Diversity of locust gut bacteria protects against pathogen invasion

Diversity-invasibility relationships were explored in the novel context of the colonization resistance provided by gut bacteria of the desert locust Schistocerca gregaria against pathogenic bacteria. Germ-free insects were associated with various combinations of one to three species of locust gut bacteria and then fed an inoculum of the pathogenic bacterium Serratia marcescens. There was a significant negative relationship between the resulting density of Serratia marcescens and the number of symbiotic gut bacterial species present. Likewise there was a significant inverse relationship between community diversity and the proportion of locusts that harboured Serratia. Host mortality was not negatively correlated with resistance to gut-invasion by Serratia marcescens, although there were significantly more deaths among pathogen fed germ-free insects than tri-associated gnotobiotes. The outcome is consistent with the predictions of community ecology theory that species-rich communities are more resistant to invasion than species-poor communities

Síntese de proteína microbiana e concentrações de uréia em vacas alimentadas com diferentes fontes de proteína Estimation of microbial protein synthesis and urea nitrogen metabolism in lactating dairy cows fed diets supplemented with different protein sources

Foram utilizadas 12 vacas Holandesas puras e mestiças, distribuídas em três quadrados latinos 4 x 4, organizados de acordo com os dias em lactação, com o objetivo de avaliar o efeito de diferentes fontes protéicas sobre a síntese, a eficiência de síntese de proteína microbiana, a concentração de nitrogênio uréico no soro (NUS) e no leite (NUL), a concentração de nitrogênio amoniacal e o pH ruminal. Utilizou-se silagem de milho como volumoso, na proporção de 60% da MS total. Os concentrados foram constituídos de diferentes fontes protéicas (FS - farelo de soja; FA38 - farelo de algodão 38%PB; FA28 - farelo de algodão 28%PB e FSU - farelo de soja + 5% de uréia/sulfato de amônia na MS do concentrado). As coletas spot de urina e de sangue foram realizadas no 18º dia do período experimental 4 horas após o fornecimento da alimentação aos animais, no período da manhã. Não foram observadas diferenças entre as dietas para o volume urinário (V), a excreção total de derivados de purinas (PT), a síntese e a eficiência de síntese de PB microbiana, expressa em g de PB/kg de NDT consumido. As concentrações de NUS e NUL também não diferiram entre as dietas. As concentrações de NUS e NUL e a síntese de PB microbiana não foram influenciadas pelas diferentes fontes de proteína dietéticas, inclusive com a adição de uréia (5% MS do concentrado).<br>Twelve Holstein lactating dairy cows were blocked by days in milk and randomly assigned to three replicated 4 x 4 Latin square to evaluate the effect of different protein sources on efficiency of microbial protein synthesis, concentration of serum (NUS) and milk (MUN) urea nitrogen, and ruminal metabolism. A basal corn silage diet (60% of the total dry matter) was fed plus one of the following proteins sources (DM basis): soybean meal (SBM), cottonseed meal with 38% of crude protein (CSM38), cottonseed meal with 28% of crude protein (CSM28), or soybean meal plus 5% of urea/ammonium sulfate (SBMU). Each experimental period lasted 18 days with 11 days for diet adaptation and seven days for sample collection. Samples of urine and blood were obtained approximately four hours after the morning feeding on day 18 of each period. No significant differences among diets were observed for urinary volume (V), total purine derivatives excretion (PT), microbial CP synthesis and microbial efficiency, expressed in g of CP/kg of TDN intake. In addition, concentration of both NUS and MUN also did not differ among diets. It can be concluded that NUS and MUN as well as microbial CP synthesis and efficiency were not affected by feeding different protein sources to lactating dairy cows