston is the community of Bacteria present in surface microlayers, the
thin surface film that forms the interface between aquatic environments and the
atmosphere. In this study we compared bacterial cell abundance and bacterial
community structure of the bacterioneuston and the bacterioplankton (from the
subsurface water column) during a phytoplankton bloom mesocosm experiment.
Bacterial cell abundance, determined by flow cytometry, followed a typical
bacterioplankton response to a phytoplankton bloom, with Synechococcus and high
nucleic acid (HNA) bacterial cell numbers initially falling, probably due to selective
protist grazing. Subsequently HNA and low nucleic acid (LNA) bacterial cells
increased in abundance but Synechococcus did not. There was no significant
difference between bacterioneuston and bacterioplankton cell abundances during the
experiment. Conversely, distinct and consistent differences between the
bacterioneuston and the bacterioplankton community structure were observed. This
was monitored simultaneously by Bacteria 16S rRNA gene terminal restriction
fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis
(DGGE). The conserved patterns of community structure observed in all of the
mesocosms indicate that the bacterioneuston is distinctive and non-random
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 ∼17% 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 “Innovative and practical management approaches to reduce nitrogen excretion by ruminants (Rednex)” 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
Not all saponins have a greater antiprotozoal activity than their related sapogenins
The antiprotozoal effect of saponins varies according to both the structure of the sapogenin and the composition and linkage of the sugar moieties to the sapogenin. The effect of saponins on protozoa has been considered to be transient as it was thought that when saponins were deglycosilated to sapogenins in the rumen they became inactive; however, no studies have yet evaluated the antiprotozoal effect of sapogenins compared to their related saponins. The aims of this study were to evaluate the antiprotozoal effect of eighteen commercially available triterpenoid and steroid saponins and sapogenins in vitro, to investigate the effect of variations in the sugar moiety of related saponins and to compare different sapogenins bearing identical sugar moieties. Our results show that antiprotozoal activity is not an inherent feature of all saponins and that small variations in the structure of a compound can have a significant influence on their biological activity. Some sapogenins (20(S)-protopanaxatriol, asiatic acid and madecassic acid) inhibited protozoa activity to a greater extent than their corresponding saponins (Re and Rh1 and asiaticoside and madecassoside), thus the original hypothesis that the transient nature of the antiprotozoal action of saponins is due to the deglycosilation of saponins needs to be revisited.This work was supported by the Innovate UK project ‘Ivy for ruminants’ Ref:101091. CJN thanks the Biotechnology and Biological Sciences Research Council, UK via grant number BB/J0013/1, for financial support
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