University of Puerto Rico at Humacao

About: University of Puerto Rico at Humacao is a education organization based out in Humacao, Puerto Rico, United States. It is known for research contribution in the topics: Electrospinning & Nanofiber. The organization has 376 authors who have published 426 publications receiving 6485 citations. The organization is also known as: UPRH.

Variation in sexual reproduction in orchids and its evolutionary consequences: a spasmodic journey to diversification

Abstract: The great taxonomic diversity of the Orchidaceae is often attributed to adaptive radiation for specific pollinators driven by selection for outcrossing. However, when one looks beyond the product to the process, the evidence for selection is less than overwhelming. We explore this problem by discussing relevant aspects of orchid biology and asking which aspects of reproduction explain the intricate pollination mechanisms and diversification of this family. We reaffirm that orchids are primarily pollination limited, the severity of which is affected by resource constraints. Fruit set is higher in temperate than in tropical species, and in species which offer pollinator rewards than those that do not. Reproductive success is skewed towards few individuals in a population and effective population sizes are often small. Population structure, reproductive success and gene flow among populations suggest that in many situations genetic drift may be as important as selection in fostering genetic and morphological variation in this family. Although there is some evidence for a gradualist model of evolutionary change, we believe that the great diversity in this family is largely a consequence of sequential and rapid interplay between drift and natural selection. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84, 1–54.

The Genome Sequence of Psychrobacter arcticus 273-4, a Psychroactive Siberian Permafrost Bacterium, Reveals Mechanisms for Adaptation to Low-Temperature Growth

Abstract: Psychrobacter arcticus strain 273-4, which grows at temperatures as low as -10 degrees C, is the first cold-adapted bacterium from a terrestrial environment whose genome was sequenced. Analysis of the 2.65-Mb genome suggested that some of the strategies employed by P. arcticus 273-4 for survival under cold and stress conditions are changes in membrane composition, synthesis of cold shock proteins, and the use of acetate as an energy source. Comparative genome analysis indicated that in a significant portion of the P. arcticus proteome there is reduced use of the acidic amino acids and proline and arginine, which is consistent with increased protein flexibility at low temperatures. Differential amino acid usage occurred in all gene categories, but it was more common in gene categories essential for cell growth and reproduction, suggesting that P. arcticus evolved to grow at low temperatures. Amino acid adaptations and the gene content likely evolved in response to the long-term freezing temperatures (-10 degrees C to -12 degrees C) of the Kolyma (Siberia) permafrost soil from which this strain was isolated. Intracellular water likely does not freeze at these in situ temperatures, which allows P. arcticus to live at subzero temperatures.

Psychrobacter cryohalolentis sp. nov. and Psychrobacter arcticus sp. nov., isolated from Siberian permafrost.

Abstract: Three Gram-negative, non-motile, non-pigmented, oxidase-positive coccobacilli capable of growth at temperatures from −10 to 30 °C and salinities of 0 to 1.7 M NaCl were isolated from Siberian permafrost and characterized. Both 16S rRNA and gyrB gene sequencing studies placed the isolates in the Gammaproteobacteria within the genus Psychrobacter. However, with higher bootstrap values and reproducible tree topologies, gyrB represented a more reliable phylogenetic marker for the taxonomy of Psychrobacter species. DNA–DNA hybridization data supported gyrB tree topologies and established two relatedness groups within the three isolates; neither of these groups was related at the species level to any previously described Psychrobacter species. The two groups of isolates could be differentiated phenotypically from 13 previously described Psychrobacter species using API strips. These results support the existence of two novel species of Psychrobacter, for which we propose the names Psychrobacter cryohalolentis sp. nov. (type strain K5T=DSM 17306T=VKM B-2378T) and Psychrobacter arcticus sp. nov. (type strain 273-4T=DSM 17307T=VKM B-2377T).