No abstract

The variation of the composition in species of host communities can modify the risk of disease transmission. In particular, the introduction of a new host species can increase health threats by adding a new reservoir and/or by amplifying the circulation of either exotic or native pathogens. Lyme borreliosis is a multi-host vector-borne disease caused by bacteria belonging to the Borrelia burgdorferi sensu lato complex. It is transmitted by the bite of hard ticks, especially Ixodes ricinus in Europe. Previous studies showed that the Siberian chipmunk, Tamias sibiricus barberi, an introduced ground squirrel in the Forest of Sénart (near Paris, France) was highly infested by I. ricinus, and consequently infected by B. burgdorferi sl. An index of the contribution of chipmunks to the density of infected questing nymphs on the vegetation (i.e., the acarological risk for humans) was compared to that of bank voles (Myodes glareolus) and of wood mice (Apodemus sylvaticus), two known native and sympatric competent reservoir hosts. Chipmunks produced nearly 8.5 times more infected questing nymphs than voles and mice. Furthermore, they contribute to a higher diversity of B. burgdorferi sl genospecies (B. afzelii, B. burgdorferi sensu stricto and B. garinii). The contribution of chipmunks varied between years and seasons, according to tick availability. As T. s. barberi must be a competent reservoir, it should amplify B. burgdorferi sl infection, hence increasing the risk of Lyme borreliosis in humans.

We investigated the influence of the composition of the fibrolytic microbial community on the development and activities of hydrogen-utilizing microorganisms in the rumens of gnotobiotically reared lambs. Two groups of lambs were reared. The first group was inoculated with Fibrobacter succinogenes, a non-H 2 -producing species, as the main cellulolytic organism, and the second group was inoculated with Ruminococcus albus, Ruminococcus flavefaciens, and anaerobic fungi that produce hydrogen. The development of hydrogenotrophic bacterial communities, i.e., acetogens, fumarate and sulfate reducers, was monitored in the absence of methanogens and after inoculation of methanogens. Hydrogen production and utilization and methane production were measured in rumen content samples incubated in vitro in the presence of exogenous hydrogen (supplemented with fumarate or not supplemented with fumarate) or in the presence of ground alfalfa hay as a degradable substrate. Our results show that methane production was clearly reduced when the dominant fibrolytic species was a non-H 2 -producing species, such as Fibrobacter succinogenes, without significantly impairing fiber degradation and fermentations in the rumen. The addition of fumarate to the rumen contents stimulated H 2 utilization only by the ruminal microbiota inoculated with F. succinogenes, suggesting that these communities could play an important role in fumarate reduction in vivo.Hydrogen is a major intermediary metabolite in anaerobic degradation of organic matter. In ruminants, hydrogen is produced by hydrolytic and fermentative microorganisms and is mainly used by methanogenic Archaea to reduce carbon dioxide into methane. These microorganisms represent the main ruminal microbial community implicated in this pathway (33). Hydrogen transfer through methanogenesis is beneficial to the degradation of plant cell wall carbohydrates in the rumen (19,43,46). However, as a result of this process, methane is eructated by ruminants (400 to 500 liters per day per adult animal) and represents a loss of carbon and energy, accounting for 8 to 12% of the gross energy content of the diet (27, 37, 44). The amount of methane produced varies according to the diet (forage or concentrate) and the production system (intensive or extensive) (27,40). The contribution of livestock agriculture to greenhouse gas (GHG) emissions has been estimated to range between 9% and 18% of anthropogenic emissions, with methane representing between 30% and 50% of the total GHG emitted from the livestock sector (34). In that context, various strategies have been suggested in order to mitigate ruminant methane production (27,28,34). Reducing hydrogen production should be achieved without impairing efficacy of feed digestion and fermentation. Inhibition of activity and/or number of methanogens should be done in association with a stimulation of hydrogen-consuming pathways in order to avoid the negative effect of an increased partial pressure of this gas (28).The aim of the present work was to investigate t...

We investigated the potential of the ruminant feed additive Saccharomyces cerevisiae CNCM I-1077 on protein and peptide degrading activities of the rumen bacterial species Prevotella albensis M384, Streptococcus bovis 20480, and Butyrivibrio fibrisolvens 3071 grown in vitro. Alive or heat-killed yeast cells were added to bacterial cultures in a complex casein-glucose medium. After incubation of the cultures at 39 degrees C under O(2)-free CO(2), peptidase activities were determined in the absence or in the presence of yeasts. Protease activities were detected after PAGE in gelatin-copolymerized gels. In co-incubations of bacteria and live S. cerevisiae I-1077, proteinase activities were reduced compared to the activities in the bacterial monocultures. Measurement of peptidase activities and microbial enumerations in the co-incubations suggested that live yeasts and bacteria interacted in a competitive way, leading to a decrease in peptidase activities. The mechanism responsible for such an effect could be mainly a competition for substrate utilization, but the release of small competitive peptides by the yeast cells is also likely to be implicated.