Xylose anaerobic conversion by open-mixed cultures

Xylose is, after glucose, the dominant sugar in agricultural wastes. In anaerobic environments, carbohydrates are converted into volatile fatty acids and alcohols. These can be used as building blocks in biotechnological or chemical processes, e.g., to produce bioplastics. In this study, xylose fermentation by mixed microbial cultures was investigated and compared with glucose under the same conditions. The product spectrum obtained with both substrates was comparable. It was observed that, in the case of xylose, a higher fraction of the carbon was converted into catabolic products (butyrate, acetate, and ethanol) and the biomass yield was approximately 20% lower than on glucose, 0.16 versus 0.21 Cmol X/Cmol S. This lower yield is likely related to the need of an extra ATP during xylose uptake. When submitted to a pulse of glucose, the population cultivated on xylose could instantaneously convert the glucose. No substrate preference was observed when glucose and xylose were fed simultaneously to the continuously operated bioreactor.     

Prolactin-induced cytologic changes in the mucosa of the pigeon crop during crop-“milk” formation

Summary Light and electron microscope observations reveal two basic histo- and cytologic changes which take place in the pigeon crop during the course of prolaction administration to both sexes; (1) an increase in mitotic activity resulting in hyperplasia of the lateral lobes of the crop and (2) the accumulation of lipid in cells of these lobes. The latter process begins about twelve hours following prolactin injection. Histologic and cytochemical tests, as well as thin layer chromatographic analysis, reveal that these lipids may be classified as neutral unsaturated triglycerides. Tissues of control and prolactin-treated groups examined during the course of this study do not reveal any striking changes in organelle systems — aside from the accumulation of large lipid droplets. It does appear, however, that while ribosomes exist primarily as single units in non-stimulated cells, they appear primarily as polysomes in stimulated cells actively engaged in lipid synthesis. The origin of the cytoplasmic lipid inclusions is of interest. Morphologic evidence suggests that (1) they are not the result of cyto-pathologic changes, (2) they do not result from mitochondrial transformation and (3) they are not incorporated as discrete triglyceride micelles into these cells. The availability of precursors to the cell is dicussed in light of the observation that intercellular channels increase in width, and microvilli and desmosomes decrease in number throughout the experimental series. The incorporation of possible precursors into the cytoplasm may occur via two distinct classes of vesicles. One class is thought to arise through micropinocytotic activity. These vesicles have filamentous boundaries which are thought to render them specific for certain classes of compounds. The second class is somewhat larger in size and differs morphologically from micropinocytotic vesicles. These are thought to arise by the fusion of tips of microvilli and the plasma membrane, thus inpounding and internalizing materials from the intercellular canals into the cytoplasm.The author is indebted to Dr. Everett Anderson for his valuable criticism and encouragement offered during the course of this work. The investigation was supported in part by a Pre-Doctoral Fellowship (1-F1-GM-20, 296-01) from the National Institutes of Health and in part by grant GM-08776 from the National Institutes of Health awarded to Dr. Everett Anderson.     

Darwin's vexing contrivance: a new hypothesis for why some flowers have two kinds of anther

Heteranthery, the presence of two or more anther types in the same flower, is taxonomically widespread among bee-pollinated angiosperms, yet has puzzled botanists since Darwin. We test two competing hypotheses for its evolution: the long-standing ‘division of labour'' hypothesis, which posits that some anthers are specialized as food rewards for bees whereas others are specialized for surreptitious pollination, and our new hypothesis that heteranthery is a way to gradually release pollen that maximizes pollen delivery. We examine the evolution of heteranthery and associated traits across the genus Clarkia (Onagraceae) and study plant–pollinator interactions in two heterantherous Clarkia species. Across species, heteranthery is associated with bee pollination, delayed dehiscence and colour crypsis of one anther whorl, and movement of that anther whorl upon dehiscence. Our mechanistic studies in heterantherous species show that bees notice, forage on and export pollen from each anther whorl when it is dehiscing, and that heteranthery promotes pollen export. We find no support for division of labour, but multifarious evidence that heteranthery is a mechanism for gradual pollen presentation that probably evolved through indirect male–male competition for siring success.     

Foraging shifts and visual preadaptation in ecologically diverse bats

Changes in behaviour may initiate shifts to new adaptive zones, with physical adaptations for novel environments evolving later. While new mutations are commonly considered engines of adaptive change, sensory evolution enabling access to new resources might also arise from standing genetic diversity, and even gene loss. We examine the relative contribution of molecular adaptations, measured by positive and relaxed selection, acting on eye‐expressed genes associated with shifts to new adaptive zones in ecologically diverse bats from the superfamily Noctilionoidea. Collectively, noctilionoids display remarkable ecological breadth, from highly divergent echolocation to flight strategies linked to specialized insectivory, the parallel evolution of diverse plant‐based diets (e.g., nectar, pollen and fruit) from ancestral insectivory, and—unusually for echolocating bats—often have large, well‐developed eyes. We report contrasting levels of positive selection in genes associated with the development, maintenance and scope of visual function, tracing back to the origins of noctilionoids and Phyllostomidae (the bat family with most dietary diversity), instead of during shifts to novel diets. Generalized plant visiting was not associated with exceptional molecular adaptation, and exploration of these novel niches took place in an ancestral phyllostomid genetic background. In contrast, evidence for positive selection in vision genes was found at subsequent shifts to either nectarivory or frugivory. Thus, neotropical noctilionoids that use visual cues for identifying food and roosts, as well as for orientation, were effectively preadapted, with subsequent molecular adaptations in nectar‐feeding lineages and the subfamily Stenodermatinae of fig‐eating bats fine‐tuning pre‐existing visual adaptations for specialized purposes.     

The biology and ecology of coral rubble and implications for the future of coral reefs

Coral Reefs - Structural complexity provided by the living coral reef framework is the basis of the rich and dynamic biodiversity in coral reefs. In many cases today, the reduction in habitat...