Phylogenetics and the cohesion of bacterial genomes

Gene acquisition is an ongoing process in many bacterial genomes, contributing to adaptation and ecological diversification. Lateral gene transfer is considered the primary explanation for discordance among gene phylogenies and as an obstacle to reconstructing the tree of life. We measured the extent of phylogenetic conflict and alien-gene acquisition within quartets of sequenced genomes. Although comparisons of complete gene inventories indicate appreciable gain and loss of genes, orthologs available for phylogenetic reconstruction are consistent with a single tree.     

Sensory-directed identification of creaminess-enhancing volatiles and semivolatiles in full-fat cream

Aimed at defining the chemical nature of creaminess-related flavor compounds in dairy products on a molecular level, a full-fat cream was analyzed for sensorially active volatiles and semivolatiles by means of activity-guided screening techniques. Application of the aroma extract dilution analysis on an aroma distillate prepared from pasteurized cream (30% fat) revealed delta-decalactone, (Z)-6-dodeceno-gamma-lactone, gamma-dodecalactone, delta-dodecalactone, and 3-methylindole with by far the highest flavor dilution (FD) factors among the 34 odor-active volatiles identified. Using a complementary approach involving silica column chromatography and fractionated high-vacuum distillation combined with sensory experiments enabled the additional identification of delta-tetradecalactone, delta-hexadecalactone, gamma-tetradecalactone, gamma-hexadecalactone, and delta-octadecalactone as semivolatile flavor components in the cream fat. Although a series of lactones is present in dairy cream, spiking of cream samples with individual lactones revealed that only the delta-tetradecalactone is able to enhance the typical retronasal creamy flavor of the product when added in amounts above its threshold level of 66 micromol/kg. Rather than contributing to the retronasal aroma of cream, first evidence was found that, particularly, gamma- and delta-octadecalactones and gamma- and delta-eicosalactones are able to influence the melting behavior of cream in the oral cavity.